Grids Reference Page

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Revision as of 12:10, 2 August 2011 by BigChimp (talk | contribs) (When above customizaton is not enough, derived grids: typos)

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Contents

Objective

This text will try to show the user some aspects of the grids components in Lazarus. Also is intended to serve as a guide for users who never used grids before (as experienced users generally only need a reference for new functionality). So this text will try to reach the following objectives:

  1. To introduce the grids components to people with little or not previous Delphi contact.
  2. To document the differences with respect to Delphi grids components.
  3. To document the new functionality in Lazarus grids.
  4. Create reference and examples for the components.

Overview

A grid is a component that provides a mean for display data in tabular format. The most obvious characteristic of grids is that they are composed of cells forming rows and columns.

The type of information that can be shown in a grid is very ample and mainly depends on what the user wants to show. Generally this information consists of text, colors, images or a combination of those three.

Given the great variety of information that can be represented, a series of grids exits whose purpose is to facilitate the user in showing specific kinds of information.

Inheritance Tree

                      [TCustomControl]           
                              |                    
                              |                    
                         TCustomGrid               
                              |                    
                +-------------+------------+       
                |                          |       
          TCustomDrawGrid             TCustomDbGrid
                |                          |       
       +--------+--------+                 |       
       |                 |              TDbGrid    
   TDrawGrid      TCustomStringGrid                
                         |                         
                         |                         
                    TStringGrid                    

A Starting Example

As one of the objectives of this page is to help people with little or no previous Lazarus knowledge let's do a quick starting example of grids in action. Why not, let's make a traditional "hello world" example using the TStringGrid Component.

  1. Create a new application.
    • From the main menu select: project->New Project
    • In the Create New Project dialog press the "Create Button"
    • A new empty form will be shown.
  2. Place a grid on the form
    • From the component palette select the "additional" tab
    • Click over the TStringGrid icon []
    • Click over the form, near to the top left corner. A new empty grid appears.
  3. Place a button on the form
    • From the component palette select the "Standard" tab
    • Click over the TButton icon []
    • Click over a empty area of the form. A new button appears.
  4. Doubleclick the button from the step 3, and write down the following code in the click button handler:
    • Stringgrid1.Cells[1,1] := 'Hi World!';
  5. Run the program by clicking the play icon []
    • by pressing the button1, the hello world text should appear in cell column 1, row 1.

Differences between Lazarus and Delphi grids

The current grids components present several differences with respect to Delphi grids. This is mainly because the Lazarus grids were created from scratch primarily without trying to make them fully compatible.

At a later stage, compatibility with Delphi's grids became a desired objective and the grids started to conform more closely to the Delphi grid's interface, but even then this was done without a strong effort to make every single property or method match its Delphi counterpart. Also, because the grid's internals are very different, some things are not possible or need to be done in a different way in the Lazarus' grids. As the grids have evolved, greater compatibility has been achieved and this is desirable.

Differences

Here the known differences will be listed, in no special order.

  • Cell Editors
  • Designtime Behaviour
  • Cell Drawing has some differences, see customizing grid section.

New Functionality

  • Columns
  • Events
  • Grid Editor

Adjustments for improving Delphi grids compatibility

Here is a list of properties and adjustments that can be made in order to make Lazarus grids look or behave similar to Delphi grids. These adjustments are based in a newly created grid. Entries tagged with [Code] need to be set in code, [Design] entries can be changed at design time.

  • [Design] TitleStyle := tsStandard;
  • [Design] DefaultRowHeight := 24;
  • [Code] EditorBorderStyle := bsNone; // this might work only on windows.
  • [Code] UseXORFeatures := true;
  • [Code] AllowOutBoundEvents := False; {r10992 or later}
  • [Code] FastEditing := False; (supported in dbgrid. StringGrid req. r10992 or later)
  • [Design] AutoAdvance := aaNone;

Grids Reference

Information

The starting point for reference about TCustomGrid, TDrawGrid, TCustomDrawGrid, TCustomStringGrid and TStringGrid is the unit Grids.pas reference

For TCustomDBGrid and TDBgrid it is the unit DBGrids.pas reference

Until recently there has not been much content in these links, due partly to the lack of a tool that allows easily maintenance of its content: but such tool has been constructed and the gaps are being filled.

In general, any Delphi reference about the grids should help us to use Lazarus grids (but don't forget that there are several differences between Delphi and Lazarus grids that we have documented); with this in mind and as a temporary place for reference information, this place will be used to document things that don't work the same as in Delphi, as well as any new functionality.

TODO: the rest of this section will disappear; its content will be moved to unit Grids.pas reference

TCustomGrid

See the full TCustomGrid Reference

property OnBeforeSelection: TOnSelectEvent

property OnCompareCells: TOnCompareCells

property OnPrepareCanvas: TOnPrepareCanvasEvent

property OnDrawCell: TOnDrawCell

property OnEditButtonClick: TNotifyEvent

property OnSelection: TOnSelectEvent

property OnSelectEditor: TSelectEditorEvent

property OnTopLeftChanged: TNotifyEvent

procedure AutoAdjustColumns;

procedure BeginUpdate;

procedure Clear;

procedure DeleteColRow(IsColumn: Boolean; index: Integer);

function EditorByStyle(Style: TColumnButtonStyle): TWinControl;

procedure EndUpdate(UO: TUpdateOption); overload;

procedure EndUpdate(FullUpdate: Boolean); overload;

procedure EndUpdate; overload;

procedure ExchangeColRow(IsColumn: Boolean; index, WithIndex:Integer);

function IscellSelected(aCol,aRow: Integer): Boolean;

function IscellVisible(aCol, aRow: Integer): Boolean;

procedure LoadFromFile(FileName: string);

function MouseToCell(Mouse: TPoint): TPoint; overload;

function MouseToLogcell(Mouse: TPoint): TPoint;

function MouseToGridZone(X,Y: Integer): TGridZone;

function CellToGridZone(aCol,aRow: Integer): TGridZone;

procedure MoveColRow(IsColumn: Boolean; FromIndex, ToIndex: Integer);

procedure SaveToFile(FileName: string);

procedure SortColRow(IsColumn: Boolean; index:Integer); overload;

procedure SortColRow(IsColumn: Boolean; index,FromIndex,ToIndex: Integer); overload;

property AllowOutboundEvents:boolean;

protected in TCustomGrid, public in TCustomDrawGrid and descendants. Normally when user do click on a point over empty space after cells (for example if grid has three rows but user clicks on imaginary fourth row) the current focused cell will move to the nearest cell to clicked point, we call this an outbound event, default value is true as this has been grid's behaviour since begining. This property was added to simulate Delphi behaviour where outbound events are not available, to enable delphi compatibility set this property to false.

TCustomStringGrid

TCustomStringGrid serves as the base for TStringGrid. It can be used for derived TStringGrid components that want to hide published properties. See new intermediate grids for more information.

The following properties or methods are public and are also available to TStringGrid.

See the full TCustomStringGrid Reference

procedure AutoSizeColumn(aCol: Integer);

This procedure sets the column width to the size of the widest text it finds in all rows for the column aCol. Tip: see the goDblClickAutoSize option to allow columns to be automatically resized when doubleClicking the column border.

procedure AutoSizeColumns;

Automatically resizes all columns by adjusting them to fit in the longest text in each column. This is a quick method of applying AutoSizeColumn() for every column in the grid.

procedure Clean; overload;

Cleans all cells in the grid, fixed or not.

procedure Clean(CleanOptions: TGridZoneSet); overload;

Cleans all cells in the grid subject to the given CleanOptions. See TGridZoneSet for more information. Some examples:

  • Clean all cells: grid.Clean([]); (the same as grid.clean)
  • Clean all non fixed cells: grid.Clean([gzNormal]);
  • Clean all cells but don't touch grid column headers: Grid.Clean([gzNormal, gzFixedRows]);

procedure Clean(StartCol,StartRow,EndCol,EndRow: integer; CleanOptions:TGridZoneSet); overload;

does the same as Clean(CleanOptions:TGridZoneSet) but restricted to the given StartCol,StartRow,EndCol and EndRow. Examples:

  • Clean column index 4 to 6 but don't touch grid column headers: many variations, Grid.Clean(4,Grid.FixedRows,6,Grid.RowCount-1,[]); Grid.Clean(4,0,6,Grid,RowCount-1, [gzNormal]); etc.

procedure Clean(aRect: TRect; CleanOptions: TGridZoneSet); overload;

The same as Clean(StartCol,StartRow,EndCol,EndRow, CleanOptions), just taking a TRect instead of individual cell coordinates. Useful to clean the selection: grid.Clean(Grid.Selection,[]);

property Cols[index: Integer]: TStrings read GetCols write SetCols;

Get/set a list of strings from/to the given grid's column index starting from row index 0 to RowCount-1.

Examples
  • Set Example: Set the content of the third column in the grid from a ListBox:

<delphi>Grid.Cols[2] := ListBox1.Items;</delphi>

  • Get Example: Set the content of a Listbox from the grid's column index 4:

<delphi>procedure TForm1.FillListBox1; var

 StrTempList: TStringList;

begin

 StrTempList := TStringList(Grid.Cols[4]);
 if StrTempList<>nil then begin
   ListBox1.Items.Assign(StrTempList);
   StrTempList.Free;
 end;

end;</delphi>

Notes.

This property works differently in Lazarus and in Delphi when getting the data from the grid. In Lazarus a temporary TStringList object is created for retrieving the column content. It is the responsibility of the user to free this object after use.

This means also that changes in the returned list will not affect the grids content or layout.

See the Get Example.

property Rows[index: Integer]: TStrings read GetRows write SetRows;

Get/set a list of strings from/to the given grid's row index starting from column index 0 to column ColCount-1.

Notes.

This property works differently in Lazarus and in Delphi when getting the data from the grid. In Lazarus a temporary TStringList object is created for retrieving the row content. It is the responsibility of the user to free this object after use.

This means also that changes in the returned list will not affect the grid's content or layout.

Examples
  • Set Example: Set the content of the third row in the grid from a ListBox:

<delphi>Grid.Rows[2] := ListBox1.Items;</delphi>

  • Get Example: Set the content of a Listbox from the grid's row index 4:

<delphi>procedure TForm1.FillListBox1; var

 StrTempList: TStringList;

begin

 StrTempList := TStringList(Grid.Rows[4]);
 if StrTempList<>nil then begin
   ListBox1.Items.Assign(StrTempList);
   StrTempList.Free;
 end;

end;</delphi>

  • An Example that doesn't work, and its Fix: Retrieved string list is read only

<delphi>// this will not work and will cause memory leak // because returned StringList is not being freed Grid.Rows[1].CommaText := '1,2,3,4,5'; Grid.Rows[2].Text := 'a'+#13#10+'s'+#13#10+'d'+#13#10+'f'+#13#10+'g';

// fixing the first case Lst:=TStringList.Create; Lst.CommaText := '1,2,3,4,5'; Grid.Rows[1] := Lst; Lst.Free;</delphi>

property UseXORFeatures;

Boolean property, default value: False;

This property controls how the dotted focus rectangle appears in the grid. When True, the rectangle is painted using the XOR raster operation. This allow us to see the focus rectangle no matter what the cells' background color is. When False, the user can control the color of the dotted focus rectangle using the FocusColor property

It also controls the look of the column/row resizing. When True, a line shows visually the size that the the column or row will have if the user ends the operation. When False, the column or row resizing takes effect just as the user drags the mouse.

Grids Howto

Customizing grids

Grid are components derived from the TCustomControl class, and don't have a native widget associated with them which means that grids are not restricted by the look of current interface theme. This can be both an advantage and a disadvantage: usually programmers want to create a uniform-look application. The good news is that Lazarus grids are flexible enough to get something from both worlds; programmers can easily make grids look similar to other native controls, or they can customize the grid to the finest detail so they can obtain almost the same look in any platform or widget interface (that is, with the exception of scrollbars, because their look is still determined by the current theme).

Properties and Events for customizing grids

Some properties can affect the way the grid looks by acting when the cell is about to be painted in PrepareCanvas/OnPrepareCanvas by changing default canvas properties like brush color or font. Following is a list of such properties:

  • AlternateColor. With this the user can change the background color appears on alternated rows. This is to allow easy reading off of grid rows data.
  • Color. This sets the primary color used to draw non fixed cells background.
  • FixedColor. This is the color used to draw fixed cells background.
  • Flat. this eliminates the 3d look of fixed cells.
  • TitleFont. Font used to draw the text in fixed cells.
  • TitleStyle. This property changes the 3D look of fixed cells, there are 3 settings:
    • tsLazarus. This is the default look
    • tsNative. This tries to set a look that is in concordance with current widgetset theme.
    • tsStandard. This style is a more contrasted look, like delphi grids.
  • AltColorStartNormal. boolean, if true alternate color is always in the second row after fixed rows, the first row after fixed rows will be always color, if false default color is set to the first row as if there were no fixed rows.
  • BorderColor. This sets the grid's border color used when Flat:=True and BorderStyle:=bsSingle;
  • EditorBorderStyle. If set to bsNone under windows the cell editors will not have the border, like in delphi, set to bsSingle by default because the border can be theme specific in some widgetsets and to allow a uniform look.
  • FocusColor. The color used to draw the current focused cell if UseXORFeatures is not set, by default this is clRed.
  • FocusRectVisible. turns on/off the drawing of focused cell.
  • GridLineColor. color of grid lines in non fixed area.
  • GridLineStyle. Pen style used to draw lines in non fixed area, possible choices are: psSolid, psDash, psDot, psDashDot, psDashDotDot, psinsideFrame, psPattern,psClear. default is psSolid.
  • SelectedColor. Color used to draw cell background on selected cells.
  • UseXORFeatures. If set, focus rect is drawn using XOR mode so it should make visible the focus rect in combination with any cell color ackground. It also affects the moving columns look.
  • DefaultDrawing. boolean. Normally the grids prepare the grid canvas using some properties according to the kind of cell is being painted. If user write an OnDrawCell event handler, DefaultDrawing if set also paints the cell background, if user is drawing fully the cell is better turn off this property so painting is not duplicated. In a StringGrid if DefaultDrawing is set it draws the text in each cell.
  • AutoAdvance. where the cell cursor will go when pressing enter or tab/shift tab, or after editing.
  • ExtendedColSizing. If true user can resize columns not just at the headers but along the columns height.

Other properties that also affect the grids look.

Options. Options property is a set with some elements to enable diverse functionality but some are related directly with grid's look. This options can be set at designtime or runtime.

  • goFixedVertLine, goFixedHorzLine it draws a vertical or horizontal line respectively delimiting cells or columns in fixed area, active by default.
  • goVertLine, goHorzLine the same as previous, but for normal browseable area. A grid can be made to simulate a listbox by unsetting both of this elements.
  • goDrawFocusSelected if this element is enabled a selection background is painted in focused cell in addition to focused dotted rectangle (note this doesn't work yet when goRowSelect option is set, in such case row is always painted as if goDrawFocusSelected is set)
  • goRowSelect select the full row instead of individual cells
  • goFixedRowNumbering if set, grid will do numbering of rows in first fixed column
  • goHeaderHotTracking if set, the grid will try to show a different look when the mouse cursor is overing any fixed cell. In order for this to work, desired cell zone needs to be enabled with property HeaderHotZones. Try combining this option with property TitleStyle:=tsNative to get themed hot tracking look.
  • goHeaderPushedLook if set, this element enables a pushed look when clicking any fixed cell. The zone of "pushable" cells is enabled using HeaderPusedZones property.

(write more)

Description of grid's drawing process

Like other custom controls, the grid is drawn using the paint method. In general terms the grid is drawn by painting all rows, and each row by painting its individual cells.

The process is as follow:

  • First the visible cells area is determined: each row is tested to see if it intersects the canvas clipping region; if it's ok, then the visible area is painted by drawing columns of each row.
  • The column and row values are used to identify the cell that is about to be painted and again each column is tested for intersection with the clippling region; if everything is ok, some additional properties like the cell's rectangular extent and visual state are passed as arguments to the DrawCell method.
  • As the drawing process is running, the visual state of each cell is adjusted according to grid options and position within grid. The visual state is retained in a varible of type TGridDrawState which is a set with following elements:
    • gdSelected The cell will have a selected look.
    • gdFocused The cell will have a focused look.
    • gdFixed Cell have to be painted with fixed cell look.
    • gdHot the mouse is over this cell, so paint it with hot tracking look
    • gdPushed the cell is being clicked, paint it with pushed look
  • DrawCell. The DrawCell method is virtual and may be overriden in descendant grids to do custom drawing. The information passed to DrawCell helps to identify the particular cell is being painted, the physical area ocuppied in screen and its visible status. See DrawCell reference for details. For each cell the following occurs:
  • PrepareCanvas. In this method, if the DefaultDrawing property is set, the grid canvas is setup with default properties for brush and font based on current visual state. For several design and runtime properties, the text alignment is set to match programmer selection in custom columns if they exists. If DefaultDrawing is false, brush color is set to clWindow and Font color to clWindowText, the text alignment is set with grids defaultTextStyle property value.
  • OnPrepareCanvas. If the programmer wrote an event handler for OnPrepareCanvas event, it is called at this point. This event can be used for doing simple customization like changing cell's background color, font's properties like color, fontface and style, Text layout like different combinations of left, center, top, bottom, right alignment, etc. Any change made to the canvas in this event would be lost, because the next cell drawing will reset canvas again to a default state. So it's safe doing changes only for particular cell or cells and forget about it for the rest. Using this event sometimes helps to avoid using the OnDrawCell grid event, where users would be forced to duplicate the grid's drawing code. Todo: samples of what can be made and what to leave for OnDrawCell?...
  • OnDrawCell. Next if no handler for OnDrawCell event was specified, the grid calls the DefaultDrawCell method which simply paints the cell background using the current canvas brush color and style. If the OnDrawCell handler exists, the grid first paints the cell background but only if DefaultDrawing property was set, then it calls OnDrawCell event to do custom cell painting. Usually programmers want to do custom drawing only for particular cells, but standard drawing for others; in this case, they can restrict custom operation to certain cell or cells by looking into ACol, ARow and AState arguments, and for other cells simply call DefaultDrawCell method and let the grid to take care of it.
  • Text. At this point (only for TStringGrid) if DefaultDrawing property is true, the cell's text content is painted.
  • Grid lines. The last step for each cell is to paint the grid lines: if grid options goVertLine, goHorzLine, goFixedVertLine and goFixedHorzLine are specified the cell grid is drawn at this point. Grids with only rows or only cols can be obtained by changing these options. If the programmer elected to have a "themed" look it is done at this point also (see property TitleStyle).
  • FocusRect. When all columns of current row have been painted it is time to draw the focus rectangle for the current selected cell or for the whole row if goRowSelect option is set.

Grid's cell selection

The location of a grid's current (focused) cell (or row) can be changed using keyboard, mouse or through code. In order to change cell focus successfully to another position, we must test the target position to see if it is allowed to receive cell focus. When using keyboard, the property AutoAdvance performs part of the process by finding what should be the next focused cell. When using mouse clicks or moving by code, focus will not move from the current cell unless the target cell is permitted to receive focus.

The grid calls function SelectCell to see if a cell is focusable: if this function returns true, then the target cell identified with arguments aCol and aRow is focusable (the current implementation of TCustomGrid simply returns true). TCustomDrawGrid and hence TDrawGrid and TStringGrid override this method to check first if cell is any wider than 0; normally you don't want a 0 width cell selected so a cell with this characteristics is skipped automatically in the process of finding a suitable cell. The other thing the overriden method SelectCell does is to call the user configurable event OnSelectCell: this event receives the cell coordinates as arguments and always returns a default result value of true.

Once a cell is known to be focusable and we are sure a movement will take place, first the method BeforeMoveSelection is called; this in turns triggers the OnBeforeSelection event. This method's arguments are the coordinates for the new focused cell, at this point any visible editor is hidden too. The "before" word means that selection is not yet changed and current focused coordinates can be accessed with grid.Col and grid.Row properties.

After that, the internal focused cell coordinates are changed and then method MoveSelection is called; this method's purpose is to trigger the OnSelection event if set (this is a notification that the focused cell has, by this time, already changed and cell coordinates are now available through grid.row and grid.col properties).

Note that is not good to use OnSelectCell event to detect cell focus changes, as this event will be triggered several times even for the same cell in the process of finding a suitable cell. Is better to use OnBeforeSelection or OnSelection events for this purpose.

Several differences with Delphi have been identified

  • In Lazarus TCustomGrid.DrawCell method is not abstract and its default implementation does basic cell background filling.
  • In Delphi, the cell's text is drawn before entering the OnDrawCell event (see bug report #9619).
  • SelectCell and OnSelectCell behaviour is probably different - can't really comment on the differences. In Lazarus they are used in functionality like AutoAdvance which as far as I know doesn't exist in Delphi.

When above customizaton is not enough: derived grids

Derived grids usually have to override the following methods:
DrawAllRows: Draws all visible rows.
DrawRow: Draws all cells in a row.
DrawRow draws all cells in the row by first checking if cell is within clipping region, and only draws the cell if it is.
DrawCell:
DrawCellGrid:
DrawCellText:
DrawFocusRect:
(write me).

Operations

Focusing a cell

Focusing a cell in TStringGrid is easy. Note that counting starts from zero not 1. So to focus row 10, column 9, do:

<delphi>StringGrid1.row := 9; StringGrid1.col := 8;</delphi>

Save and Retrieve Grid Content

The SaveToFile procedure allows you save the TStringGrid format, attributes & values to a XML file. Previously you must set the SaveOptios property as follow:

soDesign:     Save & Load ColCount,RowCount,FixedCols,FixedRows,
              ColWidths, RowHeights and Options (TCustomGrid)
soPosition:   Save & Load Scroll Position, Row, Col and Selection (TCustomGrid)
soAttributes: Save & Load Colors, Text Alignment & Layout, etc. (TCustomDrawGrid)
soContent:    Save & Load Text (TCustomStringGrid)

The LoadFromFile procedure allows you to load into a StringGrid instance, attributes, formats & values, from a XML file. First, you must set some of this options of the SaveOptions property (on your TStringGrid instance) SaveOptions

 soDesign:     Save & Load ColCount,RowCount,FixedCols,FixedRows,
               ColWidths, RowHeights and Options (TCustomGrid)
 soPosition:   Save & Load Scroll Position, Row, Col and Selection (TCustomGrid)
 soAttributes: Save & Load Colors, Text Alignment & Layout, etc. (TCustomDrawGrid)
 soContent:    Save & Load Text (TCustomStringGrid)

Example:

  1. First, go to menu "File -> New -> Application";
  2. Put an empty TStringGrid;
  3. Put a TButton and TOpenDialog;
  4. Add the event OnCreate for the Form;
  5. Add the event OnClick for the Button.

<delphi>unit Unit1;

{$mode objfpc}{$H+}

interface

uses

 Classes, SysUtils, LResources, Forms, Controls, Graphics, Dialogs, Grids,
 Buttons, StdCtrls, XMLCfg;

type

 { TForm1 }
 TForm1 = class(TForm)
   StringGrid1: TStringGrid;
   Button1: TButton;
   OpenDialog1: TOpenDialog;
   procedure Button1Click(Sender: TObject);
   procedure Form1Create(Sender: TObject);
 private
   { private declarations }
 public
   { public declarations }
 end; 

var

 Form1: TForm1; 

implementation

{ TForm1 }

procedure TForm1.Form1Create(Sender: TObject); begin

//sets the SaveOptions at creation time of the form 
stringgrid1.SaveOptions := [soDesign,soPosition,soAttributes,soContent];

end;


procedure TForm1.Button1Click(Sender: TObject); begin

//Ask if thew Execute method of the OpenDialog was launched 
//when this occurs, the user selects an XML file to Load
//wich name was stored in the FileName prop.
if opendialog1.Execute then
Begin
  //Clear the grid 
  StringGrid1.Clear;
  //Load the XML
  StringGrid1.LoadFromFile(OpenDialog1.FileName);
  //Refresh the Grid
  StringGrid1.Refresh;
End;

end;

initialization

 {$I unit1.lrs}

end.</delphi>


The sample xml file: (Copy the text below into a txt file. Don't forget put the xml header :-)) <xml><?xml version="1.0"?> <CONFIG>

 <grid version="3">
   <saveoptions create="True" position="True" content="True"/>
   <design columncount="2" rowcount="5" fixedcols="1" fixedrows="1" defaultcolwidth="64" defaultRowHeight="20">
     <options>
       <goFixedVertLine value="True"/>
       <goFixedHorzLine value="True"/>
       <goVertLine value="True"/>
       <goHorzLine value="True"/>
       <goRangeSelect value="True"/>
       <goDrawFocusSelected value="False"/>
       <goRowSizing value="False"/>
       <goColSizing value="False"/>
       <goRowMoving value="False"/>
       <goColMoving value="False"/>
       <goEditing value="False"/>
       <goTabs value="False"/>
       <goRowSelect value="False"/>
       <goAlwaysShowEditor value="False"/>
       <goThumbTracking value="False"/>
       <goColSpanning value="False"/>
       <goRelaxedRowSelect value="False"/>
       <goDblClickAutoSize value="False"/>
       <goSmoothScroll value="True"/>
     </options>
   </design>
   <position topleftcol="1" topleftrow="1" col="1" row="1">
     <selection left="1" top="1" right="1" bottom="1"/>
   </position>
   <content>
     <cells cellcount="10">
       <cell1 column="0" row="0" text="Title Col1"/>
       <cell2 column="0" row="1" text="value(1.1)"/>
       <cell3 column="0" row="2" text="value(2.1)"/>
       <cell4 column="0" row="3" text="value(3.1)"/>
       <cell5 column="0" row="4" text="value(4.1)"/>
       <cell6 column="1" row="0" text="Title Col2"/>
       <cell7 column="1" row="1" text="value(1.2)"/>
       <cell8 column="1" row="2" text="value(2.2)"/>
       <cell9 column="1" row="3" text="value(3.2)"/>
       <cell10 column="1" row="4" text="value(4.2)"/>
     </cells>
   </content>
 </grid>

</CONFIG></xml>


--Raditz 21:06, 11 Jan 2006 (CET) from ARGENTINA

Grid Cell Editors

The grid uses cell editors to change the content of cells.

For a specialized grid like TStringGrid, the editor is the usual single line text editor control, but sometimes it's desirable to have other means to enter information. For example, to call the open file dialog to find the location of a file so the user doesn't have to type the full path manually; if the text in the cell represents a date, it would be more friendly if we could popup a calendar so we can choose a specific date easily.

Sometimes the information the user should enter in a cell is restricted to a limited list of words; in this case typing the information directly might introduce errors and validating routines might need to be implemented. We can avoid this by using a cell editor that presents the user with a list containing only the legal values.

This is also the case for generic grids like TDrawGrid where the user needs some kind of structure to hold the data that will be shown in the grid. In this situation, the information that is entered in the cell editor updates the internal structure to reflect the changes in the grid.

Builtin cell editors

The grids.pas unit already includes some of the most used cell editors ready for use in grids. It is also possible to create new cell editors (custom cell editors) if the built-in editors are not appropiate for a specific task.

The builtin cell editors are Button, Edit, and Picklist.

Using cell editors

Users can specify what editor will be used for a cell using one of two methods.

  1. Using a custom column and selecting the ButtonStyle property of the column. In this method the user can select the style of the editor that will be shown. Available values are: cbsAuto, cbsEllipsis, cbsNone, cbsPickList, cbsCheckboxColumn, cbsButtonColumn.
  2. Using OnSelectEditor grid event. Here the user specifies in the Editor parameter which editor to use for a cell identified for column aCol and row ARow in a TCustomDrawGrid derived grid or TColumn in TCustomDBGrid. For this purpose there is a useful public function of grids, EditorByStyle() that takes as parameter one of the following values: cbsAuto, cbsEllipsis, cbsNone, cbsPickList, cbsCheckboxColumn, cbsButtonColumn. This method takes precedence over the first one using custom columns. A Custom cell editor can be specified here. This event is also the place to setup the editor with values specific to the cell, row or column.

Description of editor styles

The following is a description of the editor styles. They are enumerated values of type TColumnButtonStyle and so they are prefixed by 'cbs'. This type was used to remain compatible with Delphi's DBGrid.

  • cbsAuto
This is the default editor style for TCustomGrid derived grids. The actual editor class that will be used to edit the cell content depends on several factors. For TCustomGrids it uses a TStringCellEditor class derived from TCustomMaskEdit. This editor is specialized to edit single line strings. It is then used in TStringGrid and TDrawGrid by default. When using Custom Columns, if the programmer filled the Column's PickList property, this behaves as if cbsPickList editor style was set. For a TCustomDBGrid that has a field of type boolean, it behaves as if cbsCheckBoxColumn editor style was specified. This is the recommended value for Custom Cell Editors. TODO: related OnEditingDone.
  • cbsEllipsis
This editor style is the most generic one. When used, a button appears in the editing cell and programmers could use the OnEditButtonClick grid event to detect when the user has pressed the button and take any action programmed for such a cell. For example a programmer could use this editor style to pop up a calendar dialog to allow the user easily to select a specific date. Other possibilities could be to show a file open dialog to find files, a calculator so user can enter the numeric result of calcs, etc.
OnEditButtonClick is just a notification, to find out in which cell a button has been clicked by taking a look at the grid.Row and grid.Col properties.
A DBGrid has specific properties to retrieve the active column or field and because this event occurs in the active record, it could update the information in the active field.
This editor style is implemented using TButtonCellEditor, a direct descendant of TButton.
  • cbsNone
This editor style instructs the grid not to use any editor for a specific cell or column; it behaves then, as if the grid were readonly for such a cell or column.
  • cbsPickList
Used to present the user with a list of values that can be entered. This editor style is implemented using TPickListCellEditor, a component derived from TCustomComboBox. The list of values that are shown is filled in one of two ways depending on the method used to select the editor style.
  1. When using custom columns, programmers can enter a list of values using the column's PickList property. [FOR BEGINNERS: TODO: exact procedure to edit the list]
  2. In OnSelectEditor, programmers get the TPickListCellEditor instance using the function EditorByStyle(cbsPickList). See here for an example
The value in a TStringGrid grid will automatically reflect the value selected. If necessary the programmer could detect the moment the value is selected by writing an event handler for the grid's OnPickListSelect event, so additional steps can be taken (for example, to process the new value). TODO: related OnEditingDone.
  • cbsCheckboxColumn
It can be useful when the data content associated with the column is restricted to a pair of values, for example, yes-no, true-false, on-off, 1-0, etc. Instead of forcing the user to type the values for this kind of data in a StringCellEditor or to choose one from a list, cbsCheckboxColumn is used to modify the data of a column by using a checkbox representation that the user can toggle by using a mouse click or pressing the SPACE key.
If a columns' ButtonStyle property is set to cbsAuto and DBGrid detects that the field associated with the column is a boolean field, then the grid uses this editor style automatically. This automatic selection can be disabled or enabled using DBGrid's OptionsExtra property; setting dgeCheckboxColumn element to false disables this feature.
The values that are used to recognize the checked or unchecked states are set in a column's properties ValueChecked and ValueUnchecked.
At any moment, the field value can be in one to three states: Unchecked, Checked or Grayed. Internally these states are identified by the following values of type TDBGridCheckBoxState: gcbpUnChecked, gcbpChecked and gcbpGrayed.
This editor style doesn't use real TCheckbox components to handle user interaction: the visual representation is given by three built-in bitmap images that corresponds to the possible states of checkbox. The used bitmaps can be customized by writing a handler for DBGrid event OnUserCheckboxBitmap; the handler of this event gets the state of the checkbox in the parameter CheckedState of type TDBGridCheckboxState and a bitmap parameter that the programmer could use to specify custom bitmaps.
  • cbsButtonColumn
This editor style is used to show a button on every cell on column. Like in the case of cbsCheckboxColumn this editor do not use real buttons, the appearance is defined by current widgetset theme.
The user knows what particular button was pressed by handling the grid's OnEditButtonClick and checking grid's col and row. Note that in this particular case, grid's col and row do not identify the currently selected cell, but the cell of the clicked button. Once the OnEditButtonClick event has been handled, and if the user has not modified the grid's col or row in this handler, the grid automatically resets the col and row to reflect the currently selected cell. While handling the OnEditButtonClick the current grid selection is available in grid.Selection which is a TRect property, left and right represent Column indexes, Top and Bottom are row indexes.
The button's caption is the corresponding cell string.

Example: How to set a custom cell editor

See lazarus/examples/gridcelleditor/gridcelleditor.lpi

Example: How to add a button editor

<delphi>// Conditionally show button editor in column index 1 or 2 if // cell in column index 1 is empty procedure TForm1.StringGrid1SelectEditor(Sender: TObject; aCol, aRow: Integer;

 var Editor: TWinControl);

begin

 if (aCol = 1) or (aCol = 2) then
   if StringGrid1.Cells[1,aRow] =  then
   begin
     Editor := StringGrid1.EditorByStyle(cbsEllipsis);
   end;
 end;

// Triggering Action ... procedure TForm1.StringGrid1EditButtonClick(Sender: TObject); begin

 if StringGrid1.Col = 1 then Showmessage('column 1 editor clicked');
 if StringGrid1.Col = 2 then Showmessage('column 2 editor clicked');

end;</delphi>

Example: Working with Picklist, How to make it read only and How to fill it at run time.

Using grid's event OnSelectEditor one can customize how PickList editor (see cbsPickList button style) behaves. In next example the picklist editor from column 1 is modified so on odd rows the user can enter values by typing, on even rows the values are limited to the ones contained in its list. Also, this example show how to fill the list with different values depending on the row being processed. <delphi> procedure TForm1.gridSelectEditor(Sender: TObject; aCol, aRow: Integer;

 var Editor: TWinControl);

begin

 if aCol=1 then begin
   if (Editor is TCustomComboBox) then
     with Editor as TCustomComboBox do begin
       if (aRow mod 2=0) then
         Style := csDropDown
       else
         Style := csDropDownList;
       case aRow of
         1:
           Items.CommaText := 'ONE,TWO,THREE,FOUR';
         2:
           Items.CommaText := 'A,B,C,D,E';
         3:
           Items.CommaText := 'MX,ES,NL,UK';
         4:
           Items.CommaText := 'RED,GREEN,BLUE,YELLOW';
       end;
     end;
 end;

end; </delphi>

Aligning text in StringGrids

This code shows how to use different text alignments in columns 2 and 3. <delphi>procedure TForm1.StringGrid1PrepareCanvas(sender: TObject; aCol, aRow: Integer;

 aState: TGridDrawState);

var

 MyTextStyle: TTextStyle;

begin

 if (aCol=2) or (aCol=3) then
 begin
   MyTextStyle := StringGrid1.Canvas.TextStyle;
   if aCol=2 then
     MyTextStyle.Alignment := taRightJustify 
   else 
   if aCol=3 then
     MyTextStyle.Alignment := taCenter;
   StringGrid1.Canvas.TextStyle := MyTextStyle;
 end;

end;</delphi>

Multilines in Grids

This sample shows how to make multilined text in cells[3,2], it works the same for DBGrid where OnPrepareCanvas have parameters for dealing with TColumns and from there with TFields. <delphi>procedure TForm1.StringGrid1PrepareCanvas(sender: TObject; aCol, aRow: Integer;

 aState: TGridDrawState);

var

 MyTextStyle: TTextStyle;

begin

 if (aRow=2) or (aCol=3) then
 begin
   MyTextStyle := StringGrid1.Canvas.TextStyle;
   MyTextStyle.SingleLine := false;
   StringGrid1.Canvas.TextStyle := MyTextStyle;
 end;

end;</delphi>

Validating Entered Values

Lazarus version 0.9.29 introduces StringGrid OnValidateEntry event of type TValidateEntryEvent which has following declaration:

<Delphi>TValidateEntryEvent =

 procedure(sender: TObject; aCol, aRow: Integer;
           const OldValue: string; var NewValue: string) of object;</Delphi>
aCol,aRow are the cell coordinates of cell being validated.
OldValue is the value that was in cells[aCol,aRow] before editing started.
NewValue is the value that will be finally inserted in cells[aCol,aRow].

Because of the way StringGrid works by setting the cell value while user is editing (see grid's OnSetEditText event and SetEditText method) when the OnValidateEntry event triggers, the cell already contains the entered value being valid or not, using event arguments OldValue and NewValue the cell value can be validated and changed accordingly.

Usually validation occurs when user has moved to another cell, if validation fails is desireable to keep the cell editor visible so the entered value can be corrected by user. To let the grid know that validation has failed an exception needs to be raised, the grid will handle the exception to Application.HandleException and any movement is cancelled. For example, suppose that cell[1,1] should hold only values 'A' or 'B' validation could be made with:

<Delphi>procedure TForm1.GridValidateEntry(sender: TObject; aCol,

 aRow: Integer; const OldValue: string; var NewValue: String);

begin

 if (aCol=1) and (aRow=1) then begin
   if grid.Cells[aCol,aRow]<>'A') and grid.Cells[aCol,aRow]<>'B') then begin
     // set a new valid value so user can just press RETURN to continue for example.
     NewValue := 'A';
     // another option is reverting to previous cell value (which is assumed to be valid)
     // NewValue := OldValue;
     raise Exception.Create('Only A or B are allowed here');
   end else begin
     // if no exception is raised, is assumed that value is valid, yet if necessary
     // final value can be changed by filling NewValue with a different value
      
     // computer knows better :)
     if grid.Cells[1,1]='A' then 
       NewValue := 'B' 
     else 
       NewValue := 'A';
   end;
 end;

end;</Delphi>

Sorting Columns or Rows

Property ColumnClickSorts allows grid to be sorted automatically when user clicks a column header. Clicking the same column many times switces the sort order. Default column sort images are shown to indicate which column was clicked.

In code you can use SortColRow() method. Its first parameter is a boolean value which indicates true if a column is to be sorted or false for a row, the next parameter is the column or row index, the next parameters are optional and selects subrange of rows (for column sorting) or columns (for row sorting) to be sorted, if the last parameters are not specified, the whole column or row is sorted. Sorting uses QuickSort algorithm, it could be changed if a descendant grid overrides the sort() method and calls doCompareCells for cell compare.

By default it sorts cell content as strings either in ascending or descending order which is selectable with property SortOrder, by default it uses ascending order. <Delphi>// sort column 3 in ascending order grid.SortColRow(true, 3);

// sort column 3 in descending order, skip fixed rows a top grid.SortOrder := soDescending; // or soAscending grid.SortColRow(true, 3, grid.FixedRows, grid.RowCount-1);</Delphi>

For custom sorting of numbers, dates, states, etc. StringGrid has the OnCompareCells event which users can handle for example this way: <Delphi>procedure TForm1.GridCompareCells(Sender: TObject; ACol, ARow, BCol, BRow: Integer; var Result: integer); begin

 // Result will be either <0, =0, or >0 for normal order.
 result := StrToIntDef(Grid.Cells[ACol,ARow],0)-StrToIntDef(Grid.Cells[BCol,BRow],0);
 // For inverse order, just negate the result (eg. based on grid's SortOrder).
 if StringGrid1.SortOrder = soDescending then
   result := -result;

end;</Delphi>

You can use OnCompareCells also when automatic column sorting is enabled through ColumnClickSorts property.

Selecting Records in a DBGrid using checkboxes

The objective is to be able to select arbitrary records in a dbgrid using checkboxes, the grid has the ability to show checkboxes automatically when it detects there are boolean fields, for other field types the user can manually choose the cbsCheckboxColumn ButtonStyle for the column. For this kind of columns the user just click the checkbox and the field content is modified accordingly.

But what happen if there is no such available field in our dataset? or we don't want the grid enter edit state when checking the checkbox?. Adding a fieldless column with ButtonStyle=cbsCheckboxColumn will show all checkboxes grayed and disabled because there is no field linked to this column and so nothing to modify. As we want to handle the checkbox state ourselves we need to store the state somewhere for each record. For this we can use the class TBookmarklist (defined in dbgrids.pas unit) where property CurrentRowSelected can tell if the current record is selected or not. By using dbgrid events OnCellClick and OnUserCheckboxState we can track the checkbox state.

Note this technique needs Lazarus r31148 or later which implements event OnUserCheckboxState.

<Delphi> ... uses ..., dbgrids, stdctrls, ...

type

 { TForm1 }
 TForm1 = class(TForm)
 ...
   procedure DBGrid1CellClick(Column: TColumn);
   procedure DBGrid1UserCheckboxState(sender: TObject; column: TColumn; var AState: TCheckboxState);
   procedure FormCreate(Sender: TObject);
   procedure FormDestroy(Sender: TObject);
 ...
 private
   RecList: TBookmarklist;
 ...
 end;

procedure TForm1.DBGrid1CellClick(Column: TColumn); begin

 if Column.Index=1 then
   RecList.CurrentRowSelected := not RecList.CurrentRowSelected;

end;

procedure TForm1.FormCreate(Sender: TObject); begin

 RecList := TBookmarkList.Create(DbGrid1);

end;

procedure TForm1.FormDestroy(Sender: TObject); begin

 RecList.Free;

end;

procedure TForm1.DBGrid1UserCheckboxState(sender: TObject; column: TColumn; var AState: TCheckboxState); begin

 if RecList.CurrentRowSelected then
   AState := cbChecked
 else
   AState := cbUnchecked;

end; </Delphi>