IDE tricks

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Create a new file with Open file

You can create a new file and save it, or you can create a new file with filename and file type in one step: Just open file (Ctrl+o) and select a nonexistent filename. For example: unit1.pas. The IDE will ask you if it should be created.

Customize new unit / form

Since 0.9.27 you can right click on the 'New unit' (New form) speedbutton and set the file type that should be created. You can register more file types via the IDEIntf or the project templates package.

IDE macros

IDE Macros in paths and filenames

IDE directives

IDE directives

Getting the compiler command line parameters created by the IDE

You can copy the parameters from Project -> Compiler Options -> Show Options. Here the paths are relative to the project directory. So in most cases you can copy them without adjusting.

The parameters are also saved to the *.compiled file. For example if your project is called test1.lpi, then a test1.compiled is created. It is a simple text XML file, so you can just copy the options and adjust the paths to compile on another computer. The file is put into the same directory, where the executable is created.

For packages this works the same.

This way, you can compile your (hopefully working and bug free) code, outside of the Lazarus IDE.

Closing all editor files except one

Under GTK (available for Linux, macOS and FreeBSD) the source editor pages have a close button to the right of their page name. Press the Ctrl key while clicking on the button, closes all files except the clicked one.

Component palette

Finding a component in the palette

You know the component name, or part of it, but you don't know on which page it was? This tool finds it: Right click on any component in the palette to open the popup menu. Select 'View all' from the menu; this will pop open a dialog(also you can achieve it by pressing Ctrl+Alt+P). Enter the (partial) component name in the 'Find' box to filter the list.

Open the package of a component in the palette

Right click on the component to open the popup menu, then choose open package.

Find the source declaration of a component in the palette

Right click on the component to open the popup menu, then choose open unit.

My application freezes my Linux desktop while debugging

X (your desktop) can freeze, when an application that grabbed the mouse is stopped by gdb (the debugger).

Using a second X session

You can start a second X by:

  X :1 &

with Ctrl-Alt-F7 you switch to :0 and with Ctrl-Alt-F8 you switch to :1 after that you can start a second gnome session by:

  gnome-session --display=:1 &

Using VNC

You can use vncserver/client by installing tightvncserver or realvncserver. Start the server with:

  vncserver :1

AFAIK, a session is also started. You can connect to the vncserver with vncviewer.

Debug the application on the second server

In Lazarus, in the run parameters for your project, check "use display" and enter


Now your application will run on the second server, so when it is being debugged, only the second server will freeze (but that won't affect you since you are debugging on the first).

Compiling the IDE fast

Working on Lazarus itself means rebuilding the IDE many times. If you use the following tricks and have enough memory and a recent CPU, you should be able to recompile the IDE in a few seconds.

  • Put the Lazarus sources on a fast hard disk or solid state drive. Not on a slow network filesystem.
  • Install only needed packages.
  • Set USESVN2REVISIONINC=0 to skip the update of the file.

DebugLn of the IDE or a LCL application

The IDE writes many useful hints via DebugLn. You can get these this way:

  • Windows: start Lazarus with the command line parameter --debug-log=filename.txt.
  • Linux/FreeBSD/macOS/Solaris: just start Lazarus in a terminal.

This is a general LCL feature.

Finding the source file of an IDE window

  • Open the IDE window.
  • Press Ctrl+Shift+F1 to open the help editor.
  • Remember the window classname. Close the window.
  • Use Find In Files to find the source file of the class.

Opening a Terminal Windows from the IDE

Its often handy to be able to open a terminal in your current project's working directory. Maybe to use a revision control system like git or svn or for a host of other possible reasons. Here is how to add a menu item to Lazarus's Tool's menu. Thanks to taazz and other contributors to the forum thread.

  • Click Tools, Configure External Tools
  • Click 'Add' to add a new menu item (under Tools).
  • Set Title to (eg) "Open a Terminal"
  • Set Program File Name to the command on your system that opens a terminal, some suggestions below.
  • Set Parameters to what ever your terminal expects on the command line to open a specific directory and the Lazarus var that points there, $projPath().

Those last two vary quite a lot between systems, if you don't know the first, try looking at a list of running programs, the word 'terminal' is likely to feature. For the second, once you know the terminal's name, look up its man page or google.

Some examples include -

O.S. Program File Name Parameters
Ubuntu Mate mate-terminal --tab --working-directory=$projPath()
xfce exo-open --launch TerminalEmulator --working-directory $ProjPath()
KDE konsole --working-dir $projPath()
GNOME gnome-terminal --working-directory $projPath()
Mac (see below) /User/$HOME/bin/ttab cd $projPath()
Windows cmd.exe /k cd "$ProjPath()"
IDE Ext Tool

On the Mac, where everything is so much easier, all you have to do is:

  1. Install, its only 665 lines, use the path you installed it to instead of the example shown in the table above.
  2. Run it so you can tick its security to access the Accessibility feature.
  3. Then set the Lazarus Tools settings as described.
  4. Then, from within Lazarus, Tools->Open Terminal, then similar to 3) tick to allow Lazarus to access the Accessibility thingo.

On Windows, its also necessary to tick the "Show Console" as shown in the image on the right:

Object Inspector: Events: Frames: Jump to the source of an inherited event

The Object Inspector shows the events of inherited events as ClassName.MethodName. Double clicking will create a new event. Ctrl+Mouse click on the combobox will jump directly to the inherited method body, without creating a new method.

Events (Method properties) in the Object Inspector

Events (Method properties) are special properties, because they need as value a code address pointer, which does not exist at design time. That's why Lazarus uses the same trick as the Delphi IDE: Every method value can be type cast to TMethod, which contains Data (the object or class pointer) and the Code (the address pointer). At runtime both are set. But at design time the IDE sets Data to a special key value for its internal lookup table and sets Code to nil. This means:

  • At runtime when the program loads the .lfm file the real method (Data+Code) is used
  • At design time a method value can either be a real method (Data<>nil and Code<>nil) or a fake method (Data<>nil,Code=nil)
  • The compiler has for Delphi compatibility some specials about comparing method values.
  • The = and the <> operator only checks the Code, not the Data.

Do not use:

if OnMyEvent = NewValue then exit; // wrong, because it compares only Code

Because this only compares the Code. Use instead

if CompareMem(@FOnMyEvent, @NewValue, SizeOf(TMethod)) then exit; // correct, checking both Data and Code

Here is an example where the = operator fails:

  TMyClass = class
    FOnClick: TNotifyEvent;
    procedure SetOnClick(Value: TNotifyEvent);
    procedure Click(Sender: TObject);
    property OnClick: TNotifyEvent read FOnClick write SetOnClick;

procedure TMyClass.SetOnClick(Value: TNotifyEvent);
  if Value = FOnClick then exit; // bug, checks only for Code, not for data
  FOnClick := Value;

  a, b: TMyClass;
  a := TMyClass.Create;
  b := TMyClass.Create;
  a.OnClick := @a.Click;
  a.OnClick := @b.Click; // same code, but different data, a.OnClick still points to @a.Click;