Cocoa Internals

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Revision as of 15:56, 12 November 2015 by Sekelsenmat (talk | contribs)

The page is about Cocoa Widgetset internal implementation. The page should be useful for Cocoa widgetset developers (maintainers and/or constributors) as well as any developers who need to use Cocoa specific API.

Other Interfaces

Platform specific Tips

Interface Development Articles

LCL specific ObjC classes

In order to control and handle an NSView's behavior LCL uses decedent classes from standard Cocoa controls. I.e. for NSWindow TCocoaWindow is introduced. The decedent are used for the purpose of "overriding" default class implementation, where it is needed. In some cases using delegate classes is not enough.


  • Window handle (HWND) is always NSView.
    • TCustomWSForm it is content NSView.
    • Any control that has scroll bars (i.e. TCustomWSList) the it its the embedding NSScrollView (TCocoaScrollView)
LCL Control Cocoa class Notes
TMemo NSTextView inside a NSScrollView -

Code Style

The following requirement applies for Cocoa widgetset. Other widgetset my be following some other rules (historically), but in general LCL follows the same requirements.

  • Operators Keep the operator separated by spaces between operands
 A := B; 
 A := B * C;
  • Blocks The main rule is to make 2 character spacing from the code block start. Begin / Else should start on a new line.
procedure B;
  if A then // 2 character spacing from begin
    Start Here // 2 character spacing from begin
    Next Line
    Another Line
  • Standard Function Name please keep naming in ProperCase. Reserved words should be lower case. Name of (global/local) variables and fields should match declaration. (local variables should start with lower case)
 if not Assigned(A) then
   Result := nil;

Themed Drawing / Custom Controls

HITheme API is deprecated by Apple together with Carbon. It's still available in OSX, but for i386 only. Presumably will be completely removed on 64-bit only OSX.

However, some LCL controls cannot be mapped to existing Cocoa provided controls and thus might require some "custom drawing". The drawing should look system native though. In order to achieve that NSCell family could be used. NSCell allows to draw (hit-test and as well as handle user input) for OSX native elements. If Apple to change appears of controls (cells), the LCL application would "pick-up" the look automatically.

In order to be drawn NSCells requires a present of NSView, thus it's hard to use them forthe implementation of LCL TTheme APIs

Example of NSCell usage is CocoaStatusBar drawing


NSFont class provides a number of class methods to get proper system font without selecting the font by name. The same of getting system-native font size.