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Sometimes, a class or object is missing this one little property or function we need. So how do we add a property or function to an existing class or object?
In this example I add the property "Selected" to a "TPanel".
This is a boolean property, but we could easily do with with a procedure or function as well.
In the beginning of your code (I usually place this either before the TForm definition, or in a separate unit):
TPanel = class(ExtCtrls.TPanel)
public
Selected:boolean;
end;
Now this property exists for every TPanel in this unit and can be read or assigned to.
Note: do not forget to add the phrase "public".
You can set the default value in the constructor like so:
TPanel = class(ExtCtrls.TPanel)
public
Selected:boolean;
constructor Create(AOwner:TComponent); override;
end;
...
// Overriding Create Constructor - for example set some default values and event handlers
constructor TPanel.Create(AOwner:TComponent);
begin
inherited;
// Set initial value for example ...
Selected := false;
end;
Adding a function or procedure is easy as well:
TPanel = class(ExtCtrls.TPanel)
public
Selected:boolean;
procedure DoSomething;
end;
...
procedure TPanel.DoSomething;
begin
...
end;
This way we do not have to abuse existing properties (eg. Tag), or fumble with all kinds of linked lists, and add convenient functions as well.