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How to use a TControlCanvas in a component

   
type
  TScrollingPaintBox = class(TScrollingWinControl)
  private
    FCanvas: TCanvas;
  public
    constructor Create(aOwner: TComponent); override;
    destructor Destroy; override;
    property Canvas: TCanvas read FCanvas;
  end;

constructor TScrollingPaintBox.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FCanvas := TControlCanvas.Create;
  TControlCanvas(FCanvas).Control := Self;
end;

destructor TScrollingPaintBox.Destroy;
begin
  FCanvas.Free;
  inherited Destroy;
end;

A TControlCanvas is important because it creates a DC (device context) that belongs to the HWND of the control. Also, override is important on your constructor and destructor to ensure that they are actually called.

Original resource: The Delphi Pool
Author: Unknown
Added: 2009-08-12
Last updated: 2009-08-12

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