privatedcu.pas

Delphi Win32核心API参考光盘源码 本书包含了常用的Windows API函数

unit PrivateDcU;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;

type
  TForm1 = class(TForm)
    procedure FormPaint(Sender: TObject);
    procedure FormActivate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    procedure CreateParams(var Params: TCreateParams); override;
  end;

var
  Form1: TForm1;
  NewBrush,                  // a handle to a new brush
  OldBrush: HBRUSH;          // holds the old brush

implementation

{$R *.DFM}

procedure TForm1.CreateParams(var Params: TCreateParams);
begin
  {initialize the parameters with default values}
  inherited CreateParams(Params);

  {indicate that this window should have its own device context. comment
   this line out to see the effects}
  Params.WindowClass.style := Params.WindowClass.Style or CS_OWNDC;
end;

procedure TForm1.FormActivate(Sender: TObject);
var
  TempDC: HDC;         // a temporary device context handle
begin
  {retrieve a handle to the private device context for this window}
  TempDC := GetDC(Form1.Handle);

  {create a new brush and select it into this device context}
  NewBrush := CreateHatchBrush(HS_DIAGCROSS, clRed);
  OldBrush := SelectObject(TempDC, NewBrush);

  {release the device context. note that since we are dealing with a private
   device context, the new brush will remain within the device context.}
  ReleaseDC(Form1.Handle, TempDC);
end;

procedure TForm1.FormPaint(Sender: TObject);
var
  TempDC: HDC;           // a temporary device context handle
begin
  {retrieve a handle to the private device context}
  TempDC := GetDC(Form1.Handle);

  {draw a rectangle. note that we are not creating a new brush, so the
   rectangle should be filled with the default brush selected in a device
   context.  since this is a private device context, it will use the brush
   previously selected to fill the rectangle}
  Rectangle(TempDC, 0, 0, ClientWidth, ClientHeight);

  {release the device context}
  ReleaseDC(Form1.Handle, TempDC);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  {delete the brush}
  SelectObject(GetDC(Form1.Handle), OldBrush);
  DeleteObject(NewBrush);
end;

end.