子类化窗口辅助类NativeWindow

子类化窗口在高级开发中的重要利器。受c#中NativeWindow的启发，实现了下面这样一个简单的类，来帮助更容易地对窗口实现子类化。

unit NativeWindow;

interface

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

Type  TzwNativeWindow = class  private    m_OldWinProc:FARPROC  ;    m_NewWinProc:FARPROC  ;    m_Handle:THandle;  protected    procedure WndProc(var Message: TMessage); virtual;  public    constructor Create;    destructor Destroy;override;    procedure AssignHandle(WndHandle:THandle);    procedure ReleaseHandle;    property Handle:THandle read m_Handle;  end;

implementation

{ TzwNativeWindow }

procedure TzwNativeWindow.AssignHandle(WndHandle: THandle);begin  if (m_Handle<>WndHandle) then  begin    ReleaseHandle;  end;  m_Handle := WndHandle;  m_NewWinProc := MakeObjectInstance (WndProc );  m_OldWinProc := pointer(GetWindowLong (m_Handle ,GWL_WNDPROC ));  SetWindowLong(m_Handle , GWL_WNDPROC, LongInt(m_NewWinProc));end;

constructor TzwNativeWindow.Create;begin  m_Handle := INVALID_HANDLE_VALUE;  m_OldWinProc := nil;  m_NewWinProc := nil;end;

destructor TzwNativeWindow.Destroy;begin  ReleaseHandle;  inherited;end;

procedure TzwNativeWindow.ReleaseHandle;begin  if (m_Handle<>INVALID_HANDLE_VALUE) then  try    SetWindowLong(m_Handle,GWL_WNDPROC,LongInt(m_OldWinProc));  finally    m_Handle := INVALID_HANDLE_VALUE;    m_OldWinProc := nil;    m_NewWinProc := nil;  end;end;

procedure TzwNativeWindow.WndProc(var Message: TMessage);begin  with Message do  begin    Result := CallWindowProc(m_OldWinProc , m_Handle , Msg, wParam, lParam);  end;end;

end.