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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.
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