好奇一下。看来Object Pascal确实与Windows深入结合了。
unit Unit1;interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, ExtCtrls;const
UM_Test = WM_USER + 100;type
TForm1 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
procedure MyMessage(var Msg: TMessage); message UM_Test;
end;var
Form1: TForm1;implementation
{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
begin
Perform(UM_Test, 0, 0);
end;procedure TForm1.MyMessage(var Msg: TMessage);
begin
inherited;
ShowMessage(‘Hello‘);
end;end.
在message处理中和其他不一样的是inherited不会因为没有在祖先中找到一样的函数或者方法而将inherited失效，他会传入缺省的消息处理.
这里调用TFORM1的祖先的消息处理，由于tform和tcustomform没有这个实现，所以直接调用的是tcustomform的defaulthandle.（注意这个方法是对twincontrol的override）。
但是，如果本类重载了DefaultHandler函数，就会直接调用本类的DefaultHandler函数：
unit Unit1;interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, ExtCtrls;const
UM_Test = WM_USER + 100;type
TForm1 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
procedure MyMessage(var Msg: TMessage); message UM_Test;
procedure DefaultHandler(var Message); override;
end;var
Form1: TForm1;implementation
{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
begin
Perform(UM_Test, 0, 0);
end;procedure TForm1.DefaultHandler(var Message);
begin
with TMessage(Message) do
begin
if Msg = UM_Test then ShowMessage(‘DefaultHandler‘);
end;
inherited;
end;procedure TForm1.MyMessage(var Msg: TMessage);
begin
inherited;
ShowMessage(‘Hello‘);
end;end.
顺便再看看这样改写的效果：
procedure TForm1.DefaultHandler(var Message);
begin
with TMessage(Message) do
begin
if Msg = UM_Test then ShowMessage(‘DefaultHandler‘);
if Msg = WM_SETTEXT then ShowMessage(‘WM_SETTEXT‘);
end;
inherited;
end;
inherited在消息中的作用,码迷,mamicode.com