学习官方示例 - TApplication.OnMessage

本例演示了一个消息的定义、发送和接受的过程.

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本例效果图:

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代码文件:

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unit Unit1;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls;



type

  TForm1 = class(TForm)

    Button1: TButton;

    procedure FormCreate(Sender: TObject);

    procedure Button1Click(Sender: TObject);

  private

    procedure AppMessage(var Msg: TMsg; var Handled: Boolean);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



const WM_MyMessage = WM_USER + 2000;



procedure TForm1.FormCreate(Sender: TObject);

begin

  Application.OnMessage := AppMessage;

  Button1.Caption := '发送自定义消息';

end;



procedure TForm1.AppMessage(var Msg: TMsg; var Handled: Boolean);

var msgStr: String;

begin

  if Msg.hwnd = Application.Handle then

  begin

    if Msg.message = WM_MyMessage then

    begin

      msgStr:= PChar(Msg.lParam);

      ShowMessage(msgStr);

      Handled := True;

    end;

  end;

end;



procedure TForm1.Button1Click(Sender: TObject);

const lParam: PChar = '来自定义消息';

begin

  PostMessage(Application.Handle, WM_MyMessage, 0, Integer(lParam));

end;



end.


 
   

窗体文件:

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object Form1: TForm1

  Left = 0

  Top = 0

  Caption = 'Form1'

  ClientHeight = 117

  ClientWidth = 225

  Color = clBtnFace

  Font.Charset = DEFAULT_CHARSET

  Font.Color = clWindowText

  Font.Height = -11

  Font.Name = 'Tahoma'

  Font.Style = []

  OldCreateOrder = False

  Position = poDesktopCenter

  OnCreate = FormCreate

  PixelsPerInch = 96

  TextHeight = 13

  object Button1: TButton

    Left = 48

    Top = 48

    Width = 129

    Height = 25

    Caption = 'Button1'

    TabOrder = 0

    OnClick = Button1Click

  end

end