学習メッセージ(7):OnMessageは対応するメッセージキュー内のメッセージのみ

Perform、SendMessageはフォームプロセスに直接メッセージを送信します.
PostMessageはメッセージをメッセージキューに入れる.
なぜならOnMessageはキュー内のメッセージのみを受信し、
だからPerform、SendMessageが送ったメッセージは、OnMessageには届かない.
テストは次のとおりです.
コードファイル:

unit Unit1;



interface



uses

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

  Dialogs, AppEvnts, StdCtrls;



type

  TForm1 = class(TForm)

    ApplicationEvents1: TApplicationEvents;

    Button1: TButton;

    Button2: TButton;

    Button3: TButton;

    procedure ApplicationEvents1Message(var Msg: tagMSG; var Handled: Boolean);

    procedure Button1Click(Sender: TObject);

    procedure Button2Click(Sender: TObject);

    procedure Button3Click(Sender: TObject);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



{  ApplicationEvents1.OnMessage  ;  }

procedure TForm1.ApplicationEvents1Message(var Msg: tagMSG;

  var Handled: Boolean);

begin

  if Msg.message = WM_LBUTTONDBLCLK then

  begin

    ShowMessage('WM_LBUTTONDBLCLK');

    Handled := True;

  end;

end;



{  Perform   WM_LBUTTONDBLCLK  ; OnMessage  }

procedure TForm1.Button1Click(Sender: TObject);

begin

  Self.Perform(WM_LBUTTONDBLCLK, 0, 0);

end;



{  SendMessage   WM_LBUTTONDBLCLK  ; OnMessage  }

procedure TForm1.Button2Click(Sender: TObject);

begin

  SendMessage(Self.Handle, WM_LBUTTONDBLCLK, 0, 0);

end;



{  PostMessage   WM_LBUTTONDBLCLK  ; OnMessage  }

procedure TForm1.Button3Click(Sender: TObject);

begin

  PostMessage(Self.Handle, WM_LBUTTONDBLCLK, 0, 0);

end;



end.


 
   

フォームファイル:

object Form1: TForm1

  Left = 0

  Top = 0

  Caption = 'Form1'

  ClientHeight = 145

  ClientWidth = 255

  Color = clBtnFace

  Font.Charset = DEFAULT_CHARSET

  Font.Color = clWindowText

  Font.Height = -11

  Font.Name = 'Tahoma'

  Font.Style = []

  OldCreateOrder = False

  PixelsPerInch = 96

  TextHeight = 13

  object Button1: TButton

    Left = 8

    Top = 97

    Width = 75

    Height = 25

    Caption = 'Button1'

    TabOrder = 0

    OnClick = Button1Click

  end

  object Button2: TButton

    Left = 89

    Top = 97

    Width = 75

    Height = 25

    Caption = 'Button2'

    TabOrder = 1

    OnClick = Button2Click

  end

  object Button3: TButton

    Left = 170

    Top = 97

    Width = 75

    Height = 25

    Caption = 'Button3'

    TabOrder = 2

    OnClick = Button3Click

  end

  object ApplicationEvents1: TApplicationEvents

    OnMessage = ApplicationEvents1Message

    Left = 128

    Top = 24

  end

end