Application.HandleMessage与Application.ProcessMessage

HandleMessage：

　　　　HandleMessage中断应用程序的执行，以便Windows可以在将控制权返回给应用程序之前处理来自Windows消息队列的单个消息。

如果消息队列为空，则HandleMessage生成OnIdle事件并启动更新应用程序中的操作的过程。

　　　　注意：如果应用程序空闲，HandleMessage可能需要很长时间才能返回。

　　　　因此，在等待基于消息的事务时，不要在处理优先级操作时调用HandleMessage。相反，在处理的不仅仅是消息时调用ProcessMessages。

ProcessMessage：

　　 ProcessMessages不允许应用程序空闲，而HandleMessage则允许。

unit Unit1;

interface

uses

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

  Dialogs, StdCtrls;

type

  TForm1 = class(TForm)

    Button1: TButton;

    Button2: TButton;

    procedure FormCreate(Sender: TObject);

    procedure Button1Click(Sender: TObject);

    procedure Button2Click(Sender: TObject);

    procedure FormShow(Sender: TObject);

  private

    { Private declarations }

    procedure MyIdleHandler(Sender: TObject; var Done: Boolean);

  public

    { Public declarations }

  end;

var

  Form1: TForm1;

implementation

{$R *.dfm}

var

{ Global variables to show the order of events }

  XPos, YPos, Delta: integer;

procedure StatusMsg(

  MyForm : TForm1; Canvas : TCanvas; Message : string; Bkg : Boolean);

begin

  if not bkg then

    Canvas.Font.Style := [fsBold]; {Foreground messages are in bold type. }

  Canvas.TextOut(XPos, YPos, Message);

  if not bkg then

    Canvas.Font.Style := [];

  { Change Xpos and YPos to prepare for the next message. }

  Ypos := Ypos + Delta;

  if YPos >= MyForm.ClientHeight - 10 then

  begin

    YPos := 10;

    Xpos := Xpos + 180;

  end;

  if (Xpos >= MyForm.ClientWidth - 100) then

  begin

    if (Canvas.Font.Color = clRed) then

      Canvas.Font.Color := clBlack

    else

      Canvas.Font.Color := clRed;

    Xpos := 10;

  end;

end;

procedure TForm1.FormCreate(Sender: TObject);

begin

  Button1.Caption := 'Do not yield';

  Button2.Caption := 'Handle Message';

  Application.OnIdle:= MyIdleHandler;

  XPos := 10;

  YPos := 10;

  Delta := Abs(Canvas.Font.Height) + 1;

end;

procedure TForm1.Button1Click(Sender: TObject);

var

  I, J, X, Y: Word;

begin

  StatusMsg(

    Form1, Canvas, 'The synchronous handler is starting', False);

  I := 0;

  J := 0;

  while I < 10 do

  begin

    Randomize;

    while J < 10 do

    begin

      Y := Random(J);

      Inc(J);

    end;

    X := Random(I);

    Inc(I);

  end;

  StatusMsg(

    Form1, Canvas, 'The synchronous handler is done', False);

end;

procedure TForm1.Button2Click(Sender: TObject);

var

  I, J, X, Y: Word;

begin

//同时执行onIdle事件和当前任务

 StatusMsg(

    Form1, Canvas, 'The asynchronous handler is starting', False);

  I := 0;

  J := 0;

  while I < 100 do

  begin

    Randomize;

    while J < 10 do

    begin

      Y := Random(J);

      Inc(J);

    end;

    X := Random(I);

    Inc(I);

    { yield to OnIdle or other messages }

//    PostMessage(Handle,WM_PAINT,0,0);  假如消息队列不是空，则不会生成onIdle事件

    Application.HandleMessage;

  end;

  StatusMsg(

    Form1, Canvas, 'The asynchronous handler is done', False);

end;

procedure TForm1.FormShow(Sender: TObject);

begin

end;

{ TForm1 }

procedure TForm1.MyIdleHandler(Sender: TObject; var Done: Boolean);

begin

    StatusMsg(

    Form1, Canvas, 'This represents a background process.', True);

end;

end.

巴特西

Application.HandleMessage与Application.ProcessMessage

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