等待线程，而不冻结应用程序 [英] Wait for thread without freezing the application

问题描述

我试图把一个indy TIdHttp放在一个线程中，
我已经尝试过：

I'm trying to put an indy TIdHttp in a thread, I have tried this :

type
  TSendThread = class(TThread)
  private
    { Private declarations }
  protected
    procedure Execute; override;
  public
    http : TIdHTTP;
    URL : String;
    Method : String;
    property ReturnValue;
  end;

procedure TSendThread.Execute;
begin
  form1.Memo1.lines.Add(http.Get(URL));
  ReturnValue := 1;
end;

主要内容：

procedure TForm1.Button1Click(Sender: TObject);
var t : TSendThread;
begin
  t := TSendThread.Create(true);
  t.URL := 'http://www.url.com/';
  t.http := http;
  t.Start;
  showmessage(IntToStr(t.ReturnValue));
end;

我的问题是下一个指令执行（showmessage），而不需要等待线程完成，我试图使用WaitFor，但它冻结了应用程序。

My problem here is that the next instruction gets executed(showmessage) without waiting the thread to be done, i tried to use the "WaitFor" but it freezes the application.

还有其他解决方法吗？

Is there any other workaround?

谢谢。

推荐答案

使用 TThread.OnTerminate 事件知道线程何时完成：

Use the TThread.OnTerminate event to know when the thread has finished:

type
  TSendThread = class(TThread)
  private
    http : TIdHTTP;
    Line: string;
    procedure AddLine;
  protected
    procedure Execute; override;
  public
    constructor Create; reintroduce;
    destructor Destroy; override;
    URL : String;
    Method : String;
    property ReturnValue;
  end;

constructor TSendThread.Create;
begin
  inherited Create(True);
  FreeOnTerminate := True;
  http := TIdHTTP.Create;
end;

destructor TSendThread.Destroy;
begin
  http.Free;
  inherited;
end;

procedure TSendThread.Execute;
begin
  Line := http.Get(URL);
  Synchronize(AddLine);
  ReturnValue := 1;
end;

procedure TSendThread.AddLine;
begin
  Form1.Memo1.Lines.Add(Line);
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  t : TSendThread;
begin
  t := TSendThread.Create;
  t.URL := 'http://www.url.com/';
  t.OnTerminate := ThreadTerminated;
  t.Start;
end;

procedure TForm1.ThreadTerminated(Sender: TObject);
begin
  ShowMessage(IntToStr(TSendThread(Sender).ReturnValue));
end;

如果要使用循环等待线程完成，而不阻止UI您可以这样做：

If you want to use a loop to wait for the thread to finish, without blocking the UI, then you can do it like this:

constructor TSendThread.Create;
begin
  inherited Create(True);
  //FreeOnTerminate := True; // <-- remove this
  http := TIdHTTP.Create;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  t : TSendThread;
  h : THandle;
begin
  t := TSendThread.Create;
  try
    t.URL := 'http://www.url.com/';
    t.Start;
    h := t.Handle;
    repeat
      case MsgWaitForMultipleObjects(1, h, 0, INFINITE, QS_ALLINPUT) of
        WAIT_OBJECT_0:   Break;
        WAIT_OBJECT_0+1: Application.ProcessMessages;
        WAIT_FAILED:     RaiseLastOSError;
      else
        Break;
      end;
    until False;
    ShowMessage(IntToStr(t.ReturnValue));
  finally
    t.Free;
  end;
end;

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