Question

我的应用在GET事件上发出FormShow命令，有时用户可能会按下Back并在线程启动后关闭表单但尚未完成，从而导致错误例如Thread Error: Invalid argument (22)或Thread Error: No such process (3)。

procedure TForm58.FormShow(Sender: TObject);
begin
    if Assigned(LListThread) then LListThread := nil;
    LListThread := TLoadListThread.Create;
    LListThread.OnTerminate := LoadListThreadTerminated;
    LListThread.Start;
end;

constructor TLoadListThread.Create;
begin
  inherited Create(True);
  FreeOnTerminate := True;
end;

procedure TLoadListThread.Execute;
begin
    if Form58.IdHTTP1.Connected then Form58.IdHTTP1.Disconnect;
    st := TStringList.Create;
    try
        ms := TMemoryStream.Create;
        Synchronize(
        procedure
        begin
            Form58.Label1.Text := 'Loading...';
        end);
        try
            Form58.IdHTTP1.Get(urlserver,ms);
            ms.Position := 0;
            st.LoadFromStream(ms, TEncoding.UTF8);
        finally
            ms.Free;
        end;
        // Do something with st
    finally
        st.Free;
    end;
end;

procedure TForm58.LoadListThreadTerminated(Sender: TObject);
begin
    if IdHTTP1.Tag = 1 then
    begin
        LListThread := nil;
        Form58.Close;
    end else
    begin
      LListThread := nil;
      if TThread(Sender).FatalException = nil then
      // Do something
      else
      // Do otherthing
    end;
end;

procedure TForm58.CloseButtonClick(Sender: TObject);
begin
  if Assigned(LListThread) then
  begin
    IdHTTP1.Tag := 1;
    LListThread.Terminate;
  end else Form58.Close;
end;

procedure TForm58.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  if Assigned(LListThread) then
  begin
    LListThread.Destroy;
    LListThread := nil;
  end;
  try
    // Do something
  finally
    Action := TCloseAction.caFree;
  end;
end;

我知道我制作的线程开始/结束逻辑很糟糕，如何改进它并删除显示的错误消息？

Answer 1

当准备关闭表单时，如果线程仍然在运行，那么你发信号通知它终止，但是你没有等待它完全终止，然后你在表单中明确地销毁线程对象实际上即使您使用FreeOnTerminate=True也会关闭。

在明确销毁线程对象之前，您应该调用TThread.WaitFor()，但在使用FreeOnTerminate=True时这不起作用，这会导致您看到的错误类型。除此之外，如果线程仍在运行，TThread析构函数会自行调用WaitFor()，并且您正在显式地销毁线程对象。无论哪种方式，都会导致错误。

所以，你需要：

设置FreeOnTerminate=False，然后等待线程完全终止，然后再明确销毁它。
设置FreeOnTerminate=True并且根本不要手动销毁线程对象，也不要关闭该表单直到线程终止。

我还建议覆盖线程的虚拟TerminatedSet()方法来设置一个标志，然后可以在线程内检查以中止GET请求，例如在{{1事件。

使用TIdHTTP.OnWork时尝试这样的事情：

FreeOnTerminated=True

type
  TLoadListThread = class(TThread)
  private
    FUrl: string;
    FOnLoading: TNotifyEvent;
    DoAbort: Boolean;
    procedure CheckAbort;
    procedure DoLoading;
    procedure HTTPWork(ASender: TObject; AWorkMode: TWorkMode; AWorkCount: Int64);
  protected
    procedure TerminatedSet; override;
  public
    constructor Create(const AUrl: String);
    property OnLoading: TNotifyEvent read FOnLoading write FOnLoading;
  end;

constructor TLoadListThread.Create(const AUrl: String);
begin
  inherited Create(True);
  FreeOnTerminate := True;
  FUrl := AUrl;
end;

procedure TLoadListThread.CheckAbort;
begin
  if DoAbort then SysUtils.Abort;
end;

procedure TLoadListThread.DoLoading;
begin
  if Assigned(FOnLoading) then FOnLoading(Self);
end;

procedure TLoadListThread.HTTPWork(ASender: TObject; AWorkMode: TWorkMode; AWorkCount: Int64);
begin
  CheckAbort;
end;

procedure TLoadListThread.TerminatedSet;
begin
  inherited;
  DoAbort := True;
end;

procedure TLoadListThread.Execute;
var
  HTTP: TIdHTTP;
begin
  HTTP := TIdHTTP.Create;
  try
    st := TStringList.Create;
    try
      ms := TMemoryStream.Create;
      try
        if Assigned(FOnLoading) then Synchronize(DoLoading);
        CheckAbort;
        HTTP.Get(FUrl, ms);
        ms.Position := 0;
        st.LoadFromStream(ms, TEncoding.UTF8);
      finally
        ms.Free;
      end;
      CheckAbort;
      // Do something with st
    finally
      st.Free;
    end;
  finally
    HTTP.Free;
  end;
end;

或者，当使用private procedure CloseOnTerminated(Sender: TObject); procedure TForm58.FormShow(Sender: TObject); begin StopLoadListThread; LListThread := TLoadListThread.Create(urlserver); LListThread.OnLoading := LoadListThreadLoading; LListThread.OnTerminate := LoadListThreadFinished; LListThread.Start; end; procedure TForm58.StopLoadListThread; begin if Assigned(LListThread) then begin LListThread.OnLoading := nil; LListThread.OnTerminate := nil; LListThread.Terminate; LListThread := nil; end; end; procedure TForm58.LoadListThreadLoading(Sender: TObject); begin Label1.Text := 'Loading...'; end; procedure TForm58.LoadListThreadFinished(Sender: TObject); begin if LListThread.FatalException = nil then // Do something else // Do something else LListThread := nil; end; procedure TForm58.CloseOnTerminated(Sender: TObject); begin LListThread := nil; Close; end; procedure TForm58.CloseButtonClick(Sender: TObject); begin Close; end; procedure TForm58.FormClose(Sender: TObject; var Action: TCloseAction); begin if Assigned(LListThread) then begin LListThread.OnTerminate := CloseOnTerminated; LListThread.Terminate; Action := TCloseAction.caNone; end else begin // Do something Action := TCloseAction.caFree; end; end;时：

FreeOnTerminated=False

type
  TLoadListThread = class(TThread)
  private
    FUrl: string;
    FOnLoading: TNotifyEvent;
    DoAbort: Boolean;
    procedure CheckAbort;
    procedure DoLoading;
    procedure HTTPWork(ASender: TObject; AWorkMode: TWorkMode; AWorkCount: Int64);
  protected
    procedure TerminatedSet; override;
  public
    constructor Create(const AUrl: String);
    property OnLoading: TNotifyEvent read FOnLoading write FOnLoading;
  end;

constructor TLoadListThread.Create(const AUrl: String);
begin
  inherited Create(True);
  FreeOnTerminate := False;
  FUrl := AUrl;
end;

procedure TLoadListThread.CheckAbort;
begin
  if DoAbort then SysUtils.Abort;
end;

procedure TLoadListThread.DoLoading;
begin
  if Assigned(FOnLoading) then FOnLoading(Self);
end;

procedure TLoadListThread.HTTPWork(ASender: TObject; AWorkMode: TWorkMode; AWorkCount: Int64);
begin
  CheckAbort;
end;

procedure TLoadListThread.TerminatedSet;
begin
  inherited;
  DoAbort := True;
end;

procedure TLoadListThread.Execute;
var
  HTTP: TIdHTTP;
begin
  HTTP := TIdHTTP.Create;
  try
    st := TStringList.Create;
    try
      ms := TMemoryStream.Create;
      try
        if Assigned(FOnLoading) then Synchronize(DoLoading);
        CheckAbort;
        HTTP.Get(FUrl, ms);
        ms.Position := 0;
        st.LoadFromStream(ms, TEncoding.UTF8);
      finally
        ms.Free;
      end;
      CheckAbort;
      // Do something with st
    finally
      st.Free;
    end;
  finally
    HTTP.Free;
  end;
end;

如何使用Indy HTTP Get命令正确终止线程？

1 个答案: