如何使一个Mutlithreded idhttp调用在StringList上工作

Question

我是Threads的新手,我有一个List包含一个字符串.我的目标是让多个线程对这个List工作,这个代码只针对一个线程,因为我现在正在学习,但是当我按下开始按钮时我得到了AV.

type
  TDemoThread = class(TThread)
  private
    procedure Abort;
  protected
    procedure Execute; override;
  public
    List: TStringList;
  end;

procedure TfrmMain.StartButton1Click(Sender: TObject);
var
  i: integer;
  List: Tstrings;
begin
  for i := 0 to memo1.Lines.Count - 1 do
  begin
    List := TStringList.Create;
    List.Add(memo1.Lines.Strings[i]);
  end;

  Thread := TDemoThread.Create(True);
  Thread.FreeOnTerminate := True;
  Thread.Start;
end;

procedure TDemoThread.Execute;
var
  lHTTP: TIdHTTP;
  i: integer;
  X: Tstrings;
begin
  inherited;
  if Terminated then
    Exit;

  lHTTP := TIdHTTP.Create(nil);
  X := TStringList.Create;
  lHTTP.ReadTimeout := 30000;
  lHTTP.HandleRedirects := True;

  for i := 0 to List.Count - 1 do
    try
      X.Text := lHTTP.Get('https://instagram.com/' + List.Strings[i]);
      S := ExtractDelimitedString(X.Text);
      X.Clear;
      TThread.Synchronize(nil,
        procedure
        begin
          frmMain.Memo2.Lines.Add(List.Strings[i] + ' : ' + S);
        end);
    finally
    end;
end;

Answer 1

您的问题是您永远不会分配给List线程类的成员:

type
  TDemoThread = class(TThread)
  private
    procedure Abort;
  protected
    procedure Execute; override;
  public
    List: TStringList; <-- never assigned to, hence always nil
  end;

因此访问违规.

看起来你正试图将内容传递memo1给线程.我会那样做:

type
  TDemoThread = class(TThread)
  private
    FData: TStringList;
  protected
    procedure Execute; override;
  public
    constructor Create;
    destructor Destroy; override;
  end;

constructor TDemoThread.Create(Data: TStrings);
begin
  inherited Create(False);
  FData := TStringList.Create;
  FData.Assign(Data);
  FreeOnTerminate := True;
end;

destructor TDemoThread.Destroy;
begin
  FData.Free;
  inherited;
end;

procedure TDemoThread.Execute;
var
  lHTTP: TIdHTTP;
  i: integer;
  X: TStrings;
begin
  inherited;
  if Terminated then
    Exit;

  lHTTP := TIdHTTP.Create(nil);
  X := TStringList.Create;
  lHTTP.ReadTimeout := 30000;
  lHTTP.HandleRedirects := True;

  for i := 0 to FData.Count - 1 do
    try
      X.Text := lHTTP.Get('https://instagram.com/' + FData[i]);
      S := ExtractDelimitedString(X.Text);
      X.Clear;
      TThread.Synchronize(nil,
        procedure
        begin
          frmMain.Memo2.Lines.Add(FData[i] + ' : ' + S);
        end);
    finally
    end;
end;

procedure TfrmMain.StartButton1Click(Sender: TObject);
begin
  TDemoThread.Create(memo1.Lines);
end;

创建暂停然后立即启动是没有意义的.它也不允许在FreeOnTerminate线程启动后保持对线程的引用,所以我删除了它.

TDemoThread.Execute泄漏中的代码,除非您仅在ARC平台上运行.尝试/终于毫无意义.并且您不需要字符串列表来容纳单个字符串string.假设您没有使用ARC,它应该是:

procedure TDemoThread.Execute;
var
  lHTTP: TIdHTTP;
  i: integer;
  S: string;
begin
  if Terminated then
    Exit;

  lHTTP := TIdHTTP.Create(nil);
  try
    lHTTP.ReadTimeout := 30000;
    lHTTP.HandleRedirects := True;

    for i := 0 to FData.Count - 1 do
    begin
      S := ExtractDelimitedString(lHTTP.Get('https://instagram.com/' + FData[i]));
      TThread.Synchronize(nil,
        procedure
        begin
          frmMain.Memo2.Lines.Add(FData[i] + ' : ' + S);
        end);
    end;
  finally
    lHTTP.Free;
  end;
end;