线程执行后进度条为 NULL

Question

我有一个带有进度条的表单和一个将 xml 上传到服务器的按钮。 当按下按钮时，会创建一个新线程来创建一个套接字，然后它将数据以块的形式发送到服务器，同时它会更新进度条。 现在，当第二次按下上传按钮时，我遇到了访问冲突，并且在调试器中，进度条对象的地址为 NULL。 我不知道为什么进度条会被释放，所以如果有人有任何想法，我将不胜感激。

附：目标操作系统是windows P.S.2如果相同的代码在没有使用线程的情况下在主线程上运行，那么我似乎没有这个问题，即使我在线程中整体跳过进度条的使用，它也会在之后再次设置为 null第一次按下上传按钮。

线程构造函数：

__fastcall UploadRouteThread::UploadRouteThread(bool CreateSuspended) : TThread(CreateSuspended)
{
    this->OnTerminate = OnTerminateHandler;
    ioHandlerStack = new TIdIOHandlerStack();
    tcpClient = new TIdTCPClient();

    tcpClient->ReadTimeout = -1;
    tcpClient->UseNagle = true;

    tcpClient->IOHandler = ioHandlerStack;
    tcpClient->OnConnected = OnConnectedHandler;

}

OnTerminate 处理程序：

void __fastcall UploadRouteThread::OnTerminateHandler(TObject *Sender)
{
    TabbedwithNavigationForm->UploadButton->Text = "Upload";
    TabbedwithNavigationForm->UploadButton->Enabled = false;
    TabbedwithNavigationForm->ProgressBar->Visible = false;

    tcpClient->DisconnectNotifyPeer();

    ShowMessage("Data uploaded.");

    delete ioHandlerStack;
    delete tcpClient;

    TabbedwithNavigationForm->OptionButton->Enabled = true;
    TabbedwithNavigationForm->RetrieveRoutesButton->Enabled = true;
    TabbedwithNavigationForm->TrackButton->Enabled = true;
    TabbedwithNavigationForm->MediaButton->Enabled = true;
}

执行方法：

void __fastcall UploadRouteThread::Execute()
{
    FreeOnTerminate = true;
    tcpClient->Connect();
}

两个补充功能：

void __fastcall UploadRouteThread::SetHostPort(UnicodeString host, unsigned short port)
{
    tcpClient->Host = host;
    tcpClient->Port = port;
}

void __fastcall UploadRouteThread::SetXML(AnsiString xmlString)
{
    this->xmlString = xmlString;
}

OnConnect 处理程序：

void __fastcall UploadRouteThread::OnConnectedHandler(TObject *Sender)
{
    NextPacketSize nps;
    TIdBytes bytes;
    int chunks;
    int bytesLength;

    nps.PacketID = BasicPacket::DATA_UPLOAD;
    nps.size = xmlString.Length();

    tcpClient->IOHandler->WriteDirect(RawToBytes(&nps, sizeof(nps)), sizeof(NextPacketSize));
    bytes = RawToBytes(xmlString.c_str(), xmlString.Length());

    bytesLength = bytes.get_length();
    chunks = ceil(float(bytesLength) / 256.0);

    int previousSizeSent(0);
    for(int i = 1; i <= chunks; i++)
    {
        if(Terminated)
            break;
        int bytesToSend = 256;
        TByteDynArray byteDynArray;

        if((bytesToSend > bytesLength))
        {
              bytesToSend = bytesLength;
        }

        byteDynArray = bytes.CopyRange(previousSizeSent, bytesToSend);

        tcpClient->IOHandler->WriteDirect(ToBytes(byteDynArray, byteDynArray.get_length(), 0),
        byteDynArray.get_length());

        sent = (float(i) / float(chunks)) * 100;
        TThread::Synchronize(this, UpdateProgressBarInternal);

        previousSizeSent += bytesToSend;
        bytesLength -= bytesToSend;
    }
}

还有进度条的Update方法：

void __fastcall UploadRouteThread::UpdateProgressBarInternal()
{
    if(!TabbedwithNavigationForm->ProgressBar->Visible)
    {
        TabbedwithNavigationForm->ProgressBar->Visible = true;
        TabbedwithNavigationForm->ProgressBar->Max = 100;
    }

    TabbedwithNavigationForm->ProgressBar->Value = sent;
}

Answer 1

我在这段代码中看不到任何会导致 ProgressBar 指针变为NULL 的内容。因此，要么是您破坏了内存，要么是此处未显示的其他代码中的其他内容是罪魁祸首。无论哪种方式，要解决此问题，您可以在第一次运行线程之前在 IDE 调试器中运行您的应用程序并在 ProgressBar 变量上设置 Data Breakpoint。如果有东西改变了那个指针的值，断点就会被命中，你可以查看调用堆栈来弄清楚发生了什么。

话虽如此，您的帖子组织得不是很好。还有一种更简单的方法来处理分块 - 让 Indy 为您完成。它有一个OnWork 事件，可用于更新进度条。

试试这样的：

__fastcall UploadRouteThread::UploadRouteThread(String host, TIdPort port, AnsiString xmlString)
    : TThread(false)
{
    this->FreeOnTerminate = true;
    this->OnTerminate = OnTerminateHandler;
    this->xmlString = xmlString;

    tcpClient = new TIdTCPClient();
    tcpClient->Host = host;
    tcpClient->Port = port;
    tcpClient->UseNagle = true;
    tcpClient->OnWork = OnWorkHandler;
}

__fastcall UploadRouteThread::~UploadRouteThread()
{
    delete tcpClient;
}

void __fastcall UploadRouteThread::OnTerminateHandler(TObject *Sender)
{
    TabbedwithNavigationForm->UploadButton->Text = "Upload";
    TabbedwithNavigationForm->UploadButton->Enabled = false;
    TabbedwithNavigationForm->ProgressBar->Visible = false;

    if (FatalException)
        ShowMessage("Data not uploaded.");
    else
        ShowMessage("Data uploaded.");

    TabbedwithNavigationForm->OptionButton->Enabled = true;
    TabbedwithNavigationForm->RetrieveRoutesButton->Enabled = true;
    TabbedwithNavigationForm->TrackButton->Enabled = true;
    TabbedwithNavigationForm->MediaButton->Enabled = true;
}

void __fastcall UploadRouteThread::OnWorkHandler(TObject *ASender, TWorkMode AWorkMode, __int64 AWorkCount)
{
    if (Terminated)
        Sysutils::Abort();

    sent = (double(AWorkCount) * 100.0) / xmlString.Length();

    // consider using TThread::Queue() instead so that you don't block
    // the upload waiting for the UI to be updated...
    TThread::Synchronize(this, &UpdateProgressBarInternal);
}

void __fastcall UploadRouteThread::Execute()
{
    tcpClient->Connect();
    try
    {
        NextPacketSize nps;
        nps.PacketID = BasicPacket::DATA_UPLOAD;
        nps.size = xmlString.Length();
        tcpClient->IOHandler->Write(RawToBytes(&nps, sizeof(nps)));

        tcpClient->BeginWork(wmWrite, xmlString.Length());
        tcpClient->IOHandler->Write(RawToBytes(xmlString.c_str(), xmlString.Length()));
        tcpClient->EndWork(wmWrite);

        /* alternatively:
        TIdMemoryBufferStream *strm = new TIdMemoryBufferStream(xmlString.c_str(), xmlString.Length());
        try
        {
            // optional
            tcpClient->IOHandler->SendBufferSize = 256;

            // this calls (Begin|End)Work() internally...
            tcpClient->IOHandler->Write(strm, 0, false);
        }
        __finally
        {
            delete strm;
        }
        */
    }
    __finally
    {
        tcpClient->Disconnect();
    }
}

void __fastcall UploadRouteThread::UpdateProgressBarInternal()
{
    if (!TabbedwithNavigationForm->ProgressBar->Visible)
    {
        TabbedwithNavigationForm->ProgressBar->Visible = true;
        TabbedwithNavigationForm->ProgressBar->Max = 100;
    }

    TabbedwithNavigationForm->ProgressBar->Value = sent;
}