QProgressBar 没有显示进度?

问题描述

我在更新进度条时的第一个天真是在我的循环中包含以下几行进行处理，制作如下所示:

My first naive at updating my progress bar was to include the following lines in my loop which is doing the processing, making something like this:

while(data.hasMoreItems())
{
    doSomeProcessing(data.nextItem())

    //Added these lines but they don't do anything
    ui->progressBar->setValue(numberProcessed++);
    ui->progressBar->repaint();
}

我认为添加 repaint() 会使执行在更新 GUI 时暂停，但显然这不是那么简单.看完问题后:

I thought adding the repaint() would make the execution pause while it updated the GUI, but apparently it's not that simple. After looking at the questions:

QProgressBar 错误
进度条未显示进度

看起来我将不得不将数据处理放在不同的线程中，然后将来自数据处理线程的信号连接到 GUI 线程以更新进度条.我对 GUI 和线程缺乏经验，我想知道是否有人可以指出我正确的方向，即我应该为此考虑使用哪些 Qt 类.我想我需要一个 QThread 对象，但我一直在查看 QProgressBar 文档，但它没有提出线程的主题.

it looks like I'm going to have to put the data processing in a different thread and then connect a signal from the data processing thread to the GUI thread to update the progressbar. I'm rather inexperienced with GUIs and threads and I was wondering if anyone could just point me in the right direction, ie what Qt classes should I be looking at using for this. I'd guess I need a QThread object but I've been looking through the QProgressBar documentation but it doesn't bring up the topic of threading.

推荐答案

正如@rjh 和@Georg 所指出的，本质上有两种不同的选择:

As @rjh and @Georg have pointed out, there are essentially two different options:

1. 使用 QApplication::processEvents() 强制处理事件, 或
2. 创建一个线程，它发出可用于更新进度条

1. Force processing of events using QApplication::processEvents(), OR
2. Create a thread that emits signals that can be used to update the progress bar

如果您正在进行任何非平凡的处理，我建议将处理移至线程.

If you're doing any non-trivial processing, I'd recommend moving the processing to a thread.

要了解线程的最重要的一点是，除了主 GUI 线程(您不会启动也不会创建)之外，您永远无法直接从线程内更新 GUI.

The most important thing to know about threads is that except for the main GUI thread (which you don't start nor create), you can never update the GUI directly from within a thread.

QObject::connect() 的最后一个参数 是一个 Qt::ConnectionType 枚举，默认情况下考虑是否涉及线程.

The last parameter of QObject::connect() is a Qt::ConnectionType enum that by default takes into consideration whether threads are involved.

因此，您应该能够创建一个简单的 QThread 子类来进行处理:

Thus, you should be able to create a simple subclass of QThread that does the processing:

class DataProcessingThread : public QThread
 {

 public:
     void run();
 signals:
     void percentageComplete(int);
 };

 void MyThread::run()
 {
    while(data.hasMoreItems())
    {
      doSomeProcessing(data.nextItem())
      emit percentageCompleted(computePercentageCompleted());
    }
 }

然后在您的 GUI 代码中的某处:

And then somewhere in your GUI code:

DataProcessingThread dataProcessor(/*data*/);
connect(dataProcessor, SIGNAL(percentageCompleted(int)), progressBar, SLOT(setValue(int));
dataProcessor.start();

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