使用BackgroundWorker更新GUI [英] Update GUI using BackgroundWorker

问题描述

我一直在搜索，发现执行后台工作和更新GUI的一种好方法是使用后台工作程序.但是，执行此(愚蠢的)小任务(从1到10000计数)不会更新标签内容，而是打印到调试！ (当然，这只是另一个项目的解决方案……)

I've been searching and found that a good way to perform background work and update the GUI is using background workers. However, doing this (stupid) little task (counting from 1 to 10000) it doesn't update the label content but prints to the debug! (This is just a spike solution for another project of course...)

代码如下:

public partial class MainWindow : Window
{
    BackgroundWorker bw = new BackgroundWorker();

    public MainWindow()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, RoutedEventArgs e)
    {

        bw.DoWork += new DoWorkEventHandler(bw_DoWork);
        bw.ProgressChanged += new ProgressChangedEventHandler(bw_ProgressChanged);
        bw.WorkerReportsProgress = true;
        bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
        bw.RunWorkerAsync();

    }

    void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        MessageBox.Show("DONE");

    }

    void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        label1.Content = "going here: "+e.ProgressPercentage;
        Debug.WriteLine(e.ProgressPercentage);
    }

    void bw_DoWork(object sender, DoWorkEventArgs e)
    {
        for (int i=0; i < 10000; i++)
        {
            bw.ReportProgress((i*100)/10000);
        }
    }

}

推荐答案

ProgressChanged事件在UI线程而非工作线程上引发.在您的代码中，工作线程几乎什么也没做(只是从0到10000循环并调用ReportProgress)，大部分工作是在UI线程上完成的.基本上，您发送的进度通知太多了.因此，UI线程几乎总是很忙，没有时间呈现标签的新内容.

The ProgressChanged event is raised on the UI thread, not the worker thread. In your code, the worker thread is doing almost nothing (just loop from 0 to 10000 and call ReportProgress), most of the work is done on the UI thread. Basically, you're sending too many progress notifications. Because of this, the UI thread is almost always busy and has no time to render the new content of the label.

当您更改控件的属性时，不会立即执行WPF中的呈现，而是在单独的调度程序框架上完成渲染，当调度程序根据任务的优先级没有其他紧迫的工作时，将对其进行处理.用于渲染的优先级的值为7(DispatcherPriority.Render)； ProgressChanged事件以优先级9(DispatcherPriority.Normal)，

Rendering in WPF is not performed immediately when you change a property of a control, it is done on a separate dispatcher frame, which is processed when the dispatcher has nothing more urgent to do, based on the priority of the task. The priority used for rendering has a value of 7 (DispatcherPriority.Render); the ProgressChanged event is marshalled to the UI thread with a priority of 9 (DispatcherPriority.Normal), as specified on MSDN. So the ProgressChanged notifications always have a higher priority than rendering, and since they keep coming, the dispatcher never has time to process the rendering tasks.

如果您只是降低通知的频率，则您的应用程序应该可以正常运行(当前，您为每个百分比值发送100条通知，这是没有用的):

If you just decrease the frequency of the notifications, your app should work fine (currently you're sending 100 notifications for each percentage value, which is useless):

    void bw_DoWork(object sender, DoWorkEventArgs e)
    {
        for (int i = 0; i < 10000; i++)
        {
            if (i % 100 == 0)
                bw.ReportProgress(i / 100);
        }
    }

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