使用BackgroundWorker

Posted 2020-09-04 sekon

1，WPF应用程序为单线程模型（STAThread)，所有UI控件都是主线程创建的，只有主线程能操作UI元素的显示。

2，其他工作线程要维护UI控件的显示，需调用主线程的Dispather，执行Invoke(同步）或BeginInvoke(异步）方法。

3，UI线程如时行耗时的操作，将使UI假死，用户体验较差。应使用后台线程进行耗时操作，并异步更新UI。

4，BackgroundWorker是WPF的一个后台工作类，代码说明一切：

前台：

    <StackPanel>
        <ProgressBar Name="progressBar" Height="20" Width="200" Margin="10"></ProgressBar>
        <Button Name="btnProcess" Width="100" Click="btnProcess_Click" Margin="5">开始后台任务</Button>
        <Button Name="btnCancel" Width="100" Click="btnCancel_Click" Margin="5">取消后台任务</Button>
    </StackPanel>

后台：

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

            bgWorker.WorkerReportsProgress = true;
            bgWorker.WorkerSupportsCancellation = true;
            bgWorker.DoWork += DoWork_Handler;
            bgWorker.ProgressChanged += ProgressChanged_Handler;
            bgWorker.RunWorkerCompleted += RunWorkerCompleted_Handler;
        }

        private void btnProcess_Click(object sender, RoutedEventArgs e)
        {
            if (!bgWorker.IsBusy)
            {
                bgWorker.RunWorkerAsync();
            }
        }

        private void ProgressChanged_Handler(object sender, ProgressChangedEventArgs args)
        {
               progressBar.Value = args.ProgressPercentage;
           
        }

        //后台线程运行的程序
        private void DoWork_Handler(object sender, DoWorkEventArgs args)
        {
            BackgroundWorker worker = sender as BackgroundWorker;
            for (int i = 1; i <= 100; i++)
            {
                if (worker.CancellationPending)
                {
                    args.Cancel = true;
                    break;
                }
                else
                {
                    worker.ReportProgress(i);

                    //因为这在后台线程，要想直接修改UI控件，需用Invoke或BeginInvoke方法
                    //this.Dispatcher.Invoke(new Action(() =>
                    //{
                    //    progressBar.Value = i;
                    //}));

                    Thread.Sleep(100);  //因为频繁调用UI线程，为了给UI线程反应时间，这里让后台线程稍顿一下
                }
            }

        }

        private void RunWorkerCompleted_Handler(object sender, RunWorkerCompletedEventArgs args)
        {
            progressBar.Value = 0;
            if (args.Cancelled)
            {
                MessageBox.Show("后台任务已经被取消。", "消息");
            }
            else
            {
                MessageBox.Show("后台任务正常结束。", "消息");
            }
        }
        private void btnCancel_Click(object sender, RoutedEventArgs e)
        {
            bgWorker.CancelAsync();
        }
    }