执行期间WPF标签内容显示

对不起，对于WPF，我是个新手：

当我单击一个按钮时，我希望在函数启动时看到标签中显示的一条消息，然后我希望在函数完成时看到另一条消息

在这里的代码中，我只看到单击按钮时显示的最后一条消息值。有人能给我解释一下原因吗

既然这不起作用，我该如何实现我真正想要的——在一段时间内看到一条消息（如“处理”），然后在函数完成时看到另一条消息（如“完成”）

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        MessageLabel.Content = "I never see this";

        System.Threading.Thread.Sleep(2000);

        MessageLabel.Content = "I only see this";
    }
}

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谢谢你，布拉希玛！下面是我希望对BackgroundWorker对象执行的代码

public partial class MainWindow : Window
{
    private BackgroundWorker backgroundWorker1 = new BackgroundWorker();

    public MainWindow()
    {
        InitializeComponent();

        backgroundWorker1.WorkerReportsProgress = true;
        backgroundWorker1.WorkerSupportsCancellation = false;

        backgroundWorker1.DoWork += worker_DoWork;
        backgroundWorker1.RunWorkerCompleted += worker_RunWorkerCompleted;
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        MessageLabel.Content = "I see this now";

        if (backgroundWorker1.IsBusy != true)
        {
            backgroundWorker1.RunWorkerAsync(); 
        }
    }

    private void worker_DoWork(object sender, DoWorkEventArgs e)
    {
        System.Threading.Thread.Sleep(2000);
    }

    private void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        MessageLabel.Content = "and I see this too";
    }
}

---

您看不到更改的原因是，这都是在UI线程上运行的，在第二次更新标签之前，UI线程没有机会刷新您的屏幕。
您应该使用来运行代码的“重”部分（例如，标签的Sleep+更新）

代码的快速示例：

private void Button_Click(object sender, RoutedEventArgs e)
{
    MessageLabel.Content = "I never see this";

    BackgroundWorker bw = new BackgroundWorker();
    bw.DoWork += (s,a) =>
          {
                Thread.Sleep(2000);
          };
    bw.RunWorkerCompleted += (s, a) =>
          {
                MessageLabel.Content = "I saw it now";
          };
    bw.RunWorkerAsync(); // Start BackgroundWorker