如何在后台线程中更新显示的时间？

在后台线程中更新显示的时间，通常我们会使用`BackgroundWorker`类或者`Task`和`async`关键字配合。这里以`BackgroundWorker`为例，因为它的设计是为了处理长时间运行的操作而不会阻塞用户界面：

using System;
using System.ComponentModel;
using System.Threading.Tasks;
using System.Windows.Forms;

public partial class MainForm : Form
{
    private BackgroundWorker backgroundWorker = new BackgroundWorker();
    private bool isRunning = false;
    private string executionTimeText = "等待中";

    public MainForm()
    {
        InitializeComponent();
        backgroundWorker.DoWork += Worker_DoWork;
        backgroundWorker.RunWorkerCompleted += Worker_RunWorkerCompleted;
    }

    private void buttonStart_Click(object sender, EventArgs e)
    {
        if (!isRunning)
        {
            isRunning = true;
            backgroundWorker.RunWorkerAsync();
            buttonStart.Enabled = false;
            buttonStop.Enabled = true;
        }
    }

    private void buttonStop_Click(object sender, EventArgs e)
    {
        isRunning = false;
    }

    private void Worker_DoWork(object sender, DoWorkEventArgs e)
    {
        stopwatch.Start();
        while (isRunning && stopwatch.IsRunning)
        {
            // 在这个循环里做你的长时间任务...
            Thread.Sleep(100); // 示例：每100毫秒检查一次

            // 更新执行时间
            if (InvokeRequired)
            {
                Invoke(new Action(() =>
                {
                    executionTimeText = $"执行时间: {stopwatch.Elapsed.TotalSeconds}秒";
                    labelExecutionTime.Text = executionTimeText;
                }));
            }
        }
        stopwatch.Stop();
    }

    private void Worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        isRunning = false;
        buttonStart.Enabled = true;
        buttonStop.Enabled = false;
    }
}

这里，我们在`DoWork`事件中执行长时间任务并在适当的时候调用`Invoke`方法将结果显示到UI线程。当任务完成后，`RunWorkerCompleted`事件会被触发。