从另一个线程更新标签的最简单方法是什么?

我在thread1上运行了一个Form,然后我开始另一个线程(thread2)。当thread2处理一些文件时,我想用thread2工作的当前状态更新表单上的标签。

我怎么能这样做?


当前回答

您可以使用现有的委托操作:

private void UpdateMethod()
{
    if (InvokeRequired)
    {
        Invoke(new Action(UpdateMethod));
    }
}

其他回答

将一些公共变量放在一个单独的类中以保存值。

例子:

public  class data_holder_for_controls
{
    // It will hold the value for your label
    public string status = string.Empty;
}

class Demo
{
    public static  data_holder_for_controls d1 = new data_holder_for_controls();

    static void Main(string[] args)
    {
        ThreadStart ts = new ThreadStart(perform_logic);
        Thread t1 = new Thread(ts);
        t1.Start();
        t1.Join();
        //your_label.Text=d1.status; --- can access it from any thread
    }

    public static void perform_logic()
    {
        // Put some code here in this function
        for (int i = 0; i < 10; i++)
        {
            // Statements here
        }
        // Set the result in the status variable
        d1.status = "Task done";
    }
}

WPF应用程序中最简单的方法是:

this.Dispatcher.Invoke((Action)(() =>
{
    // This refers to a form in a WPF application 
    val1 = textBox.Text; // Access the UI 
}));

我无法理解这一丑陋实现背后的微软逻辑,但你必须有两个功能:

void setEnableLoginButton()
{
  if (InvokeRequired)
  {
    // btn_login can be any conroller, (label, button textbox ..etc.)

    btn_login.Invoke(new MethodInvoker(setEnable));

    // OR
    //Invoke(new MethodInvoker(setEnable));
  }
  else {
    setEnable();
  }
}

void setEnable()
{
  btn_login.Enabled = isLoginBtnEnabled;
}

这些片段对我有用,所以我可以在另一个线程上执行一些操作,然后更新GUI:

Task.Factory.StartNew(()=>
{
    // THIS IS NOT GUI
    Thread.Sleep(5000);
    // HERE IS INVOKING GUI
    btn_login.Invoke(new Action(() => DoSomethingOnGUI()));
});

private void DoSomethingOnGUI()
{
   // GUI
   MessageBox.Show("message", "title", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
}

更简单的是:

btn_login.Invoke(new Action(()=>{ /* HERE YOU ARE ON GUI */ }));

这是一个古老问题的新视角,使用了更实用的风格。如果您在所有项目中都保留TaskXM类,那么只有一行代码不再担心跨线程更新。

public class Example
{
    /// <summary>
    /// No more delegates, background workers, etc. Just one line of code as shown below.
    /// Note it is dependent on the Task Extension method shown next.
    /// </summary>
    public async void Method1()
    {
        // Still on the GUI thread here if the method was called from the GUI thread
        // This code below calls the extension method which spins up a new task and calls back.
        await TaskXM.RunCodeAsync(() =>
        {
            // Running an asynchronous task here
            // Cannot update the GUI thread here, but can do lots of work
        });
        // Can update GUI on this line
    }
}


/// <summary>
/// A class containing extension methods for the Task class
/// </summary>
public static class TaskXM
{
    /// <summary>
    /// RunCodeAsyc is an extension method that encapsulates the Task.run using a callback
    /// </summary>
    /// <param name="Code">The caller is called back on the new Task (on a different thread)</param>
    /// <returns></returns>
    public async static Task RunCodeAsync(Action Code)
    {
        await Task.Run(() =>
        {
            Code();
        });
        return;
    }
}

线程代码经常有bug,而且总是很难测试。您不需要编写线程代码来从后台任务更新用户界面。只需使用BackgroundWorker类来运行任务及其ReportProgress方法来更新用户界面。通常,您只报告完成百分比,但还有一个重载包含状态对象。下面是一个仅报告字符串对象的示例:

    private void button1_Click(object sender, EventArgs e)
    {
        backgroundWorker1.WorkerReportsProgress = true;
        backgroundWorker1.RunWorkerAsync();
    }

    private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
    {
        Thread.Sleep(5000);
        backgroundWorker1.ReportProgress(0, "A");
        Thread.Sleep(5000);
        backgroundWorker1.ReportProgress(0, "B");
        Thread.Sleep(5000);
        backgroundWorker1.ReportProgress(0, "C");
    }

    private void backgroundWorker1_ProgressChanged(
        object sender, 
        ProgressChangedEventArgs e)
    {
        label1.Text = e.UserState.ToString();
    }

如果您总是想更新同一个字段,这很好。如果要进行更复杂的更新,可以定义一个类来表示UI状态,并将其传递给ReportProgress方法。

最后一件事,确保设置WorkerReportsProgress标志,否则ReportProgress方法将被完全忽略。