多线程 c# WPF

Question

我在将值从 c# 代码绑定到 WPF UI 时遇到问题。 我已经了解了线程的基础知识，并且知道我必须使用 Dispatcher 来绑定自定义后台线程中的 ui 线程。

我有一个需求，我想通过每秒访问 nse-stockmarket api 并相应地执行一些逻辑来不断更新我的 WPF UI，以便我可以显示天气股价正在上涨或下跌。

下面是我试图实现这一目标的代码......

注意：我没有遇到任何异常，甚至“跨线程”也没有

 //globally declared var stockName = "";
 //wpf button click 
 private void Button_Click(object sender, RoutedEventArgs e)
  {

      stockName = "LUPIN";
      new Thread(() =>
          {
            RunStockParallel(share.Key);
            Action action = new Action(SetTextBoxValues);

          }).Start();

   }    



public void RunStockParallel(string stockName){
  var count = 0 ;
           do
            {
                HttpWebRequest stocks = null;
                try
                {
                    //your logic will be here.. 
                }
                catch (Exception e)
                {
                    //throw e;
                }


      //It will call the delegate method so that UI can update. 
                Action action = new Action(SetTextBoxValues);

                stockName = count++;
            } while (true);
}




 private void SetTextBoxValues()
        {
            this.Dispatcher.Invoke(() =>
            {

                this.text1.Text = stockName;

            });

        }

当我使用 do-while 循环时，它会一直循环，直到我终止应用程序。在这个 do-while 循环中，我不断尝试通过使用“counter++;”更新 Text1 文本框来更新 WPF ui。

但它没有按预期工作。需要建议或解决方案。 :)

Answer 1

您没有调用您正在创建的委托。此外，您要递增的变量不是您用于更新 UI 的变量。您只是升级方法 RunStockParallel() 的局部变量。

以下是工作版本。希望对您有所帮助。

PS：我建议不要在生产中使用下面的代码。当你关闭你的应用程序时，SetTextBoxValues() 会抛出一个TaskCanceledException 这一点都不理想。正如有人已经提到的，这可能是执行并发任务的一种非常老式的方式。您可能希望切换到使用基于Task 或async/await 的方法，您可以通过使用CancellationToken 非常有效地避免此类异常。

private void Button_Click(object sender, RoutedEventArgs e)
  {

     stockName = "LUPIN";
     new Thread(() =>
        {
           RunStockParallel(stockName);
           Action action = new Action(SetTextBoxValues); // Maybe this is not required? But this was present in your original code, so I left it as is.
        }).Start();
  }

  public void RunStockParallel(string stockName)
  {
     var count = 0;
     do
     {
        HttpWebRequest stocks = null;
        try
        {
           //your logic will be here.. 
        }
        catch (Exception e)
        {
           //throw e;
        }

        //It will call the delegate method so that UI can update. 
        Action action = new Action(SetTextBoxValues);
        //Invoke the delegate
        action();
        //Increment the globally declared var stockname
        this.stockName = count++.ToString();

     } while (true);
  }

  private void SetTextBoxValues()
  {
     this.Dispatcher.Invoke(() =>
           {
              this.text1.Text = stockName;
           });
  }

Answer 2

@tushardevsharma

我得到了这个答案。我在 RunStockParallel 方法中的代码的下面添加了 try catch 块中的代码。我的主要逻辑部分与此

HttpWebRequest stocks = null;
try
{
   //your logic will be here.. 

       Dispatcher.BeginInvoke(new Action(() =>
       {
           txtName.Text = stockName;


       }), DispatcherPriority.Background);

}
catch (Exception e)
{
   //throw e;
}

Answer 3

我会用 WPF 的方式来做，所以你不需要关心使用 Dispatcher...

XAML 代码：

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApplication1"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525" d:DataContext="{d:DesignInstance local:ViewModel}">
    <StackPanel>
        <Button Command="{Binding StartPollingCommand}" Content="Start Polling" />
        <TextBlock Text="{Binding StockValue}" />
    </StackPanel>
</Window>

您的 C# 代码：

public partial class MainWindow {
    public MainWindow() {
        InitializeComponent();
        DataContext = new ViewModel();
    }
}

public class ViewModel : INotifyPropertyChanged {
    private string _stockValue;
    public event PropertyChangedEventHandler PropertyChanged;

    public ICommand StartPollingCommand {
        get { return new RelayCommand(param => DoExecuteStartPollingCommand()); }
    }

    private void DoExecuteStartPollingCommand() {
        try {
            Task.Run(() => RunStockParallel("StockName"));
        } catch (Exception ex) {
            //TODO
        }
    }

    private void RunStockParallel(string stockName) {
        var count = 0;
        do {

            try {
                // Do Something to get your Data
                //HttpWebRequest stocks = null;
                var stockresults = DateTime.Now;
                StockValue = stockresults.ToString();
            } catch (Exception e) {
                //throw e;
            }
            //Wait some time before getting the next stockresults
            Thread.Sleep(1000);
        } while (true);
    }

    public string StockValue {
        get => _stockValue;
        set {
            _stockValue = value;
            OnPropertyChanged();
        }
    }

    [NotifyPropertyChangedInvocator]
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null) {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

public class RelayCommand : ICommand {
    #region Fields

    readonly Action<object> _execute;
    readonly Predicate<object> _canExecute;

    #endregion // Fields

    #region Constructors

    /// <summary>
    /// Creates a new command that can always execute.
    /// </summary>
    /// <param name="execute">The execution logic.</param>
    public RelayCommand(Action<object> execute)
        : this(execute, null) { }

    /// <summary>
    /// Creates a new command.
    /// </summary>
    /// <param name="execute">The execution logic.</param>
    /// <param name="canExecute">The execution status logic.</param>
    public RelayCommand(Action<object> execute, Predicate<object> canExecute) {
        if (execute == null)
            throw new ArgumentNullException("execute"); //NOTTOTRANS

        _execute = execute;
        _canExecute = canExecute;
    }

    #endregion // Constructors

    #region ICommand Members

    [DebuggerStepThrough]
    public bool CanExecute(object parameter) {
        return _canExecute == null ? true : _canExecute(parameter);
    }

    public event EventHandler CanExecuteChanged {
        add => CommandManager.RequerySuggested += value;
        remove => CommandManager.RequerySuggested -= value;
    }

    public void Execute(object parameter) {
        _execute(parameter);
    }

    #endregion // ICommand Members
}

您应该在关闭应用程序之前顺利结束正在运行的Task...

Answer 4

我不知道您遇到了什么错误，但假设您遇到了跨线程操作无效错误。可能是因为这条线

this.text1.Text = stockName;

您正在直接访问 text1，因此将向您显示有关跨线程的错误。一种安全的方法是使用委托函数调用 .Text 方法

this.text1.Invoke(new Action(() => this.text1.Text = stockName));

我没有测试过，但你有这个想法。 如果您想进行跨线程安全调用。你可以参考这个

Cross-thread operation not valid: Control 'textBox1' accessed from a thread other than the thread it was created on

Answer 5

您在代码中的问题是没有睡眠。线程太忙了。 您需要在 while 循环中添加 Thread.Sleep(100) 或使用信号量。