Question

我正在使用Hammock框架从Silverlight应用程序到Rest服务进行异步服务调用。在'完成'回调中，我正在更新一个ObservableCollection，它绑定到视图上的组合框。

“OnPropertyChanged”事件处理程序中抛出了“无效的跨线程访问”异常。

这是因为Hammock没有在UI线程上执行回调吗？如果没有，为什么不呢？这似乎是框架应该处理的功能。我错过了什么吗？我确定不想在每个完成的处理程序中自己处理UI线程的调用。

public void LoadMyData()
{
    var request = new RestRequest();
    request.Path = "MyRestUrlText";

    var callback = new RestCallback(
      (restRequest, restResponse, userState) =>
      {
        var visibleData = new ObservableCollection<MyDataType>();

        var myData = JsonConvert.DeserializeObject<MyDataType[]> restResponse.Content);

        foreach (var item in myData)
            visibleData .Add(item);

        this.MyBoundCollection = visibleData;
        OnPropertyChanged("MyBoundCollection");
    });

    var asyncResult = _restClient.BeginRequest(request, callback);
}

由于

Answer 1

对于作为集合的绑定属性和属性（而不是可观察集合中的子节点），只有OnPropertyChanged需要位于UI线程上。属性可以更早更改，但在调用OnPropertyChanged之前，UI不会更改绑定。

我们所有的ViewModel派生自我们创建的ViewModelBase，它实现了如下所示的助手SendPropertyChanged（所以我们永远不必担心跨线程）。

我们所有的通知属性都会调用它而不是直接调用OnPropertyChanged。

它还公开了一个通常有用的OnUiThread方法，因此您可以在UI线程上执行任意代码：

protected delegate void OnUiThreadDelegate();

public event PropertyChangedEventHandler PropertyChanged;

public void SendPropertyChanged(string propertyName)
{
    if (this.PropertyChanged != null)
    {
        this.OnUiThread(() => this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName)));
    }
}

protected void OnUiThread(OnUiThreadDelegate onUiThreadDelegate)
{
    if (Deployment.Current.Dispatcher.CheckAccess())
    {
        onUiThreadDelegate();
    }
    else
    {
        Deployment.Current.Dispatcher.BeginInvoke(onUiThreadDelegate);
    }
}

如果你没有使用MVVM，a）道歉并且b）羞辱你：）

Answer 2

Hammock正在后台线程上运行您的请求，您绝对想在那里运行它并自己切换回UI线程。否则，您将阻止UI线程，您的应用程序将显示无响应。

要切换回用户界面，您需要在Dispatcher上设置一个句柄。获得它的最简单方法就是这样

Deployment.Current.Dispatcher.BeginInvoke(() => {
    this.MyBoundCollection = visibleData;
    OnPropertyChanged("MyBoundCollection");
});

Answer 3

我确实喜欢下面

namespace IdleStateDetection
{

  public partial class App : Application
  {

    private bool idle = true;

    private System.Threading.Timer _sessionTimeOutTimer = null;

    public App()
    {
      this.Startup += this.Application_Startup;
      this.Exit += this.Application_Exit;
      this.UnhandledException += this.Application_UnhandledException;

      Application.Current.RootVisual.MouseMove += new MouseEventHandler(RootVisual_MouseMove);
      Application.Current.RootVisual.KeyDown += new KeyEventHandler(RootVisual_KeyDown);

      _sessionTimeOutTimer = new Timer(SessionTimeOutCheck, null, 20000, 60000);
      InitializeComponent();
    }

    private void Application_Startup(object sender, StartupEventArgs e)
    {

      this.RootVisual = new MainPage();
    }


    void RootVisual_KeyDown(object sender, KeyEventArgs e)
    {
      idle = false;

    }

    void RootVisual_MouseMove(object sender, MouseEventArgs e)
    {
      idle = false;

    }

    private void SessionTimeOutCheck(object state)
    {
      if (Deployment.Current.Dispatcher.CheckAccess())
      {
        ShowMessage();
      }
      else
      {
        Deployment.Current.Dispatcher.BeginInvoke(()=>{ShowMessage();});
      }

    }

    private void ShowMessage()
    {
      if (idle == true)
      {
        MessageBox.Show("Idle");
      }
    }

    private void Application_Exit(object sender, EventArgs e)
    {

    }

    private void Application_UnhandledException(object sender, ApplicationUnhandledExceptionEventArgs e)
    {
      // If the app is running outside of the debugger then report the exception using
      // the browser's exception mechanism. On IE this will display it a yellow alert 
      // icon in the status bar and Firefox will display a script error.
      if (!System.Diagnostics.Debugger.IsAttached)
      {

        // NOTE: This will allow the application to continue running after an exception has been thrown
        // but not handled. 
        // For production applications this error handling should be replaced with something that will 
        // report the error to the website and stop the application.
        e.Handled = true;
        Deployment.Current.Dispatcher.BeginInvoke(delegate { ReportErrorToDOM(e); });
      }
    }

    private void ReportErrorToDOM(ApplicationUnhandledExceptionEventArgs e)
    {
      try
      {
        string errorMsg = e.ExceptionObject.Message + e.ExceptionObject.StackTrace;
        errorMsg = errorMsg.Replace('"', '\'').Replace("\r\n", @"\n");

        System.Windows.Browser.HtmlPage.Window.Eval("throw new Error(\"Unhandled Error in Silverlight Application " + errorMsg + "\");");
      }
      catch (Exception)
      {
      }
    }


  }

}

Silverlight应用程序中的跨线程访问无效

3 个答案: