Silverlight應用程序中的無效跨線程訪問

Question

我正在使用Hammock框架將異步服務從Silverlight應用程序調用到Rest服務。在'完成'回調中，我正在更新綁定到視圖上的組合框的ObservableCollection。

在'OnPropertyChanged'事件處理程序中引發'無效的跨線程訪問'異常。

這是因爲Hammock沒有在UI線程上執行回調？如果不是，爲什麼不呢？這似乎是框架應該處理的功能。我錯過了什麼嗎？我確定不想在每個完成的處理程序中處理自己調用的UI線程。

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); 
} 

感謝

Answer 1

對於綁定屬性和屬性的集合（在觀察集合不是孩子）這是隻需要在UI線程上OnPropertyChanged。屬性可以更早更改，但在調用OnPropertyChanged之前，UI不會更改綁定。

我們所有的ViewModel派生自我們創建的ViewModelBase，它實現了像下面這樣的幫助器SendPropertyChanged（所以我們不必擔心跨線程）。

我們所有的通知屬性調用，而不是直接調用OnPropertyChanged。

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); 
    } 
} 

如果你不使用MVVM，一）道歉和b）不要臉:)：

它也暴露了一個普遍有用OnUiThread方法，這樣你就可以在UI線程上執行任意代碼

Answer 2

吊牀運行在後臺線程你的要求，你絕對要運行它，並處理切換回UI線程自己。否則，您會阻止UI線程，並且您的應用程序將顯示無響應。

要切換回UI界面，您需要Dispatcher上的句柄。得到它最簡單的方法是，像這樣

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

Answer 3

我不喜歡下面

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) 
     { 
     } 
    } 


    } 

}