如何在xaml中顯示調度程序數據（MVVM + WP8）

Question

我想在手機屏幕上查看我當前的位置。我在這個項目中使用MVVM模型。

XAML

<TextBlock Name="XBlock" 
           Visibility="Visible" 
           Text="{Binding Path=XValue, Mode=OneWay}" 
           Margin="0,0,359,0" Height="75"/> 

視圖模型

public string XValue {get ; set ; } 
     public string YValue { get; set; } 
     public string ZValue { get; set; } 

     void _accelerometer_CurrentValueChanged(object sender, SensorReadingEventArgs<AccelerometerReading> e) 
     { 
      var position = e.SensorReading.Acceleration; 

      SmartDispatcher.Dispatch(() => 
      { 
       this.XValue = position.X.ToString("0.0000"); 
       this.YValue = position.Y.ToString("0.0000"); 
       this.ZValue = position.Z.ToString("0.0000"); 
      }); 
     } 

分派器類

public static Dispatcher DispatchObject { get; set; } 

     public static void Dispatch(Action action) 
     { 
      if (DispatchObject == null || DispatchObject.CheckAccess()) 
      { 
       action(); 
      } 
      else 
      { 
       DispatchObject.InvokeAsync(action); 
      } 
     } 

TextBlock中是空的。來自加速計的數據被正確讀取（由Degug檢查）。

當我將改變方法x值到：

public string XValue { 
      get { return "ds"; } 
      set{ XValue = "fd";} 
     } 

在TextBlock的是： 「DS」。 如何查看當前的加速度計數據？

Answer 1

您必須將INotifyPropertyChanged接口添加到ViewModel，以便Xaml知道數據何時更改並可以更新。

例子：

public class MyViewModel : INotifyPropertyChanged 
{ 
    private string _zValue; 
    private string _yValue; 
    private string _xValue; 

    public string XValue 
    { 
     get { return _xValue; } 
     set { _xValue = value; NotifyPropertyChanged("XValue"); } 
    } 

    public string YValue 
    { 
     get { return _yValue; } 
     set { _yValue = value; NotifyPropertyChanged("YValue"); } 

    } 
    public string ZValue 
    { 
     get { return _zValue; } 
     set { _zValue = value; NotifyPropertyChanged("ZValue"); } 
    } 

    void _accelerometer_CurrentValueChanged(object sender, SensorReadingEventArgs<AccelerometerReading> e) 
    { 
     var position = e.SensorReading.Acceleration; 

     SmartDispatcher.Dispatch(() => 
     { 
      this.XValue = position.X.ToString("0.0000"); 
      this.YValue = position.Y.ToString("0.0000"); 
      this.ZValue = position.Z.ToString("0.0000"); 
     }); 
    } 


    public event PropertyChangedEventHandler PropertyChanged; 
    private void NotifyPropertyChanged(string propertyName) 
    { 
     if (PropertyChanged != null) 
     { 
      PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); 
     } 
    } 
} 

Answer 2

不起作用。 Erron在：

PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); 

詳情：

System.UnauthorizedAccessException was unhandled by user code 
    HResult=-2147024891 
    Message=Invalid cross-thread access. 
    Source=System.Windows 
    StackTrace: 
     at MS.Internal.XcpImports.CheckThread() 
     at MS.Internal.XcpImports.GetValue(IManagedPeerBase managedPeer, DependencyProperty property) 
     at System.Windows.DependencyObject.GetOldValue(DependencyProperty property, EffectiveValueEntry& oldEntry) 
     at System.Windows.DependencyObject.UpdateEffectiveValue(DependencyProperty property, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, ValueOperation operation) 
     at System.Windows.DependencyObject.RefreshExpression(DependencyProperty dp) 
     at System.Windows.Data.BindingExpression.SendDataToTarget() 
     at System.Windows.Data.BindingExpression.SourcePropertyChanged(PropertyPathListener sender, PropertyPathChangedEventArgs args) 
     at System.Windows.PropertyPathListener.RaisePropertyPathStepChanged(PropertyPathStep source) 
     at System.Windows.PropertyAccessPathStep.RaisePropertyPathStepChanged(PropertyListener source) 
     at System.Windows.CLRPropertyListener.SourcePropertyChanged(Object sender, PropertyChangedEventArgs args) 
     at System.Windows.Data.WeakPropertyChangedListener.PropertyChangedCallback(Object sender, PropertyChangedEventArgs args) 
     at System.ComponentModel.PropertyChangedEventHandler.Invoke(Object sender, PropertyChangedEventArgs e) 
     at ITWEMPhone.ViewModel.NotifyPropertyChanged(String propertyName) 
     at ITWEMPhone.ViewModel.set_XValue(String value) 
     at ITWEMPhone.ViewModel.<>c__DisplayClass1.<_accelerometer_CurrentValueChanged>b__0() 
     at ITWEMPhone.SmartDispatcher.Dispatch(Action action) 
     at ITWEMPhone.ViewModel._accelerometer_CurrentValueChanged(Object sender, SensorReadingEventArgs`1 e) 
     at System.EventHandler`1.Invoke(Object sender, TEventArgs e) 
     at Microsoft.Devices.Sensors.SensorBase`1.FireOnReadingChanged(SensorReadingEventArgs`1 sample) 
     at Microsoft.Devices.Sensors.SensorBase`1.OnNewReading(Object sender, NativeSensorEventArgs sample) 
     at Microsoft.Devices.Sensors.SensorBase`1.<>c__DisplayClass7.<.ctor>b__3(Object sender, NativeSensorEventArgs args) 
     at Microsoft.Devices.Sensors.SensorCallback.OnNewReading(IntPtr pNewReading) 
    InnerException: 

因此，我改變方法：

private void NotifyPropertyChanged(string propertyName) 
     { 
      Deployment.Current.Dispatcher.BeginInvoke(() => PropertyChanged(this, new PropertyChangedEventArgs(propertyName))); 
     } 

和XAML到：

<TextBlock Text="{Binding XValue, Mode=TwoWay}" Height="67" RenderTransformOrigin="0.5,1.134"/> 

和工程完美:)瑪米說將會對某人有用！