silverlight - "BindingExpression path error"使用 ItemsControl 和 VirtualizingStackPanel

标签 silverlight windows-phone-7 itemscontrol virtualizingstackpanel

我在 Windows Phone 7 上使用 Silverlight。

使用 VirtualizingStackPanel 时收到大量“BindingExpression 路径错误”调试消息是否正常？我认为发生这种情况是因为视觉项在回收时暂时与数据项集合解除绑定(bind)......

我有一个 ItemsControl，其 ItemsPanel 的 ItemsPanelTemplate 是 VirtualizingStackPanel。它绑定(bind)到我的 ViewModel 上的“Notes”ObservableCollection。

<ItemsControl x:Name="ListView" ItemsSource="{Binding Notes}" 
              ItemTemplate="{StaticResource ListDataTemplate}">
    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <VirtualizingStackPanel/>
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>
    <ItemsControl.Template>
        <ControlTemplate>
            <ScrollViewer x:Name="ScrollViewer" Padding="{TemplateBinding Padding}">
                <ItemsPresenter/>
            </ScrollViewer>
        </ControlTemplate>
    </ItemsControl.Template>
</ItemsControl>

这是在 UserControl 中，其 DataContext 设置为 MainViewModel ViewModel。

ListDataTemplate 包含一个 Button，它本身包含一些文本，数据绑定(bind)到 Notes ObservableCollection 中项目的属性:

<DataTemplate x:Key="ListDataTemplate">
        <Button>
        <Grid>
            <TextBlock TextWrapping="Wrap" Text="{Binding Title}">
        </Grid>
    </Button>
</DataTemplate>

当我运行我的程序时，一切正常 - 任何时候只有我的 Notes 集合中的一小部分项目被绑定(bind)。但是，当我上下滚动时，我收到很多调试错误:

System.Windows.Data Error: BindingExpression path error: 'Title' property not found on 'EnWp7.ViewModels.MainViewModel' 'EnWp7.ViewModels.MainViewModel' (HashCode=119211466). BindingExpression: Path='Title' DataItem='EnWp7.ViewModels.MainViewModel' (HashCode=119211466); target element is 'System.Windows.Controls.TextBlock' (Name=''); target property is 'Text' (type 'System.String')..
System.Windows.Data Error: BindingExpression path error: 'Title' property not found on 'EnWp7.ViewModels.MainViewModel' 'EnWp7.ViewModels.MainViewModel' (HashCode=119211466). BindingExpression: Path='Title' DataItem='EnWp7.ViewModels.MainViewModel' (HashCode=119211466); target element is 'System.Windows.Controls.TextBlock' (Name=''); target property is 'Text' (type 'System.String')..
System.Windows.Data Error: BindingExpression path error: 'Title' property not found on 'EnWp7.ViewModels.MainViewModel' 'EnWp7.ViewModels.MainViewModel' (HashCode=119211466). BindingExpression: Path='Title' DataItem='EnWp7.ViewModels.MainViewModel' (HashCode=119211466); target element is 'System.Windows.Controls.TextBlock' (Name=''); target property is 'Text' (type 'System.String')..
System.Windows.Data Error: BindingExpression path error: 'Title' property not found on 'EnWp7.ViewModels.MainViewModel' 'EnWp7.ViewModels.MainViewModel' (HashCode=119211466). BindingExpression: Path='Title' DataItem='EnWp7.ViewModels.MainViewModel' (HashCode=119211466); target element is 'System.Windows.Controls.TextBlock' (Name=''); target property is 'Text' (type 'System.String')..

它正在主视图模型上查找“Title”属性(其 Notes 属性是 ItemsSource) - 我认为这是正常的 - 这是一种短暂的情况，因为视觉项未绑定(bind)来自 Notes 集合中的项目，以便通过将它们分配给集合中的另一个项目来回收。

还有人看过这个吗？我说的对吗？这是正常的吗？

如果我在 MainViewModel 上创建一个虚拟 Title 属性并设置调试断点，那么我会看到此堆栈跟踪。请注意“UnlinkContainerFromItem”:

...!EnWp7.ViewModels.MainViewModel.Title.get() Line 54  C#
mscorlib.dll!System.Reflection.RuntimeMethodInfo.InternalInvoke(System.Reflection.RuntimeMethodInfo rtmi = {System.Reflection.RuntimeMethodInfo}, object obj = {EnWp7.ViewModels.MainViewModel}, System.Reflection.BindingFlags invokeAttr = Default, System.Reflection.Binder binder = null, object parameters = null, System.Globalization.CultureInfo culture = null, bool isBinderDefault = false, System.Reflection.Assembly caller = null, bool verifyAccess = true, ref System.Threading.StackCrawlMark stackMark = LookForMyCaller) 
mscorlib.dll!System.Reflection.RuntimeMethodInfo.InternalInvoke(object obj = {EnWp7.ViewModels.MainViewModel}, System.Reflection.BindingFlags invokeAttr = Default, System.Reflection.Binder binder = null, object[] parameters = null, System.Globalization.CultureInfo culture = null, ref System.Threading.StackCrawlMark stackMark = LookForMyCaller) + 0x14e bytes 
mscorlib.dll!System.Reflection.RuntimePropertyInfo.InternalGetValue(System.Reflection.PropertyInfo thisProperty = {System.Reflection.RuntimePropertyInfo}, object obj = {EnWp7.ViewModels.MainViewModel}, object[] index = null, ref System.Threading.StackCrawlMark stackMark = LookForMyCaller) + 0x4e bytes  
mscorlib.dll!System.Reflection.RuntimePropertyInfo.GetValue(object obj = {EnWp7.ViewModels.MainViewModel}, object[] index = null) + 0x2 bytes   
System.Windows.dll!System.Windows.CLRPropertyListener.Value.get() + 0x1b bytes  
System.Windows.dll!System.Windows.PropertyAccessPathStep.ConnectToPropertyInSource() + 0x148 bytes  
System.Windows.dll!System.Windows.PropertyAccessPathStep.ConnectToProperty() + 0x16 bytes   
System.Windows.dll!System.Windows.PropertyAccessPathStep.ReConnect(object newSource = {EnWp7.ViewModels.MainViewModel}) + 0x13 bytes    
System.Windows.dll!System.Windows.PropertyPathListener.ReConnect(object source = {EnWp7.ViewModels.MainViewModel}) + 0x10 bytes 
System.Windows.dll!System.Windows.Data.BindingExpression.SourceAquired() + 0x11 bytes   
System.Windows.dll!System.Windows.Data.BindingExpression.DataContextChanged(object o = {System.Windows.Controls.TextBlock}, System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x26 bytes   
System.Windows.dll!System.Windows.FrameworkElement.OnDataContextChanged(System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x15 bytes   
System.Windows.dll!System.Windows.FrameworkElement.OnAncestorDataContextChanged(System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x11 bytes   
System.Windows.dll!System.Windows.FrameworkElement.NotifyDataContextChanged(System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x59 bytes   
System.Windows.dll!System.Windows.FrameworkElement.OnAncestorDataContextChanged(System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x18 bytes   
System.Windows.dll!System.Windows.FrameworkElement.NotifyDataContextChanged(System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x59 bytes   
System.Windows.dll!System.Windows.FrameworkElement.OnAncestorDataContextChanged(System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x18 bytes   
System.Windows.dll!System.Windows.FrameworkElement.NotifyDataContextChanged(System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x59 bytes   
System.Windows.dll!System.Windows.FrameworkElement.OnAncestorDataContextChanged(System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x18 bytes   
System.Windows.dll!System.Windows.FrameworkElement.NotifyDataContextChanged(System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x59 bytes   
System.Windows.dll!System.Windows.FrameworkElement.OnAncestorDataContextChanged(System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x18 bytes   
System.Windows.dll!System.Windows.FrameworkElement.NotifyDataContextChanged(System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x59 bytes   
System.Windows.dll!System.Windows.FrameworkElement.OnAncestorDataContextChanged(System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x18 bytes   
System.Windows.dll!System.Windows.FrameworkElement.NotifyDataContextChanged(System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x59 bytes   
System.Windows.dll!System.Windows.FrameworkElement.OnAncestorDataContextChanged(System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x18 bytes   
System.Windows.dll!System.Windows.FrameworkElement.NotifyDataContextChanged(System.Windows.DataContextChangedEventArgs e = {System.Windows.DataContextChangedEventArgs}) + 0x59 bytes   
System.Windows.dll!System.Windows.FrameworkElement.OnPropertyChanged(System.Windows.DependencyProperty dp = {System.Windows.CoreDependencyProperty}) + 0x1d bytes   
System.Windows.dll!System.Windows.DependencyObject.RaisePropertyChangeNotifications(System.Windows.DependencyProperty dp = {System.Windows.CoreDependencyProperty}, object newValue = {EnWp7.ViewModels.MainViewModel}, object oldValue = {EnWp7.Store.NoteLocal}) + 0x38 bytes 
System.Windows.dll!System.Windows.DependencyObject.ClearValueInternal(System.Windows.DependencyProperty dp = {System.Windows.CoreDependencyProperty}) + 0x138 bytes 
System.Windows.dll!System.Windows.DependencyObject.ClearValue(System.Windows.DependencyProperty dp = {System.Windows.CoreDependencyProperty}) + 0x7 bytes   
System.Windows.dll!System.Windows.Controls.ItemContainerGenerator.UnlinkContainerFromItem(System.Windows.DependencyObject container = {System.Windows.Controls.ContentPresenter}, object item = {EnWp7.Store.NoteLocal}, bool isRecycling = true) + 0x1f bytes  
System.Windows.dll!System.Windows.Controls.ItemContainerGenerator.Remove(System.Windows.Controls.Primitives.GeneratorPosition position = {System.Windows.Controls.Primitives.GeneratorPosition}, int count = 2, bool isRecycling = true) + 0x14a bytes  
System.Windows.dll!System.Windows.Controls.ItemContainerGenerator.System.Windows.Controls.Primitives.IRecyclingItemContainerGenerator.Recycle(System.Windows.Controls.Primitives.GeneratorPosition position = {System.Windows.Controls.Primitives.GeneratorPosition}, int count = 2) + 0x9 bytes    
System.Windows.dll!System.Windows.Controls.VirtualizingStackPanel.CleanupRange(int startIndex = 0, int count = 2) + 0x20 bytes  
System.Windows.dll!System.Windows.Controls.VirtualizingStackPanel.CleanupContainers(System.Windows.Controls.ItemsControl itemsControl = {System.Windows.Controls.ItemsControl}) + 0x73 bytes    
System.Windows.dll!System.Windows.Controls.VirtualizingStackPanel.MeasureOverride(System.Windows.Size constraint = {System.Windows.Size}) + 0xe4 bytes  
System.Windows.dll!System.Windows.FrameworkElement.MeasureOverride(System.IntPtr nativeTarget = 102509504, float inWidth = 480.0, float inHeight = 499.0, out float outWidth = 0.0, out float outHeight = 0.0) + 0x45 bytes

谢谢， 达米安

最佳答案

我认为您对情况的评估是正确的，但这听起来像是VirtualizingStackPanel工作方式中的一个错误。它不会影响应用程序在需要时的执行或绑定(bind)，但引发异常是一项相对昂贵的操作，因此在取消链接容器时相应地更新适当的 DataContext 是有意义的。

我认为将其作为潜在错误提出的最佳位置是 App Hub forums

关于silverlight - "BindingExpression path error"使用 ItemsControl 和 VirtualizingStackPanel，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/4950208/

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