"BindingExpression路径错误"；使用ItemsControl和VirtualizingStackPanel [英] "BindingExpression path error" using ItemsControl and VirtualizingStackPanel
问题描述
我在Windows Phone 7上使用Silverlight.
I'm using Silverlight on Windows Phone 7.
使用VirtualizingStackPanel时获得"BindingExpression path error"调试消息是否正常?我认为这是因为视觉项目在回收之后暂时与数据项集合解除了绑定.
Is it normal to get loads of "BindingExpression path error" debug messages when using a VirtualizingStackPanel? I think it is happening because the visual items are temporarily unbound from the data items collection as they are recycled ...
我有一个ItemsControl，其ItemsPanel的ItemsPanelTemplate是VirtualizingStackPanel.它绑定到我的ViewModel上的"Notes" ObservableCollection.
I have an ItemsControl whose ItemsPanel's ItemsPanelTemplate is a VirtualizingStackPanel. It binds to a "Notes" ObservableCollection on my ViewModel.
<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>
这位于UserControl中，该用户控件的DataContext设置为MainViewModel ViewModel.
This is within a UserControl whose DataContext is set to a MainViewModel ViewModel.
ListDataTemplate包含一个Button，按钮本身包含一些文本，这些文本数据绑定到Notes ObservableCollection中的项目的属性:
The ListDataTemplate contains a Button, which itself contains some text, data-bound to a property of the items in the Notes ObservableCollection:
<DataTemplate x:Key="ListDataTemplate">
<Button>
<Grid>
<TextBlock TextWrapping="Wrap" Text="{Binding Title}">
</Grid>
</Button>
</DataTemplate>
当我运行程序时，所有程序都可以正常工作-随时只能绑定到我的Notes集合中的一小部分项目.但是，当我上下滚动时，会遇到很多调试错误:
When I run my program it all works fine - only a small number of items in my Notes collection are bound to at any one time. However I get lots of debug errors as I scroll up and down:
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属性为ItemsSource)-我认为这是正常现象-这是暂时情况，因为可视项未绑定从Notes集合中的项目中删除，以便通过将它们分配给集合中的另一个项目进行回收.
It is looking for the "Title" property on the main view model (whose Notes property is the ItemsSource) - I think this is normal - it is a transient situation as the visual items are unbound from items in the Notes collection in order to be recycled by assigning them to another item in the collection.
还有其他人看到过吗?我对吗，这正常吗?
Has anyone else seen this? Am I right that it is normal?
如果我在MainViewModel上创建了一个虚拟的Title属性并设置了调试断点，那么我会看到此堆栈跟踪.请注意"UnlinkContainerFromItem":
If I create a dummy Title property on my MainViewModel and set a debug breakpoint then I see this stack trace. Note the "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
Thanks, Damian
推荐答案
我认为您对情况的评估是正确的，但这听起来像是VirtualizingStackPanel工作方式中的错误.它不会在需要的地方影响应用程序的执行或绑定，但是引发异常是一项相对昂贵的操作，因此在取消容器链接时相应地更新相应的DataContext是有意义的.
I think your assessment of the situation is correct, but it sounds like a bug in the way the VirtualizingStackPanel works. It's not affecting the execution or bindings of your application at the points where you need it, but raising exceptions is a relatively expensive operation and so it would make sense to update the appropriate DataContext accordingly when unlinking the containers.
我认为将其作为潜在错误的最佳位置是在 App Hub论坛上
I think the best place to raise it as a potential bug would be on the App Hub forums
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