ListPicker崩溃

Question

我有一个结构如下的ListPicker：

toolkit:ListPicker x:Name="mListPicker" HorizontalAlignment="Right" Margin="0,75,43,0" Width="100" VerticalAlignment="Top">
< toolkit:ListPickerItem Content="5"/>
< toolkit:ListPickerItem Content="10"/>
< toolkit:ListPickerItem Content="15"/>
< toolkit:ListPickerItem Content="20"/>
< toolkit:ListPickerItem Content="25"/>
< toolkit:ListPickerItem Content="30"/>
< /toolkit:ListPicker>

每当我尝试运行此命令时，都会出现以下消息：

System.Windows.Markup.XamlParseException occurred
  Message= [Line: 0 Position: 0]
   --- Inner Exception ---
The parameter is incorrect. 

  LineNumber=0
  LinePosition=0
  StackTrace:
       at MS.Internal.XcpImports.MethodEx(IntPtr ptr, String name, CValue[] cvData)
       at MS.Internal.XcpImports.MethodEx(DependencyObject obj, String name)
       at MS.Internal.XcpImports.FrameworkElement_ApplyTemplate(FrameworkElement frameworkElement)
       at System.Windows.FrameworkElement.ApplyTemplateInternal()
       at System.Windows.Controls.ScrollContentPresenter.HookupScrollingComponents()
       at System.Windows.Controls.ScrollContentPresenter.OnApplyTemplate()
       at System.Windows.FrameworkElement.OnApplyTemplate(IntPtr nativeTarget)
       at MS.Internal.XcpImports.MeasureNative(IntPtr element, Single inWidth, Single inHeight)
       at MS.Internal.XcpImports.UIElement_Measure(UIElement element, Size availableSize)
       at System.Windows.UIElement.Measure(Size availableSize)
       at System.Windows.Controls.ScrollViewer.MeasureOverride(Size constraint)
       at System.Windows.FrameworkElement.MeasureOverride(IntPtr nativeTarget, Single inWidth, Single inHeight, Single& outWidth, Single& outHeight)
       at MS.Internal.XcpImports.MeasureOverrideNative(IntPtr element, Single inWidth, Single inHeight, Single& outWidth, Single& outHeight)
       at MS.Internal.XcpImports.FrameworkElement_MeasureOverride(FrameworkElement element, Size availableSize)
       at System.Windows.FrameworkElement.MeasureOverride(Size availableSize)
       at System.Windows.FrameworkElement.MeasureOverride(IntPtr nativeTarget, Single inWidth, Single inHeight, Single& outWidth, Single& outHeight)
  InnerException: System.ArgumentException
       Message=The parameter is incorrect. 
       StackTrace:
            at MS.Internal.XcpImports.CheckHResult(UInt32 hr)
            at MS.Internal.XcpImports.SetValue(INativeCoreTypeWrapper obj, DependencyProperty property, DependencyObject doh)
            at MS.Internal.XcpImports.SetValue(INativeCoreTypeWrapper doh, DependencyProperty property, Object obj)
            at System.Windows.DependencyObject.SetObjectValueToCore(DependencyProperty dp, Object value)
            at System.Windows.DependencyObject.SetValueInternal(DependencyProperty dp, Object value, Boolean allowReadOnlySet, Boolean isSetByStyle, Boolean isSetByBuiltInStyle, PropertyInvalidationReason reason)
            at System.Windows.DependencyObject.SetValueInternal(DependencyProperty dp, Object value)
            at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
            at System.Windows.Controls.ContentControl.set_Content(Object value)
            at System.Windows.Controls.ItemsControl.PrepareContainerForItemOverride(DependencyObject element, Object item)
            at System.Windows.Controls.Primitives.Selector.PrepareContainerForItemOverride(DependencyObject element, Object item)
            at System.Windows.Controls.ItemsControl.MS.Internal.Controls.IGeneratorHost.PrepareItemContainer(DependencyObject container, Object item)
            at System.Windows.Controls.ItemContainerGenerator.System.Windows.Controls.Primitives.IItemContainerGenerator.PrepareItemContainer(DependencyObject container)
            at System.Windows.Controls.ItemsControl.AddVisualChild(Int32 index, DependencyObject container, Boolean needPrepareContainer)
            at System.Windows.Controls.ItemsControl.AddContainers()
            at System.Windows.Controls.ItemsControl.RecreateVisualChildren(IntPtr unmanagedObj)
            at MS.Internal.XcpImports.MethodExNative(IntPtr context, IntPtr element, UInt32 cString, String name, UInt32 cParams, IntPtr pParams, CValue& outval, Int32& typeIndex)
            at MS.Internal.XcpImports.MethodEx(IntPtr ptr, String name, CValue[] cvData)
            at MS.Internal.XcpImports.MethodEx(DependencyObject obj, String name)
            at MS.Internal.XcpImports.FrameworkElement_ApplyTemplate(FrameworkElement frameworkElement)
            at System.Windows.FrameworkElement.ApplyTemplateInternal()
            at System.Windows.Controls.ScrollContentPresenter.HookupScrollingComponents()
            at System.Windows.Controls.ScrollContentPresenter.OnApplyTemplate()
            at System.Windows.FrameworkElement.OnApplyTemplate(IntPtr nativeTarget)
            at MS.Internal.XcpImports.MeasureNative(IntPtr element, Single inWidth, Single inHeight)
            at MS.Internal.XcpImports.UIElement_Measure(UIElement element, Size availableSize)
            at System.Windows.UIElement.Measure(Size availableSize)
            at System.Windows.Controls.ScrollViewer.MeasureOverride(Size constraint)
            at System.Windows.FrameworkElement.MeasureOverride(IntPtr nativeTarget, Single inWidth, Single inHeight, Single& outWidth, Single& outHeight)
            at MS.Internal.XcpImports.MeasureOverrideNative(IntPtr element, Single inWidth, Single inHeight, Single& outWidth, Single& outHeight)
            at MS.Internal.XcpImports.FrameworkElement_MeasureOverride(FrameworkElement element, Size availableSize)
            at System.Windows.FrameworkElement.MeasureOverride(Size availableSize)
            at System.Windows.FrameworkElement.MeasureOverride(IntPtr nativeTarget, Single inWidth, Single inHeight, Single& outWidth, Single& outHeight)

它说明该元素已经是另一个元素的子元素。

但如果我删除最后一项，并在选择器中只保留五项，它就可以正常工作。我到底搞错了什么？

Answer 1

将ListPicker的ItemCountThreshold属性设置为大于6的值(默认情况下，它列出five或更少的items)。您需要类似于以下内容的内容：

 <toolkit:ListPicker ItemCountThreshold="10">
                <toolkit:ListPickerItem Content="1" />
                <toolkit:ListPickerItem Content="2"/>
                <toolkit:ListPickerItem Content="3"/>
                <toolkit:ListPickerItem Content="4"/>
                <toolkit:ListPickerItem Content="5"/>
                <toolkit:ListPickerItem Content="6"/>
            </toolkit:ListPicker>

ItemCountThreshold：ItemCountThreshold是int类型的依赖属性。它指定将在展开模式下显示的最大项目数。默认情况下，包含五个或更少项目的列表就地展开，而包含更多项目的列表切换到全屏选择界面。也可以将其设置为0以切换全模式，或设置为非常大的数字以切换扩展模式。

Answer 2

我永远不能使用ListPickerItem让ListPicker工作，也不能将ItemCountThreshold=设置为0。其文档表明，当值设置为零时，full模式应自动发生。不要相信它。它不起作用。

在切换到使用列表绑定的代码后，它终于可以工作了。当它可以使用声明性XAML简单地解决时，为什么要采取困难的方式(代码隐藏)呢？希望ListPickerItem能尽快修好。

Answer 3

在最新版本的工具包中，ItemCountThreshold现在是一个只读属性。没有简单的方法来切换到超过5个项目的内联扩展。