ListPicker crash

I have a ListPicker with the following structure:

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>
开发者_StackOverflow

The following message comes whenever I try to run this:

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)

It says that the element is already a child of another one.

But if I remove the last item and keep only five items in the picker, it works fine. What am I getting wrong?

Set the ItemCountThreshold property of the ListPicker to greater that 6 value (by default it lists with five or fewer items). You need something like for example:

 <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 is a dependency property of type int. It specifies the maximum number of items that will be displayed in Expanded mode. By default, lists with five or fewer items expand in-place while lists with more items switch to a full-screen selection interface. It can also be set to 0 to switch Full mode or a very large number to switch Expanded mode.

I couldn't never make the ListPicker work using ListPickerItem and set ItemCountThreshold="0". Its documentation indicates when the value is set to zero, the full mode should happen automatically. Do not believe it. It does NOT work.

After switched using the code behind with list binding, it finally worked. Why do the hard way (code behind) when it can be simply resolved using the declarative XAML? Hope the ListPickerItem fixed soon.

ItemCountThreshold is now a readonly property in the latest version of the toolkit. There is no easy way to switch to inline expansion with more than 5 items.