ListPicker crash

Question

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>

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?

Answer 1

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.