CalendarItem template causing NullReferenceExeption

Question

I created my own calendar and datepicker control before they were released and am now mobing to .Net 4.0. I decided to go with the controls provided in WPF 4.0 but I am trying to create my own style for the calendar and not having much luck so far. I have created many styles for most controls provided and I like to open the default styles in Relfector and basically just modify them using it as a base. Unfortunately, the one provided for the Calendar control contained many errors when I copied it mainly due to VisualState tags but I figured they were optional and removed them, much like event or data triggers that change the visual appearance.

At first it seemed as though it worked but when I hovered the previous, next or header button it crashed giving a NullReferenceExeption. I figured it was due to removing the visual states and got a template from the net someone has used. Unfortunately, it was for the Calendar control in the WpfToolkit, but I made the modifications and the header button works. When I click it I get the Year view and again to get the Decade view. However, when I click to go to the month view or click the next/previous month view I get the a NullReferenceExeption. I have no idea what is causing the error as it is inside a framework DLL and consequently have no idea how to fix it. I tried to add VisualStates thinking it was trying to apply a visual state that I did not specify. I also tried opening the Calendar control code in Reflector to get an idea of what is causing the error. Here is my template so far:

<Window x:Class="MainWindow"

 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

 Title="MainWindow" Height="350" Width="525">

 

 <Grid>

  

  

  

  <Calendar xmlns:vsm="clr-namespace:System.Windows;assembly=PresentationFramework">

   <Calendar.CalendarItemStyle>

    <Style TargetType="CalendarItem">

     <Setter Property="Template">

      <Setter.Value>

       <ControlTemplate TargetType="CalendarItem">

        <ControlTemplate.Resources>

         <DataTemplate x:Key="DayTitleTemplate">

          <TextBlock Text="{Binding}"

           HorizontalAlignment="Center" />

         </DataTemplate>

        </ControlTemplate.Resources>



        <DockPanel Name="PART_Root" LastChildFill="True">

         <vsm:VisualStateManager.VisualStateGroups>

          <vsm:VisualStateGroup x:Name="CommonStates">

           <vsm:VisualState x:Name="Normal" />

           <vsm:VisualState x:Name="Disabled">

            <Storyboard>

             <DoubleAnimation Storyboard.TargetName="PART_DisabledVisual" Storyboard.TargetProperty="Opacity" To="1" Duration="0" />

            </Storyboard>

           </vsm:VisualState>

          </vsm:VisualStateGroup>

         </vsm:VisualStateManager.VisualStateGroups>



         <Button x:Name="PART_PreviousButton" DockPanel.Dock="Left" Content="&lt;" Focusable="False">

          <Button.Template>

           <ControlTemplate TargetType="Button">

            <Grid Cursor="Hand">

             <vsm:VisualStateManager.VisualStateGroups>

              <vsm:VisualStateGroup x:Name="CommonStates">

               <vsm:VisualState x:Name="Normal" />

               <vsm:VisualState x:Name="MouseOver">

                <Storyboard>

                 <ColorAnimation Storyboard.TargetName="TextColor" Storyboard.TargetProperty="Color" To="#FF73A9D8" Duration="0" />

                </Storyboard>

               </vsm:VisualState>

               <vsm:VisualState x:Name="Disabled">

                <Storyboard>

                 <DoubleAnimation Storyboard.TargetName="TextColor" Storyboard.TargetProperty="Opacity" To=".5" Duration="0" />

                </Storyboard>

               </vsm:VisualState>

              </vsm:VisualStateGroup>

             </vsm:VisualStateManager.VisualStateGroups>

             <Rectangle Fill="#11E5EBF1" Stretch="Fill" Opacity="1"/>

             <Grid>

              <Path Margin="14,-6,0,0" Height="10" Width="6" VerticalAlignment="Center" HorizontalAlignment="Left" Stretch="Fill" Data="M288.75,232.25 L288.75,240.625 L283,236.625 z">

               <Path.Fill>

                <SolidColorBrush x:Name="TextColor" Color="#FF333333" />

               </Path.Fill>

              </Path>

             </Grid>

            </Grid>

           </ControlTemplate>



          </Button.Template>

         </Button>



         <Button x:Name="PART_NextButton" DockPanel.Dock="Right" Content="&gt;" Focusable="False">

          <Button.Template>

           <ControlTemplate TargetType="Button">

            <Grid Cursor="Hand">

             <vsm:VisualStateManager.VisualStateGroups>

              <vsm:VisualStateGroup x:Name="CommonStates">

               <vsm:VisualState x:Name="Normal" />

               <vsm:VisualState x:Name="MouseOver">

                <Storyboard>

                 <ColorAnimation Storyboard.TargetName="TextColor" Storyboard.TargetProperty="Color" To="#FF73A9D8" Duration="0" />

                </Storyboard>

               </vsm:VisualState>

               <vsm:VisualState x:Name="Disabled">

                <Storyboard>

                 <DoubleAnimation Storyboard.TargetName="TextColor" Storyboard.TargetProperty="Opacity" To=".5" Duration="0" />

                </Storyboard>

               </vsm:VisualState>

              </vsm:VisualStateGroup>

             </vsm:VisualStateManager.VisualStateGroups>

             <Rectangle Fill="#11E5EBF1" Stretch="Fill" Opacity="1"/>

             <Grid>

              <Path Margin="0,-6,14,0" Height="10" Width="6" VerticalAlignment="Center" HorizontalAlignment="Right" Stretch="Fill" Data="M282.875,231.875 L282.875,240.375 L288.625,236 z">

               <Path.Fill>

                <SolidColorBrush x:Name="TextColor" Color="#FF333333" />

               </Path.Fill>

              </Path>

             </Grid>

            </Grid>

           </ControlTemplate>

          </Button.Template>

         </Button>



         <Button x:Name="PART_HeaderButton" DockPanel.Dock="Top" FontWeight="Bold" Focusable="False">

          <Button.Template>

           <ControlTemplate TargetType="Button">

            <Grid Cursor="Hand">

             <vsm:VisualStateManager.VisualStateGroups>

              <vsm:VisualStateGroup x:Name="CommonStates">

               <vsm:VisualState x:Name="Normal" />

               <vsm:VisualState x:Name="MouseOver">

                <Storyboard>

                 <ColorAnimation Storyboard.TargetName="TextColor" Storyboard.TargetProperty="Color" To="#FF73A9D8" Duration="0" />

                </Storyboard>

               </vsm:VisualState>

               <vsm:VisualState x:Name="Disabled">

                <Storyboard>

                 <DoubleAnimation Storyboard.TargetName="buttonContent" Storyboard.TargetProperty="Opacity" To=".5" Duration="0" />

                </Storyboard>

               </vsm:VisualState>

              </vsm:VisualStateGroup>

             </vsm:VisualStateManager.VisualStateGroups>

             <ContentPresenter x:Name="buttonContent" Content="{TemplateBinding Content}"

																						ContentTemplate="{TemplateBinding ContentTemplate}" Margin="1,4,1,9"

																						HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"

																						VerticalAlignment="{TemplateBinding VerticalContentAlignment}">

              <TextElement.Foreground>

               <SolidColorBrush x:Name="TextColor" Color="#FF333333"/>

              </TextElement.Foreground>

             </ContentPresenter>

            </Grid>

           </ControlTemplate>

          </Button.Template>

         </Button>



         <Grid>

          <Grid x:Name="PART_MonthView" 

          Visibility="Visible">

           <Grid.RowDefinitions>

            <RowDefinition Height="Auto"/>

            <RowDefinition Height="Auto"/>

            <RowDefinition Height="Auto"/>

            <RowDefinition Height="Auto"/>

            <RowDefinition Height="Auto"/>

            <RowDefinition Height="Auto"/>

            <RowDefinition Height="Auto"/>

           </Grid.RowDefinitions>

           <Grid.ColumnDefinitions>

            <ColumnDefinition Width="Auto"/>

            <ColumnDefinition Width="Auto"/>

            <ColumnDefinition Width="Auto"/>

            <ColumnDefinition Width="Auto"/>

            <ColumnDefinition Width="Auto"/>

            <ColumnDefinition Width="Auto"/>

            <ColumnDefinition Width="Auto"/>

           </Grid.ColumnDefinitions>

          </Grid>



          <Grid x:Name="PART_YearView" 

          Visibility="Hidden">

           <Grid.RowDefinitions>

            <RowDefinition Height="Auto"/>

            <RowDefinition Height="Auto"/>

            <RowDefinition Height="Auto"/>

           </Grid.RowDefinitions>

           <Grid.ColumnDefinitions>

            <ColumnDefinition Width="Auto"/>

            <ColumnDefinition Width="Auto"/>

            <ColumnDefinition Width="Auto"/>

            <ColumnDefinition Width="Auto"/>

           </Grid.ColumnDefinitions>

          </Grid>

         </Grid>

         <Rectangle x:Name="PART_DisabledVisual" Opacity="0" Visibility="Collapsed" Fill="#A5FFFFFF"/>

        </DockPanel>

        <ControlTemplate.Triggers>

         <Trigger Property="IsEnabled" Value="False">

          <Setter TargetName="PART_DisabledVisual" Property="Visibility" Value="Visible"></Setter>

         </Trigger>



         <DataTrigger Binding="{Binding Path=DisplayMode, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Calendar}}" Value="Year">

          <Setter TargetName="PART_MonthView" Property="Visibility" Value="Hidden"></Setter>

          <Setter TargetName="PART_YearView" Property="Visibility" Value="Visible"></Setter>

         </DataTrigger>



         <DataTrigger Binding="{Binding Path=DisplayMode, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Calendar}}" Value="Decade">

          <Setter TargetName="PART_MonthView" Property="Visibility" Value="Hidden"></Setter>

          <Setter TargetName="PART_YearView" Property="Visibility" Value="Visible"></Setter>

         </DataTrigger>

        </ControlTemplate.Triggers>

       </ControlTemplate>

      </Setter.Value>

     </Setter>

    </Style>

   </Calendar.CalendarItemStyle>

  </Calendar>

  

  

  

 </Grid>

 

</Window>

On a side note, I really don't like VisualStates and if not specifying them is what is causing my exception I think that should be changed. I personally don't like setting the visual state from code when a dependency property with a trigger can do the job (ie. IsEnabled, MouseOver, Pressed). But it seems as though it will become a part of WPF and I think at least valid visual states should be specified somewhere similar to specifying template parts at the top of a control class. However, I will probably still refrain from using them :)

When I click the next button here is the exception detail:

System.NullReferenceException was unhandled
  Message=Object reference not set to an instance of an object.
  Source=PresentationCore
  StackTrace:
       at System.Windows.Automation.Peers.AutomationPeer.EnsureChildren()
       at System.Windows.Automation.Peers.AutomationPeer.GetChildren()
       at System.Windows.Automation.Peers.AutomationPeer.isDescendantOf(AutomationPeer parent)
       at System.Windows.Automation.Peers.AutomationPeer.isDescendantOf(AutomationPeer parent)
       at System.Windows.Automation.Peers.AutomationPeer.ValidateConnected(AutomationPeer connectedPeer)
       at System.Windows.Automation.Peers.AutomationPeer.AutomationPeerFromInputElement(IInputElement focusedElement)
       at System.Windows.Automation.Peers.AutomationPeer.RaiseFocusChangedEventHelper(IInputElement newFocus)
       at System.Windows.Input.KeyboardDevice.ChangeFocus(DependencyObject focus, Int32 timestamp)
       at System.Windows.Input.KeyboardDevice.TryChangeFocus(DependencyObject newFocus, IKeyboardInputProvider keyboardInputProvider, Boolean askOld, Boolean askNew, Boolean forceToNullIfFailed)
       at System.Windows.Input.KeyboardDevice.Focus(DependencyObject focus, Boolean askOld, Boolean askNew, Boolean forceToNullIfFailed)
       at System.Windows.Input.KeyboardDevice.Focus(IInputElement element)
       at System.Windows.UIElement.Focus()
       at System.Windows.Input.KeyboardNavigation.Navigate(DependencyObject currentElement, TraversalRequest request, ModifierKeys modifierKeys, DependencyObject firstElement)
       at System.Windows.FrameworkElement.MoveFocus(TraversalRequest request)
       at System.Windows.Controls.Primitives.CalendarItem.FocusDate(DateTime date)
       at System.Windows.Controls.Calendar.MoveDisplayTo(Nullable`1 date)
       at System.Windows.Controls.Calendar.OnNextClick()
       at System.Windows.Controls.Primitives.CalendarItem.NextButton_Click(Object sender, RoutedEventArgs e)
       at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
       at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
       at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
       at System.Windows.UIElement.RaiseEvent(RoutedEventArgs e)
       at System.Windows.Controls.Primitives.ButtonBase.OnClick()
       at System.Windows.Controls.Button.OnClick()
       at System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp(MouseButtonEventArgs e)
       at System.Windows.UIElement.OnMouseLeftButtonUpThunk(Object sender, MouseButtonEventArgs e)
       at System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
       at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
       at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
       at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
       at System.Windows.UIElement.ReRaiseEventAs(DependencyObject sender, RoutedEventArgs args, RoutedEvent newEvent)
       at System.Windows.UIElement.OnMouseUpThunk(Object sender, MouseButtonEventArgs e)
       at System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
       at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
       at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
       at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
       at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
       at System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
       at System.Windows.UIElement.RaiseEvent(RoutedEventArgs args, Boolean trusted)
       at System.Windows.Input.InputManager.ProcessStagingArea()
       at System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
       at System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
       at System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel)
       at System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
       at System.Windows.Interop.HwndSource.InputFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
       at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
       at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
       at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
       at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
       at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
       at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
       at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
       at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
       at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
       at System.Windows.Threading.Dispatcher.Run()
       at System.Windows.Application.RunDispatcher(Object ignore)
       at System.Windows.Application.RunInternal(Window window)
       at System.Windows.Application.Run(Window window)
       at System.Windows.Application.Run()
       at CalendarStyle.Application.Main() in D:\Users\Manuel\Documents\My Visual Studio Projects\Testing\CalendarStyle\CalendarStyle\obj\x86\Debug\Application.g.vb:line 64
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException:

If I can't get it working I will have to use my own controls instead but hopefully someone can help me to get it working.

 

Answer 1

Hi MannyZanny,

I have tested the code you provided, I have not found any exceptions, could you help me reproduce your issue, and then I will do my best to resolve your issue.

I have upload the source code I tested on my side(no exception), the link is:

http://cid-41e44c402aaada87.office.live.com/self.aspx/For%20MannyZanny/ExceptionTest.rar

 

Best regards,

---

Sheldon _Xiao [MSFT]
MSDN Community Support | Feedback to us
Get or Request Code Sample from Microsoft
Please remember to mark the replies as answers if they help and unmark them if they provide no help.

Answer 2

I tried it on 3 different computers and it works but I have no idea why it won't work on my development PC. I installed Windows Vista Business x64 about 2 months ago and installed Visual Studio 2008 but it seems the .NET framework is somehow malfunctioning. I don't want to reinstall and try to fix the problem since I already have my own calendar that works so I am going to use my custom control instead. I guess it's one of those "It doesn't work on my computer" problems. Thanks for the help anyways.

Manny.

Answer 3

I fixed this same issue in my code a few days ago.

 

Change the DataTemplate from "DayTitleTemplate" to "{x:Static CalendarItem.DayTitleTemplateResourceKey}"

This fixed the issue for me.

I was only able to reproduce it with a machine using UI Automation such as an HP TouchSmart.

 

Good luck.

Timothy McGrath