[Solved] NullReference exception when clicking in a GridViewComboBoxColumn

[Håkan]

Hi!

I have a GridView declared as this:

<telerik:RadGridView x:Name="DataGrid"
                         ItemsSource="{Binding Shifts, Source={StaticResource ViewModel}}"
                         SelectedItem="{Binding CurrentShift, Source={StaticResource ViewModel}, Mode=TwoWay}"
                         RowIndicatorVisibility="Collapsed" IsFilteringAllowed="False" ShowColumnFooters="False" ShowInsertRow="False"
                         ActionOnLostFocus="CommitEdit" EditTriggers="CellClick"
                         ValidatesOnDataErrors="None"
                         EnableRowVirtualization="False"
                         AutoGenerateColumns="False"
                         RowLoaded="DataGrid_RowLoaded" SelectionChanged="DataGrid_SelectionChanged" AddingNewDataItem="DataGrid_AddingNewDataItem" PreparingCellForEdit="DataGrid_PreparingCellForEdit" RowEditEnded="DataGrid_RowEditEnded">
            <telerik:RadGridView.Resources>
                <Style TargetType="telerik:RadComboBox">
                    <Setter Property="Width" Value="148" />
                    <Setter Property="IsEditable" Value="True" />
                    <Setter Property="TextSearchMode" Value="Contains" />
                    <Setter Property="IsReadOnly" Value="True" />
                    <Setter Property="OpenDropDownOnFocus" Value="True" />
                </Style>
            </telerik:RadGridView.Resources>

            <telerik:RadGridView.Columns>
                <telerik:GridViewDataColumn Header="Rast" Width="40" IsResizable="False">
                    <telerik:GridViewDataColumn.CellTemplate>
                        <DataTemplate>
                            <soe:SOECheckBox IsChecked="{Binding IsBreak, Mode=TwoWay}" Style="{StaticResource GridView_CheckBox}" />
                        </DataTemplate>
                    </telerik:GridViewDataColumn.CellTemplate>
                </telerik:GridViewDataColumn>
                <telerik:GridViewDataColumn Header="Från" DataMemberBinding="{Binding ActualStart}" Width="45" IsResizable="False">
                    <telerik:GridViewDataColumn.CellTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding ActualStart, Converter={StaticResource TimeConverter}}" TextAlignment="Right" />
                        </DataTemplate>
                    </telerik:GridViewDataColumn.CellTemplate>
                    <telerik:GridViewDataColumn.CellEditTemplate>
                        <DataTemplate>
                            <soe:SOETextBox Text="{Binding ActualStart, Mode=TwoWay, Converter={StaticResource TimeConverter}}" IsTime="True" Width="44" TextAlignment="Right" TimeChanged="StartChanged" />
                        </DataTemplate>
                    </telerik:GridViewDataColumn.CellEditTemplate>
                </telerik:GridViewDataColumn>
                <telerik:GridViewDataColumn Header="Till" DataMemberBinding="{Binding ActualEnd}" Width="45" IsResizable="False">
                    <telerik:GridViewDataColumn.CellTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding ActualEnd, Converter={StaticResource TimeConverter}}" TextAlignment="Right" />
                        </DataTemplate>
                    </telerik:GridViewDataColumn.CellTemplate>
                    <telerik:GridViewDataColumn.CellEditTemplate>
                        <DataTemplate>
                            <soe:SOETextBox Text="{Binding ActualEnd, Mode=TwoWay, Converter={StaticResource TimeConverter}}" IsTime="True" Width="44" TextAlignment="Right" TimeChanged="EndChanged" />
                        </DataTemplate>
                    </telerik:GridViewDataColumn.CellEditTemplate>
                </telerik:GridViewDataColumn>
                <telerik:GridViewDataColumn Header="Längd" Width="45" IsResizable="False" IsReadOnly="True">
                    <telerik:GridViewDataColumn.CellTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding Path=., Converter={StaticResource TimeScheduleShiftLengthConverter}}" TextAlignment="Right" />
                        </DataTemplate>
                    </telerik:GridViewDataColumn.CellTemplate>
                </telerik:GridViewDataColumn>
                <telerik:GridViewComboBoxColumn Header="Passtyp" IsComboBoxEditable="True" DataMemberBinding="{Binding ShiftTypeId}" ItemsSource="{Binding Path=ShiftTypes, Source={StaticResource ViewModel}}" SelectedValueMemberPath="ShiftTypeId" DisplayMemberPath="Name" Width="150">
                    <telerik:GridViewComboBoxColumn.CellTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding ShiftTypeName}" />
                        </DataTemplate>
                    </telerik:GridViewComboBoxColumn.CellTemplate>
                    <telerik:GridViewComboBoxColumn.CellEditTemplate>
                        <DataTemplate>
                            <telerik:RadComboBox SelectedValue="{Binding ShiftTypeId, Mode=TwoWay}" ItemsSource="{Binding Path=ShiftTypes, Source={StaticResource ViewModel}}" SelectedValuePath="ShiftTypeId" DisplayMemberPath="Name" SelectionChanged="ShiftType_SelectionChanged">
                                <telerik:RadComboBox.ItemsPanel>
                                    <ItemsPanelTemplate>
                                        <VirtualizingStackPanel Width="250" />
                                    </ItemsPanelTemplate>
                                </telerik:RadComboBox.ItemsPanel>
                            </telerik:RadComboBox>
                        </DataTemplate>
                    </telerik:GridViewComboBoxColumn.CellEditTemplate>
                </telerik:GridViewComboBoxColumn>
                <telerik:GridViewComboBoxColumn Header="Schematyp" IsComboBoxEditable="True" DataMemberBinding="{Binding TimeScheduleTypeId}" ItemsSource="{Binding Path=TimeScheduleTypes, Source={StaticResource ViewModel}}" SelectedValueMemberPath="TimeScheduleTypeId" DisplayMemberPath="Name" Width="150" IsVisible="{Binding ShowTimeScheduleType}">
                    <telerik:GridViewComboBoxColumn.CellTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding TimeScheduleTypeName}" />
                        </DataTemplate>
                    </telerik:GridViewComboBoxColumn.CellTemplate>
                    <telerik:GridViewComboBoxColumn.CellEditTemplate>
                        <DataTemplate>
                            <telerik:RadComboBox SelectedValue="{Binding TimeScheduleTypeId, Mode=TwoWay}" ItemsSource="{Binding Path=TimeScheduleTypes, Source={StaticResource ViewModel}}" SelectedValuePath="TimeScheduleTypeId" DisplayMemberPath="Name" SelectionChanged="TimeScheduleType_SelectionChanged">
                                <telerik:RadComboBox.ItemsPanel>
                                    <ItemsPanelTemplate>
                                        <VirtualizingStackPanel Width="250" />
                                    </ItemsPanelTemplate>
                                </telerik:RadComboBox.ItemsPanel>
                            </telerik:RadComboBox>
                        </DataTemplate>
                    </telerik:GridViewComboBoxColumn.CellEditTemplate>
                </telerik:GridViewComboBoxColumn>
                <telerik:GridViewComboBoxColumn Header="Anställd" IsComboBoxEditable="True" DataMemberBinding="{Binding EmployeeId}" ItemsSource="{Binding Path=Employees, Source={StaticResource ViewModel}}" SelectedValueMemberPath="Key" DisplayMemberPath="Value" Width="150" IsVisible="{Binding ShowEmployeeInGridView}">
                    <telerik:GridViewComboBoxColumn.CellTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding EmployeeName}" />
                        </DataTemplate>
                    </telerik:GridViewComboBoxColumn.CellTemplate>
                    <telerik:GridViewComboBoxColumn.CellEditTemplate>
                        <DataTemplate>
                            <telerik:RadComboBox SelectedValue="{Binding EmployeeId, Mode=TwoWay}" ItemsSource="{Binding Path=Employees, Source={StaticResource ViewModel}}" SelectedValuePath="Key" DisplayMemberPath="Value" SelectionChanged="Employee_SelectionChanged">
                                <telerik:RadComboBox.ItemsPanel>
                                    <ItemsPanelTemplate>
                                        <VirtualizingStackPanel Width="250" />
                                    </ItemsPanelTemplate>
                                </telerik:RadComboBox.ItemsPanel>
                            </telerik:RadComboBox>
                        </DataTemplate>
                    </telerik:GridViewComboBoxColumn.CellEditTemplate>
                </telerik:GridViewComboBoxColumn>
                <telerik:GridViewColumn Width="26" IsReadOnly="True" TabStopMode="Skip" IsResizable="False" IsVisible="{Binding IsReadOnly, ElementName=DataGrid, Converter={StaticResource BooleanInvertConverter}}">
                    <telerik:GridViewColumn.CellTemplate>
                        <DataTemplate>
                            <soe:RadImageButton Style="{StaticResource GridViewDeleteRowButton}" Command="telerikGrid:RadGridViewCommands.Delete" CommandParameter="{Binding}" />
                        </DataTemplate>
                    </telerik:GridViewColumn.CellTemplate>
                </telerik:GridViewColumn>
            </telerik:RadGridView.Columns>
        </telerik:RadGridView>

As you can see there are three combobox columns and the first two works fine, but when I click or tab into the third (with Header="Anställd") I get the following exception:
Object reference not set to an instance of an object.

   at Telerik.Windows.Controls.GridView.GridViewCell.SetCellElement()
   at Telerik.Windows.Controls.GridView.GridViewCell.HideEditor()
   at Telerik.Windows.Controls.GridView.GridViewCell.ToggleEditor()
   at Telerik.Windows.Controls.GridView.GridViewDataControl.OnCellEditModeChanged(GridViewCell cell, Boolean newIsInEditMode)
   at Telerik.Windows.Controls.GridView.GridViewCell.IsInEditModeChanged(DependencyObject target, DependencyPropertyChangedEventArgs e)
   at System.Windows.DependencyObject.RaisePropertyChangeNotifications(DependencyProperty dp, Object oldValue, Object newValue)
   at System.Windows.DependencyObject.UpdateEffectiveValue(DependencyProperty property, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, ValueOperation operation)
   at System.Windows.DependencyObject.SetValueInternal(DependencyProperty dp, Object value, Boolean allowReadOnlySet, Boolean isBindingInStyleSetter)
   at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
   at Telerik.Windows.Controls.GridView.GridViewCell.set_IsInEditMode(Boolean value)
   at Telerik.Windows.Controls.GridView.GridViewCell.UpdateOnIsCurrentChanged(Boolean newValue)
   at Telerik.Windows.Controls.GridView.GridViewCell.IsCurrentChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
   at Telerik.Windows.PropertyMetadata.PropertyChangeHook.OnPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
   at System.Windows.DependencyObject.RaisePropertyChangeNotifications(DependencyProperty dp, Object oldValue, Object newValue)
   at System.Windows.DependencyObject.UpdateEffectiveValue(DependencyProperty property, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, ValueOperation operation)
   at System.Windows.DependencyObject.SetValueInternal(DependencyProperty dp, Object value, Boolean allowReadOnlySet, Boolean isBindingInStyleSetter)
   at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
   at Telerik.Windows.Controls.GridView.GridViewCell.set_IsCurrent(Boolean value)
   at Telerik.Windows.Controls.GridView.GridViewDataControl.set_CurrentCellInfo(GridViewCellInfo value)
   at Telerik.Windows.Controls.GridView.GridViewCell.OnGotFocus(RoutedEventArgs e)
   at System.Windows.Controls.Control.OnGotFocus(Control ctrl, EventArgs e)
   at MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr unmanagedObjArgs, Int32 argsTypeIndex, Int32 actualArgsTypeIndex, String eventName, UInt32 flags)

The exception is not handled anywhere and I end up in the Application_UnhandledException method in App.xaml.cs.
I don't know where to look, the code worked before, but there must be some modification I have made, but I don't know where.
Do you have any tip on where to start looking?

Regards,
Håkan

[Pavel Pavlov]

Hi,
Using only the xaml provided I was not able to reproduce the issue.
May be you should check your DataGrid_PreparingCellForEdit event handler.

If this does not help , I may need to perform a small debugging session over a runnable project.

Regards,
Pavel Pavlov
Telerik