Wpf- Unable to cast MenuItem to Listbox?

Question

I am getting a very strange exception. I get the exception:

"'Set connectionId threw an exception.' Line number '26' and line position '34'."

When I look at the Inner Exception I get:

"Unable to cast object of type 'System.Windows.Controls.MenuItem' to type 'System.Windows.Controls.ListBox'."

I have narrowed the cause of the exception to the MenuItem in the TreeViewItem style contained in this TreeView:

<TreeView x:Name="ProjectElementTreeView" ItemsSource="{Binding ProjectElementCollection}"  DisplayMemberPath="Name" Padding="0" SelectedItemChanged="ProjectElementTreeView_SelectedItemChanged" GotKeyboardFocus="ProjectElementTreeView_GotKeyboardFocus">
        <TreeView.Resources>
            <Style TargetType="{x:Type TreeViewItem}">
                <Setter Property="HorizontalAlignment" Value="Left" />
                <Setter Property="ContextMenu">
                    <Setter.Value>
                        <ContextMenu>
                            <MenuItem Name="AddProjectElementMenuItem" Header="Add" Click="AddProjectElementMenuItem_Click"/>
                        </ContextMenu>
                    </Setter.Value>
                </Setter>
            </Style>
        </TreeView.Resources>
    </TreeView>

The exception only occurs when the MenuItem has a click event handler and is thrown even when the click event handler does not contain any code.

Answer 1

I got the same exception as you did. After looking closer at the code, this feels like a situation where you would get

"The event 'Click' cannot be specified on a Target tag in a Style. Use an EventSetter instead."

I'm not sure why that doesn't apply here.
Anyway, using an EventSetter works

<Setter Property="ContextMenu">
    <Setter.Value>
        <ContextMenu>
            <MenuItem Name="AddProjectElementMenuItem" Header="Add">
                <MenuItem.Style>
                    <Style TargetType="MenuItem">
                        <EventSetter Event="Click" Handler="AddProjectElementMenuItem_Click"/>
                    </Style>
                </MenuItem.Style>
            </MenuItem>
        </ContextMenu>
    </Setter.Value>
</Setter>

Answer 2

I had to face this weird situation myself. There is an easy way to get over it, you have to clean and rebuild the project and the exception will go away.

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Hope this helps.