Null exception in XAML [closed]

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This isn't so much a problem, but rather an annoyance... I've put together a conditional class to show different views dependent on which radio button is selected. It works as expected, but I can't get rid of the blue squiggle under my 'SwitchCase' property.

Case class:

public class Case : ContentControl
{
    public static readonly DependencyProperty SwitchCaseProperty = DependencyProperty.Register("SwitchCase",
      typeof(object), typeof(Case), new PropertyMetadata() { PropertyChangedCallback = OnPropChanged });

    public object? SwitchCase
    {
        get => GetValue(SwitchCaseProperty);
        set => SetValue(SwitchCaseProperty, value);
    }

    public object? SwitchValue { get; set; }
    public object? SwitchContent { get; set; }

    private static void OnPropChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (d is Case _case)
        {
            _case.Content = _case.SwitchCase.ToString() == _case.SwitchValue.ToString() ? _case.SwitchContent : null;
        }
    }
}

Implementation:

<Grid Grid.Row="1"
      TextElement.Foreground="#c2c2c2">
    <conditional:Case SwitchCase="{Binding ElementName=HomeNavButton, Path=IsChecked}"
                      SwitchValue="True"
                      SwitchContent="{StaticResource HomeView}" />
    <conditional:Case SwitchCase="{Binding ElementName=AccountNavButton, Path=IsChecked}"
                      SwitchValue="True"
                      SwitchContent="{StaticResource AccountView}" />
    <conditional:Case SwitchCase="{Binding ElementName=UserNavButton, Path=IsChecked}"
                      SwitchValue="True"
                      SwitchContent="{StaticResource LoginView}" />
</Grid>

It runs fine, but I can't see why the null exception applies when all 3 'navbuttons' exist.

Any ideas?

Edit

The following error appears on each of the SwitchCase statements in xaml editor:

Case.SwitchCase
Object reference not set to an instance of an object

Please edit your question to include a more detailed description of the problem you have. Hover over the "blue squiggle" and post the full complete error/warning/info message you get. You can also check the error list to see any error/warning/info you get. — Progman
– Progman, Commented Jul 19 at 19:28
Currently working on C# WPF .Net Core application. The reason I'm using object is so that this can be more generic. The binding could be anything, and the value could be anything. — Richard Harrison
– Richard Harrison, Commented Jul 19 at 19:40

Richard Harrison · Accepted Answer · 2025-07-19 20:38:41Z

1

It turns out that I missed the null checking in the Case class.

private static void OnPropChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    if (d is Case _case && _case.SwitchCase != null && _case.SwitchValue != null)
    {
        _case.Content = _case.SwitchCase.ToString() == _case.SwitchValue.ToString() ? _case.SwitchContent : null;
    }
}

answered Jul 19 at 20:38

Richard Harrison

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