CODEWITHSUNDEEP
c#wpfcomboboxnullreferenceexception
pingu2k4
pingu2k4

Reputation: 1050

Recieving null reference exception when clicking combobox?

I want a list of items to appear in my combobox, each item should be an image followed by some text. I am adding 1 item at the moment to my list (I previously held it as an observiablecollection but same problem).

Here is my combobox:

<ComboBox Grid.Row="0" ItemsSource="{Binding CrewComboSource}" SelectedValue="{Binding Crew01S}" Margin="2,0">
    <ComboBox.ItemTemplate>
        <DataTemplate>
            <StackPanel Orientation="Horizontal">
                <Image Source="{Binding Image}" Width="30"/>
                <TextBlock Text="{Binding Name}" FontStyle="Bold"/>
            </StackPanel>
        </DataTemplate>
    </ComboBox.ItemTemplate>
</ComboBox>

I have a class here:

class CrewCombo
{
    public string Name
    {
        get;
        set;
    }

    public string Image
    {
        get;
        set;
    }
}

And initialising stuff here:

CrewComboSource = new List<CrewCombo>();
CrewCombo tempCrewMember = new CrewCombo();
tempCrewMember.Name = "test";
tempCrewMember.Image = AppDomain.CurrentDomain.BaseDirectory + "Media\\POP\\Wisp.png";
CrewComboSource.Add(tempCrewMember);

The image displays correctly when using:

<Image Grid.Row="1" HorizontalAlignment="Center" Source="{Binding CrewComboSource[0].Image}" Width="30" />

Exception info:

A first chance exception of type 'System.Windows.Markup.XamlParseException' occurred in PresentationFramework.dll

Additional information: Provide value on 'System.Windows.Baml2006.TypeConverterMarkupExtension' threw an exception.

A first chance exception of type 'System.Windows.Markup.XamlParseException' occurred in PresentationFramework.dll

Additional information: Provide value on 'System.Windows.Baml2006.TypeConverterMarkupExtension' threw an exception.

An unhandled exception of type 'System.NullReferenceException' occurred in PresentationFramework.dll

Additional information: Object reference not set to an instance of an object.

If I edit my XAML, such that the image and textblock within the stackpanel in datatemplate are non existent, so it is open stackpanel, comment, comment, end stackpanel then I don't get this issue (but obviously I don't get anything in the combobox either). De-commenting EITHER the textblock or the image reintroduces the exception.

Upvotes: 0

Views: 811

Answers (1)

pingu2k4
pingu2k4

Reputation: 1050

I don't know what fixed it... But I rewrote the XAML by hand, 1 step at a time and it now works fine... Its strange. I think the XAML I ended up with is identical???

<ComboBox Grid.Row="0" ItemsSource="{Binding CrewComboSource}" SelectedValue="{Binding Crew01S}" Margin="2,0">
    <ComboBox.ItemTemplate>
        <DataTemplate>
            <StackPanel Orientation="Horizontal">
                <Image Source="{Binding Image}" Width="30"/>
                <TextBlock Text="{Binding Name}" FontWeight="Bold"/>
            </StackPanel>
        </DataTemplate>
    </ComboBox.ItemTemplate>
</ComboBox>

Anyways, it now works correctly... No idea why. :/ Would still be interested in hearing why this might have happened?

Upvotes: 0

Related Questions