Binding to ComboBox with converter in Silverlight - wpf

Question

I have a numeric value that I wish to be converted to a more user-friendly string format when it's displayed. I already have an IValueConverter called FlightLevelConverter that I'm using to do this for a normal TextBlock UI item where it works fine.
I now wish to apply the converter to a ComboBox of altitude choices, but I can't get it to work.
This is the relevant part of the XAML I'm using for the ComboBox:
<UserControl.Resources>
<status:FlightLevelConverter x:Key="FlightLevelConverter"/>
</UserControl.Resources>
...
<ComboBox x:Name="AltitudeCombo" Grid.Row="0" Grid.Column="3" Width="100">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Converter={StaticResource FlightLevelConverter}}"/>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
It displays the un-converted numeric values, not the nice string values. I get no errors and if I set a breakpoint in the converter it doesn't get hit, showing that the converter is never called.
I've spent all morning trawling the Internet in general and StackOverflow in particular to try to discover what I'm doing wrong, but haven't found out anything useful.
Why is my converter not being called? What am I doing wrong?

Answer 1

How do you add the items to the ComboBox?
You should set the ItemsSource property to a collection of numeric values, e.g.
List<double> values = new List<double>();
values.Add(2.1);
values.Add(3.2);
values.Add(4.3);
values.Add(5.4);
AltitudeCombo.ItemsSource = values;
If you add ComboBoxItems like this
AltitudeCombo.Items.Add(new ComboBoxItem() { Content = 1.4 });
the ItemTemplate and hence the binding with its converter won't be applied.

Answer 2

Here is a short working sample. You can compare code...
XAML:
<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:bys="clr-namespace:WpfApplication1"
xmlns:sys="clr-namespace:System;assembly=mscorlib"
Title="MainWindow" Height="350" Width="525">
<Grid>
<Grid.Resources>
<bys:MyList x:Key="lst"/>
<bys:MyConverter x:Key="myConverter"/>
</Grid.Resources>
<ComboBox ItemsSource="{StaticResource lst}" SelectedIndex="0">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Converter={StaticResource myConverter}}"/>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox >
</Grid>
</Window>
C#:
public class MyList : List<int> {
public MyList() {
AddRange(new[] { 1, 2, 3, 4, 5, 6 });
}
}
public class MyConverter : IValueConverter {
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
return String.Format("<<{0}>>", value);
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
throw new NotImplementedException();
}
}

Answer 3

ComboBox.ItemTemplate is not applicable to the main part of the ComboBox if ComboBox.IsEditable == true. It works for dropdown list entries only. Try to set ComboBox.IsEditable == false. It might help.