I'm creating as an exercise a WPF custom control to display log messages as in the VS panel (Errors/Warnings/Message). The control is an ItemControl, every item is a message to display. But I have to classify the message in the proper category, so I need each item to expose something ( an interface maybe ) to let the control know how to categorizxe the message. I don't know how to force the Item to be of a certain type, how can I achieve this ? Is the design startegy wrong ? Thanks!
you can inherit your custom control from ItemsControl and create a strongly typed collectional property, then in your control's template put the following line:
<Setter Property="ItemsSource" Value="{Binding MyStronglyTypedCollectionalPropertyName}" />
I do it a lot with ObservableCollections.
The fact that you use ItemsControl doesn't oblige you to use its ItemsSource directly, you can bind to it instead.
P.S. Technically speaking that still leaves a possibility for anyone to go off and set ItemsSource directly bypassing MyStronglyTypedCollectionalPropertyName. Personally I don't think that it's a good idea to throw in that case, but you can check the value type from within OnPropertyChanged:
protected override void OnPropertyChanged(DependencyPropertyChangedEventArgse)
{
if (e.Property == ItemsControl.ItemsSourceProperty && e.NewValue as MySuperTime == null)
{
throw new ArgumentException("ItemsSource value must be of 'MySuperTime' type.");
}
base.OnPropertyChanged(e);
}