Generic Behavior - wpf

Question

I would like create generic behavior. My problem is generic declaration in XAML.
public class GenericBehavior<T> : Behavior<DataGrid>
where T : class
{
}
I can’t use x:TypeArguments because I don’t have loose XAML file.
In WPF and when targeting .NET Framework 4, you can use XAML 2009
features together with x:TypeArguments but only for loose XAML (XAML
that is not markup-compiled). Markup-compiled XAML for WPF and the
BAML form of XAML do not currently support the XAML 2009 keywords and
features
I found some workaround with MarkupExtension but with Behaviors not work.
In my current solution I attach behavior in code.
Any idea?

Answer 1

you can create the generic Behavior inside your view model then inject it to your control using attached properties.
public class ViewModel
{
public Behavior MyBehavior
{
get
{
return new GenericBehavior<SomeType>();
}
}
}
public class AttachedBehaviors
{
public static Behavior GetBehavior(DependencyObject sender) => (Behavior)sender.GetValue(BehaviorProperty);
public static void SetBehavior(DependencyObject sender, Behavior value) => sender.SetValue(BehaviorProperty, value);
public static readonly DependencyProperty BehaviorProperty =
DependencyProperty.RegisterAttached("Behavior", typeof(Behavior), typeof(AttachedBehaviors),
new PropertyMetadata(null, new PropertyChangedCallback(BehaviorChanged)));
private static void BehaviorChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
if (sender is FrameworkElement elem)
{
if (e.NewValue is Behavior behavior)
{
BehaviorCollection Behaviors = Interaction.GetBehaviors(elem);
Behaviors.Add(behavior);
}
}
}
}
public class GenericBehavior<T> : Behavior<DataGrid> where T : class
{
public T TestValue { get; set; }
protected override void OnAttached()
{
}
}
now you can use it like this
<DataGrid local:AttachedBehaviors.Behavior="{Binding MyBehavior}" >
</DataGrid>
PS: you just need to install Microsoft.Xaml.Behaviors.Wpf NuGet package.