Pass Data to Data Template Selector

Question

How do you guys pass the data (parameter) to DataTemplate Selector?

The only one that I can think of is to use an attached property in DataTemplate Selector?

Example:

public class DisableWeekendsSelection : DataTemplateSelector
    {
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2211:NonConstantFieldsShouldNotBeVisible", Justification = "DependencyProperty")]
        public static readonly DependencyProperty Parameter =
           DependencyProperty.RegisterAttached("Parameter", typeof(ObservableCollection<Date>), typeof(DisableWeekendsSelection),
           new FrameworkPropertyMetadata(null,
               FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));

        public static ObservableCollection<Date> GetParameter(DependencyObject dp)
        {
            return dp.GetValue(Parameter) as ObservableCollection<Date>;            
        }

        public static void SetParameter(DependencyObject dp, ObservableCollection<Date> value)
        {            
            dp.SetValue(Parameter, value);
        }

        public override DataTemplate SelectTemplate(object item, DependencyObject container)
        {

The problem with this approach is that I'm not able to get the value of Parameter in SelectTemplate method.

Any suggestion would be appreciated. Thanks in advance.

Answer 1

This is quite a bit easier. In the handler:

SelectTemplate(object item, DependencyObject container)

The container is in the logical tree. You can recurse up the tree to get to your UserControl and you then have access to that controls properties and DataContext. Like this:

public override DataTemplate SelectTemplate(object item, DependencyObject container)
{
    var _Container = Library.TreeHelper.TryFindParent<MyUserControl>(container);

Here's the helper method: http://www.hardcodet.net/2009/06/finding-elements-in-wpf-tree-both-ways

Answer 2

The usual solution is to use the properties of the item parameter to get the needed info to choose the right template.

If you have a ViewModel, it can include the necessary data.

Answer 3

Workarounds

1. Use the attached property and private static variable

2. Walk the Visual Tree doc.OfParentType<>