How can you programatically retrieve the DataTemplate used for a specific element in the UI hierarchy?

Question

We need to determine, in code, what template would automatically be applied to a bound element, given a specific data type and that element.

We are not looking for a DataTemplateSelector as that's used to tell the UI which template to use for a given object based on custom logic. We're instead asking the UI which template will it use for a given data type and UI element.

In other words, we're looking for whatever WPF would apply based on the templates defined in the resources section of a window, which can be overridden by the resources of a control on that window, which can be overridden by explicitly setting the DataTemplate or providing a DataTemplateSelector directly on that element.

Also, we tried the default implementation of SelectTemplate but that returns null, so we can't go that route either.

A test would be to ask an element with no data templates or selectors defined anywhere in the UI 'How would you display this value?' and hopefully it will return a DataTemplate containing the definition for a TextBlock with the text property set to the ToString method on that object, which is what's displayed by default when nothing else is defined.

Answer 1

Thomas Levesque's untested solution didn't quite work for me but provided a great starting point. In our case the "container" argument is not always in the visual tree so first we walk up the logical tree until we find a visual. That, combined with MarqueIV's excellent suggestion, leads to a fairly simple solution.

The following code is working for me in production. Your mileage may vary. :)

public static DataTemplate FindTemplateForType(Type dataType, DependencyObject container)
{
    var frameworkElement = container as FrameworkElement;
    if (frameworkElement != null)
    {
        var key = new DataTemplateKey(dataType);
        var template = frameworkElement.TryFindResource(key) as DataTemplate;
        if (template != null)
            return template;
    }

    if (!(container is Visual || container is Visual3D))
    {
        container = FindClosestVisualParent(container);
        return FindTemplateForType(dataType, container);
    }
    else
    {
        var parent = VisualTreeHelper.GetParent(container);
        if (parent != null)
            return FindTemplateForType(dataType, parent);
        else
            return FindTemplateForType(dataType, Application.Current.Windows[0]);
    }
}

public static DependencyObject FindClosestVisualParent(DependencyObject initial)
{
    DependencyObject current = initial;
    bool found = false;

    while (!found)
    {
        if (current is Visual || current is Visual3D)
        {
            found = true;
        }
        else
        {
            current = LogicalTreeHelper.GetParent(current);
        }
    }

    return current;
}