I am trying to create a custom WPF control that has multiple UI elements to be displayed in different situations at different times, so they cannot be sensibly created in the same visual tree. I created dependency properties for each element, of type UIElement. This worked well.
When it came to styling control, it didn’t work so well. Although I can define a style for the control that sets my custom properties, the style is only instantiated once. So if multiple instances of my custom control use the same style, only the last one to be defined gets the visual tree. I understand that this is because the style sets the UIElement directly rather than using a template, and it is the template infrastructure that makes multiple instances of the tree defined within it (see https://stackoverflow.com/a/8702180/1453269)
My question is, how can I define a control that takes multiple templates in such a way that they will be applied? I have tried creating dependency objects of type DataTemplate. If I use a ContentPresenter to display the template, it just displays the type name of DataTemplate as text. I want it to apply the template values to my first dependency properties in a manner consistent with the rest of WPF. I had assumed there is a way to leverage the templating infrastructure in WPF, but I can’t find how to do that.
The key is the LoadContent method on FrameworkTemplate (from which DataTemplate derives). This method creates a copy of the template’s content.
So to implement multiple templates, I created a Content and a Template pair of dependency properties for each templated UI property that I wanted. I registered for change notifications on the XXXTemplate dependency properties. The event handlers called into a method that set the matching XXXContent dependency property to the return value of LoadContent called on the new template value.
In my control template for the containing object, I could then use a ContentPresenter bound to the XXXContent property of the desired UIElement.