Changing a datatemplate at runtime - wpf

Question

I need to wrap a datatemplate in a datatemplate that gets built at run time. The wrapped datatemplate is WPF element where as the wrapping template needs to be created in code.
Something like:
public DataTemplate GetTemplate(DataTemplate template)
{
string xaml = string.Format(#"
<DataTemplate>
<ContentControl Content=""{{Binding}}"">
<ContentControl.ContentTemplate>
{0}
</ContentControl.ContentTemplate>
</ContentControl>
</DataTemplate>", template);
return CreateTemplate(xaml);
}
Obviously my datatemplate is more complicated then the one I'm using above.
I dont know of anyway to take an existing xaml element and convert it to a string. It seems like I might be able to use FrameworkElementFactory but I see it is depricated, which leads me to think I'm missing something obvious.
EDITED ---
What I'm doing is creating a control that users will supply a datatemplate but I need to make changes to the the template. Maybe this example will make more sense...
public DataTemplate GetTemplate2()
{
// this template would be supplied by the user
// I'm creating it here as an example
string t = string.Format(#"
<DataTemplate>
<TextBlock Text=""{{Binding Value}}""/>
</DataTemplate>");
T = CreateTemplate(t);
string xaml = string.Format(#"
<DataTemplate>
<ContentControl Content=""{{Binding}}"">
<ContentControl.ContentTemplate>
{0}
</ContentControl.ContentTemplate>
</ContentControl>
</DataTemplate>", t);
return CreateTemplate(xaml);
}
This all works because I'm using the string template (e.g. t). However I need to figure out some way to do it with the actual DataTemplate (e.g. T). Unfortunately XamlWriter can't deal with the Binding.

Answer 1

You can create a DataTemplate selector. There you can add your logic to build your DataTemplate at runtime. Also you can create a dependencyProperty in your DataTemplate selector. Then bind it in your xaml to a DataTemplate stored in some backing model, and there do what ever ...
This link might be a good place to start

Answer 2

You can use XamlWriter (the analog to XamlReader) but it has limitations on what can be properly serialized. Things like event handlers and x:Names cause issues.
**UPDATE
Seeing the additional detail I think you should try reversing your approach. Rather than combining the templates using strings and then trying to turn that into the object you want, you can avoid all the weird parsing restrictions by just creating the user's template as a DataTemplate object and then building your own DataTemplate object around it. Your example code is also using 2 Value Paths, which is going to give you .Value.Value on the inner template Text so check to make sure on your real one that you're ending up with the Paths you want. Here's the basics of your example using the objects instead, with the paths updated to expect a String and display its length:
DataTemplate T = XamlReader.Parse(string.Format(#"
<DataTemplate xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation'>
<TextBlock Text=""{{Binding}}""/>
</DataTemplate>")) as DataTemplate;
FrameworkElementFactory controlFactory = new FrameworkElementFactory(typeof(ContentControl));
controlFactory.SetBinding(ContentControl.ContentProperty, new Binding("Length"));
controlFactory.SetValue(ContentControl.ContentTemplateProperty, T);
DataTemplate mainTemplate = new DataTemplate { VisualTree = controlFactory };