Wpf: Passing Parameters To A ResourceDictionary

Question

Is there a way to pass parameters to a resource dictionary? I think that I can attach a code behind for the purpose of specifying event handlers, but unfortunately, I also need to access a reference to the parent control from the event handlers. The codebehind, I believe, can be attached by specifying an x:Class attribute for the resource dictionary in xaml, and then creating a class in the same folder, the filename for which is something like [resource dictionary name].xaml.cs.

The purpose is to seperate the code for four hierarchical data templates that I'm using in a single treeview control. The xaml for the treeview is getting a bit long and ugly to look at, so I was hoping to break it down into four resource dictionaries. Any thoughts are welcome!

Andrew

Answer 1

Resource dictionaries sound like a slightly peculiar way to do this. Resource dictionaries are all about sharing instances - they let you use a single instance of something (e.g. a style, a template, a brush, or whatever) from multiple places. They're not really a mechanism for dividing your UI up to simplify individual Xaml files.

The usual mechanism for splitting overly complicated Xaml files up into a few, more manageable smaller files is the user control. (Resource dictionary merging comes into play when you already have a resource dictionary, and it's got too big. But you wouldn't normally introduce a resource dictionary just to start splitting things up. On the contrary, resource dictionaries tend to encourage overly large Xaml files, which is why dictionary merging had to be invented in the first place!)

Most of the time, when I define a data template, I make it contain nothing but a single user control. And if that becomes more complex, I'd split that user control up into more user controls.

From your description, it sounds like your Xaml file has become large because you've got four large hierarchical data templates in there. If you took the body of each template and turned it into a user control, your four templates would now become very simple - something like this:

<HierarchicalDataTemplate x:Key="t1" ItemsSource="{Binding Path=Children}">
    <loc:TreeItemTypeOne />
</HierarchicalDataTemplate>

and you'd most likely no longer need to put those templates into separate files. But because the guts of each template is now in a user control, that gives you a place to put your codebehind.

You mention needing a reference to the parent control. That worries me - it makes it sound like you have too much code in your codebehind. But one thing at a time... You could solve that problem by defining a dependency property called ParentControl on your user control, and then put this in the template:

<loc:TreeItemTypeOne
    ParentControl="{Binding RelativeSource=
        {RelativeSource AncestorType=loc:ParentControlType}}" />

But frankly, as soon as I find myself in a position where I need this, I ask myself: how did I get myself into a position where that seemed necessary, and what can I do to fix that?

Answer 2

You know you can merge your Resource Dictionaries and then reference the DataTemplate within those dictionaries as needed within the TreeView.