Question

I’m writing a WPF User Control for my application, wrapping a ListBox and a few other items.

The ListBox has a new ItemTemplate that presents four pieces of information for each item in my list. I can hard code each of the four bindings to specific properties on my list items and they display fine.

However, I want my UserControl to be a bit more flexible.

On ListBox and ComboBox there is a property DisplayMemberPath (inherited from ItemsControl) that seems to “inject” the appropriate property binding into the standard ItemTemplate.

How do I achieve the same result with my user control?

I’d like to set up four new properties to allow configuration of the information displayed:

public string LabelDisplayPath { get; set; } 
public string MetricDisplayPath { get; set; }
public string TitleDisplayPath { get; set; }
public string SubtitleDisplayPath { get; set; }

Reviewing ItemsControl.DisplayMemberPath with Reflector seems to go down the rabbit hole, I haven’t been able to fathom how it works.

Also, if I’m completely off course – and there’s another, more “WPF” technique that I should be using instead, please point me in that direction.

Update

Here’s a clarification of what I’m trying to achieve.

The ListBox within my user control displays four pieces of information per item: Label, Title, Subtitle and Metric

In one place, I want to use this User control to display a list of issues. Each issue looks like this:

public class Issue {
    public string Code { get; set; }
    public string Description { get; set; }
    public string Priority { get; set; }
    public string Reporter { get; set; }
}

When displaying issues, I want to use the following mappings:

Code --> Label
Description --> Title
Reporter --> Subtitle
Priority --> Metric

Elsewhere in the same application, I have a list of Posts that I want to display using the same UserControl. Each Post looks like this:

public class Post {
    public DateTime PostedOn { get; set; }
    public string Title { get; set; }
    public string Teaser { get; set; }
    public int CommentCount { get; set; }
}

When displaying posts, I want to use the following mappings:

PostedOn --> Label
Title --> Title
Teaser --> Subtitle
CommentCount --> Metric

Given that Issues and Posts are quite different abstractions, I don’t want to force them to have the same properties, just to allow the UserControl to be used unchanged. Instead, I want to introduce a little configurability so that I can reuse my UserControl in both sites cleanly.

Answer 1

I’ve found the solution to my problem – it’s a bit more complicated than I’d like …

On any ItemsControl, when you set the DisplayMemberPath property, an instance of the internal class DisplayMemberTemplateSelector is assigned to the ItemTemplateSelector. In effect, this class generates a custom DataTemplate with an appropriate binding to suit the current configuration of DisplayMemberPath. A new instance of this class is created and used every time that DisplayMemberPath is changed.

To replicate this on my own Usercontrol, instead of modifying my existing data template on the fly as I had originally intended, I need to create my own template selector helper class and mimic the same approach as ItemsControl.