WPF and binding ToolTip to a DisplayAttribute

In my view model, I have added DisplayAttributes to my properties, and would now like to bind the ToolTip property of my TextBox controls to the Description property of the DisplayAttribute.

I found this SO question which handles the reading of the description, but can't figure out how to populate the ToolTip using the calculated description.

This seems like a roundabout way to do this since WPF doesn't support this attribute and so you'll be entering the attributes into the view-model and the view-model will be looking them up. They could be in any internal format.

In any case, here is a demo of the problem as you've stated it. We add a Descriptions property to the class that the text boxes are bound to. That property is a dictionary that maps property names to descriptions, that is, attributes. In the static constructor for the view-model we look up all the attributes and populate the dictionary.

A small XAML file with two text boxes:

<Grid >
    <StackPanel>
        <TextBox Text="{Binding FirstName}" ToolTip="{Binding Descriptions[FirstName]}"/>
        <TextBox Text="{Binding LastName}" ToolTip="{Binding Descriptions[LastName]}"/>
    </StackPanel>
</Grid>

the code-behind:

        DataContext = new DisplayViewModel();

and a rudimentary view-model with two properties:

public class DisplayViewModel
{
    private static Dictionary<string, string> descriptions;

    static DisplayViewModel()
    {
        descriptions = new Dictionary<string,string>();
        foreach (var propertyName in PropertyNames)
        {
            var property = typeof(DisplayViewModel).GetProperty(propertyName);
            var displayAttributes = property.GetCustomAttributes(typeof(DisplayAttribute), true);
            var displayAttribute = displayAttributes.First() as DisplayAttribute;
            var description = displayAttribute.Name;
            descriptions.Add(propertyName, description);
        }
    }

    public DisplayViewModel()
    {
        FirstName = "Bill";
        LastName = "Smith";
    }

    public static IEnumerable<string> PropertyNames { get { return new[] { "FirstName", "LastName" }; } }

    [Display(Name = "First Name")]
    public string FirstName { get; set; }

    [Display(Name = "Last Name")]
    public string LastName { get; set; }

    public IDictionary<string, string> Descriptions { get { return descriptions; } }
}