Skip to main content

Binding Enum with DescriptionAttribute in WPF

Binding an enumeration to a ComboBox can be done in several ways. In most cases you don't want to display the value itself, but a more user friendly description. One common approach is to use the DescriptionAttribute on the Enum values to supply a description for each value. This is all possible in a very MVVM friendly way.

First step is to add the DescriptionAttribute to the values of the enumeration.

public enum MyValues
{
    [Description("First value")]
    First,

    [Description("Second value")]
    Second
}

To retrieve the description from the enum we use a simple extension method. This method returns the value of the DescriptionAttribute if it exists, otherwise the string representation of the enum value is returned.

public static string GetDescription(this Enum value)
{
    var fieldInfo = value.GetType().GetField(value.ToString());
    var attribute = fieldInfo.GetCustomAttributes(typeof(DescriptionAttribute), false).FirstOrDefault() as DescriptionAttribute;

    return attribute != null ? attribute.Description : value.ToString();
}

With this extension method it is really easy to write a generic enum description converter to use where ever an enum value is presented to the user. But the more interesting case is where we want to present the enumeration in a ComboBox or a similar control. To accomplish this you can use a MarkupExtension. (Please note that this code is stripped from all type validation and such to be easier to read.)

public class EnumExtension : MarkupExtension
{
    private readonly Type _enumType;

    public EnumExtension(Type enumType)
    {
        _enumType = enumType;
    }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        return (from object enumValue in Enum.GetValues(_enumType)
                select new EnumMember {Value = enumValue, Description = ((Enum)enumValue).GetDescription()}).ToArray();
    }

    public class EnumMember
    {
        public string Description { get; set; }
        public object Value { get; set; }
    }
}

The DescriptionAttribute together with these extensions gives us a really neat way of populating the values of an enum into a ComboBox.

<ComboBox SelectedValue="{Binding MyValue}"
          ItemsSource="{Binding Source={my:EnumExtension {x:Type MyValues}}}"
          DisplayMemberPath="Description" SelectedValuePath="Value" />

Comments

Popular posts from this blog

The Cornball goes to Brunch with Chaplin

Lately I've been working pretty hard on different projects but not really stumbling upon anything blogworthy. The most recent project is quite interesting though, a single page, touch friendly, web application using the latest and greatest technologies. We've ended up with using Brunch with Chaplin, which is a very neat way of setting up a Backbone based single page web project with Brunch and Chaplin.

Aside from this, I have my own little project that has lived on for almost 15 years already, The Cornball. From being a plain Windows application written i C an Win32 API, it has been ported to .NET using WPF, and is currently a Silverlight application hosted on Windows Azure.

I could not find a better time to reanimate this project and create a new web based version, touch friendly, super optimized, awesome in any way. So I did... So please follow my journey at Github. It's going to take a while, I assure you, but I already have some ground work done.

Meanwhile, check out …

Binding a HTML-formatted string to a WPF WebBrowser control

Sometimes there is a need to display a HTML formatted string in a WPF application. There are a couple of ways to do this, but the most stright forward is to use a WebBrowser control and the NavigateToString method.

This approach has one big flaw, you cannot use binding to a string out of the box, but I found a great solution through Stack Overflow which adds a bindable property to the  WebBrowser control using  NavigateToString.

The following class is all that is needed to add that behavior. A new depencency property named Html is introduced to the  WebBrowser and the proper change action is performed in the OnHtmlChanged method.

public class BrowserBehavior { public static readonly DependencyProperty HtmlProperty = DependencyProperty.RegisterAttached( "Html", typeof(string), typeof(BrowserBehavior), new FrameworkPropertyMetadata(OnHtmlChanged)); [AttachedPropertyBrowsableForType(typeof(WebBrowser))] public static string GetHtml(WebBrowser browser) { …

Using Bootstrap Tooltip to show Parsley validation errors

I'm currently working on a web application using a variety of different frameworks, such as Backbone for the back-end, Bootstrap for the front-end and Parsley for client side form validation. Parsley is a really powerful validation toolkit, but it takes some tweaking to make it blend with the Bootstrap front-end. Fortunately this is a one time fix, which can be re-used all over our project.

Since there will be some custom options in our Parsley object, we can't use the default parsley-validate attribute on the form. Instead we have to initialize the validation with the jQuery syntax:

$('#my-form').parsley(parsleyOptions);
The options are were the magic happens, and in our case we have a global options object that our forms use to get the same experience all over the application. Here's what it looks like:

var parsleyOptions = {  // Sets success and error class to Bootstrap class names  successClass: 'has-success',  errorClass: 'has-error',  // Bo…