Avalonia EnumDescriptionConverter Sample - Display Enums in ComboBox

README.md

C# XAML (AXAML) ComboBox with Enum Descriptions

This example of how to bind a ComboBox to an enumeration, providing human-readable text in the collection. Please note, this makes use of the Prism Library's SetParameter(...) method which also exist in the CommunityToolkit.

This can be used in XAML-based frameworks such as WPF, Avalonia, .NET MAUI, UNO, etc.

EnumDescriptionConverter.cs

using System;
using System.ComponentModel;
using System.Globalization;
using System.Reflection;
using Avalonia.Data.Converters;

namespace Diagnostics.Converters;

public class EnumDescriptionConverter : IValueConverter
{
  public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
  {
    if (value is Enum enumValue)
    {
      FieldInfo? fieldInfo = enumValue.GetType().GetField(enumValue.ToString());
      if (fieldInfo != null)
      {
        var attributes = (DescriptionAttribute[])fieldInfo.GetCustomAttributes(typeof(DescriptionAttribute), false);
        ////if (attributes.Length > 0 && !string.IsNullOrEmpty(attributes[0].Description))
        ////  return attributes[0].Description;

        if (attributes.Length > 0)
        {
          foreach (var attr in attributes)
            if (attr is DescriptionAttribute descAttr)
              return descAttr.Description;
        }
      }
    }

    return value?.ToString();
  }

  public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
  {
    return string.Empty;

    // Optional:
    // throw new NotImplementedException();
  }
}

SampleView.axaml

<UserControl xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:local="clr-namespace:Diagnostics.Converters;assembly=Diagnostics"
             ...>
  <UserControl.Resources>
    <ResourceDictionary>
      <local:EnumDescriptionConverter x:Key="EnumConverter" />
    </ResourceDictionary>
  </UserControl.Resources>
  
  <StackPanel>
    <ComboBox ItemsSource="{Binding ZoneTypes}" SelectedItem="{Binding ZoneTypeSelected}">
      <ComboBox.ItemTemplate>
        <DataTemplate>
          <TextBlock Text="{Binding Converter={StaticResource EnumConverter}}" />
        </DataTemplate>
      </ComboBox.ItemTemplate>
    </ComboBox>
  </StackPanel>
</UserControl>

SampleViewModel.cs

using Prism.Commands;
using Prism.Mvvm;

public class SampleViewModel : BindableBase
{
  private ZoneType _zoneTypeSelected;
  
  public ZoneType ZoneTypeSelected { get => _zoneTypeSelected; set => SetProperty(ref _zoneTypeSelected, value); }

  public IEnumerable<ZoneType> ZoneTypes => Enum.GetValues<ZoneType>().Cast<ZoneType>();
  //// public IEnumerable<ZoneType> ZoneTypes => Enum.GetValues(typeof(ZoneType)).Cast<ZoneType>();
}

ZoneType.cs

using System.ComponentModel;

namespace Diagnostics.Models;

/// <summary>Zone Types.</summary>
public enum ZoneType
{
  /// <summary>Unspecified.</summary>
  [Description("N/A")]
  Unknown = 0,

  /// <summary>Upper zone.</summary>
  [Description("Upper Zone")]
  Zone1,

  /// <summary>Middle zone.</summary>
  [Description("Middle Zone")]
  Zone2,

  /// <summary>Bottom zone.</summary>
  [Description("Bottom Zone")]
  Zone3,
}

zzzOthersFromInternet.z

# Other Methods from the Internet

## Avalonia Discussion Approach

// Alternative approaches below
// https://github.com/AvaloniaUI/Avalonia/discussions/8175

## AI Slop

The following was generated by Google's AI slop. It does not work, and is here as an example of how not to do things.

```cs
// Throws error when NULL
public class EnumDescriptionConverter : IValueConverter
{
  public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
  {
    Enum myEnum = (Enum)value;
    string description = GetEnumDescription(myEnum);
    return description;
  }

  public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
  {
    return string.Empty;
  }

  private string GetEnumDescription(Enum enumObj)
  {
    FieldInfo fieldInfo = enumObj.GetType().GetField(enumObj.ToString());
    object[] attribArray = fieldInfo.GetCustomAttributes(false);

    if (attribArray.Length == 0)
      return enumObj.ToString();
    else
    {
      DescriptionAttribute attrib = null;

      foreach (var att in attribArray)
      {
        if (att is DescriptionAttribute)
          attrib = att as DescriptionAttribute;
      }

      if (attrib != null)
        return attrib.Description;

      return enumObj.ToString();
    }
  }
}
```

## Overkill EnumDescriptionConverter

```cs
public class EnumDescriptionConverter : IValueConverter
{
  public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
  {
    if (value.GetType().IsEnum)
      return ((Enum)value).ToDescription();

    throw new ArgumentException("Convert:Value must be an enum.");
  }

  public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
  {
    if (value is EnumDescription enumDescription)
      return enumDescription.Value;

    throw new ArgumentException("ConvertBack:EnumDescription must be an enum.");
  }
}

public record EnumDescription
{
  public object Value { get; set; }

  public string Description { get; set; }

  public string Help { get; set; }

  public override string ToString()
  {
    return Description;
  }
}

public static class EnumUtils
{
  public static IEnumerable<EnumDescription> ToDescriptions(Type t)
  {
    if (!t.IsEnum)
      throw new ArgumentException($"{nameof(t)} must be an enum type");

    return Enum.GetValues(t).Cast<Enum>().Select(ToDescription).ToList();
  }

  public static EnumDescription ToDescription(this Enum value)
  {
    string description;
    string help = null;

    var attributes = value.GetType().GetField(value.ToString()).GetCustomAttributes(typeof(DescriptionAttribute), false);
    if (attributes.Any())
    {
      description = (attributes.First() as DescriptionAttribute)?.Description;
    }
    else
    {
      TextInfo ti = CultureInfo.CurrentCulture.TextInfo;
      description = ti.ToTitleCase(ti.ToLower(value.ToString().Replace("_", " ")));
    }

    if (description.IndexOf(';') is var index && index != -1)
    {
      help = description.Substring(index + 1);
      description = description.Substring(0, index);
    }

    return new EnumDescription() { Value = value, Description = description, Help = help };
  }

  public static string GetStringValue(Enum value)
  {
    string output = null;
    Type type = value.GetType();
    FieldInfo fi = type.GetField(value.ToString());

    if (fi.GetCustomAttributes(typeof(StringValue),
            false) is StringValue[] { Length: > 0 } attrs)
    {
      output = attrs[0].Value;
    }

    return output;
  }

  public static T? Parse<T>(string input) where T : struct
  {
    if (!typeof(T).IsEnum)
    {
      throw new ArgumentException("Generic Type 'T' must be an Enum.");
    }

    if (string.IsNullOrEmpty(input))
      return null;

    if (Enum.GetNames(typeof(T)).Any(
            e => e.Trim().ToUpperInvariant() == input.Trim().ToUpperInvariant()))
    {
      return (T)Enum.Parse(typeof(T), input, true);
    }

    return null;
  }
}
```