Contains/Exists in list converter?

[LeoJHarris]

Hi there,

Just opening up discussion for a converter that would take a list and check if an object is in the list. My user case for this is for my current app, I have a AuthenticationProfile enum, similar to the ConnectionProfile in Essentials, basically I am looking to check if a certain AuthenticationProfile exists in the list of user authentication profiles.

public enum AuthenticationProfile
    {
        /// <summary>
        /// Uses password as primary authentication
        /// </summary>
        Password = 0,

        /// <summary>
        /// Pincode was setup but not enabled
        /// </summary>
        PinCodeSetup = 1,

        /// <summary>
        /// Pin code was setup and enabled
        /// </summary>
        PinCodeEnabled = 2,

        /// <summary>
        /// TouchId enabled
        /// </summary>
        TouchId = 3,
    }

<DataTrigger
 Binding="{Binding AuthenticationProfiles, 
Converter={StaticResource ListContainsItemConverter}, ConverterParameter={x:Static types:AuthenticationProfile.Password}}"
TargetType="ContentView"
Value="true">

I can look into doing this at some point if we don't currently support something like this type of converter. It doesn't have to only apply to enum's.

[bijington]

We don't have an explicit 'is something in a list' converter however, you could achieve the same result using the EnumToBoolConverter as it allows for multiple values to be defined.

https://docs.microsoft.com/en-gb/dotnet/communitytoolkit/maui/converters/enum-to-bool-converter

Let me know if this helps

[LeoJHarris]

That's is definitely helpful and would probably do what I need, that being said I went ahead and created a converter that checks if something being an enum in my case is in a list. If it might be helpful I can look into adding this in the future as time permits.

[bijington]

I can certainly see value in checking if something is in a list. If the implementation doesn't specifically rely on it being an enum then it sounds good to me. To start with are you able to share the details of your implementation?

[LeoJHarris]

@bijington

I've only tried it with Enums but seems to work for that, I dont see why it wouldnt work on non enum types but would need to confirm/test

   public class ListContainsItemConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (IsList(value))
            {
                IList listToCheck = buildList(GetListType(value), ((IList)value).Cast<object>().ToList());

                return listToCheck.Contains(parameter);
            }
            return false;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }

        public Type GetListType(object listToCheck)
        {
            if (listToCheck == null)
            {
                throw new ArgumentNullException(nameof(listToCheck));
            }

            Type type = listToCheck.GetType();

            if (!type.IsGenericType || type.GetGenericTypeDefinition() != typeof(List<>))
            {
                throw new ArgumentException("Type must be List<>, but was " + type.FullName, nameof(listToCheck));
            }

            return type.GetGenericArguments()[0];
        }

        public bool IsList(object listToCheck)
        {
            if (listToCheck == null)
            {
                return false;
            }

            return listToCheck is IList &&
                   listToCheck.GetType().IsGenericType &&
                   listToCheck.GetType().GetGenericTypeDefinition().IsAssignableFrom(typeof(List<>));
        }

        private IList buildList(Type objType, IList<object> listOfItems)
        {
            Type listType = typeof(List<>).MakeGenericType(objType);
            IList listToCheck = (IList)Activator.CreateInstance(listType);

            foreach (object item in listOfItems)
            {
                _ = listToCheck.Add(item);
            }
            return listToCheck;
        }
    }

[bijington]

Thank you for sharing this

[CliffAgius]

Closed as answered as per the Community Stand-up discussion here: https://youtu.be/N9wMcBP4jtg?t=2889