Multiple Media Picker returns list of IPublishedElement

Note: Umbraco HQ has marked this as breaking. Some more info is available below:

Unfortunately fixing this issue led to an unintended breaking change, as you can read below, you will run into this is you are currently querying items picked in a media picker in a strongly typed way, like:

@if (post.PreviewImage != null)
{
     <img src="@post.PreviewImage.GetCropUrl("Blog Preview")" alt="@post.PreviewImage.AltDescription">
}

altDescription in this case is a property on you media type, it could also be the default umbracoWidth property for example.

To fix this, you can update your view in a few different ways:

1. Use the returned IPublishedContent directly and get the Value for the property like you are used to from other pickers:

@if (post.PreviewImage != null)
{
     <img src="@post.PreviewImage.GetCropUrl("Blog Preview")" alt="@post.PreviewImage.Value("altDescription")">
}

1. If you enjoy working with strongly typed objects you can cast the item you’re working with to the type you know it should be, for example:

@if (post.PreviewImage is Image previewImage)
{
     <img src="@previewImage.GetCropUrl("Blog Preview")" alt="@previewImage.AltDescription">
}

1. For you ModelsBuilder lovers, Stéphane has described some additional options here: https://www.zpqrtbnk.net/posts/umbraco-8-1-4-breaking-models-builder/

The original issue description follows:

---

Hi

When creating a Media Picker data type and setting both “Pick multiple items” and “Pick only images” to true, then it consistently returns IEnumerable<IPublishedElement> instead of IEnumerable<IPublishedContent>.

So if we do a similar setup, like the one in the documentation (https://our.umbraco.com/documentation/Getting-Started/Backoffice/Property-Editors/Built-in-Property-Editors/Media-Picker/) and try to retrieve the value as mentioned in the documentation too, then it will throw an null error.

@{
    var typedMultiMediaPicker = Model.Value<IEnumerable<IPublishedContent>>("sliders");
    foreach (var item in typedMultiMediaPicker)
    {
        <img src="@item.Url" style="width:200px"/>
    }
}

It works just fine in all other combinations, except when the two checkboxes are both set to true.

I have experienced this bug on every Umbraco 8 versions so far.

[ronaldbarendse]

The following custom PVC makes sure the returned type is set back to Image or IEnumerable<Image> (if ‘Pick only images’ is checked), but now only contains items that actually inherit from this type (as opposed to throwing exceptions):

using System;
using System.Collections.Generic;
using Umbraco.Core;
using Umbraco.Core.Models.PublishedContent;
using Umbraco.Core.PropertyEditors;
using Umbraco.Web.PropertyEditors;
using Umbraco.Web.PropertyEditors.ValueConverters;
using Umbraco.Web.PublishedCache;

public class CustomMediaPickerValueConverter : MediaPickerValueConverter
{
	private const string ImageTypeAlias = Constants.Conventions.MediaTypes.Image;
	private readonly IPublishedModelFactory _publishedModelFactory;

	public CustomMediaPickerValueConverter(IPublishedSnapshotAccessor publishedSnapshotAccessor, IPublishedModelFactory publishedModelFactory)
		: base(publishedSnapshotAccessor, publishedModelFactory)
	{
		_publishedModelFactory = publishedModelFactory;
	}

	public override Type GetPropertyValueType(IPublishedPropertyType propertyType)
	{
		var baseType = base.GetPropertyValueType(propertyType);
		if (IsOnlyImagesDataType(propertyType.DataType))
		{
			return (baseType == typeof(IEnumerable<IPublishedContent>))
				? typeof(IEnumerable<>).MakeGenericType(ModelType.For(ImageTypeAlias))
				: ModelType.For(ImageTypeAlias);
		}

		return baseType;
	}

	public override object ConvertIntermediateToObject(IPublishedElement owner, IPublishedPropertyType propertyType, PropertyCacheLevel cacheLevel, object source, bool preview)
	{
		var baseSource = base.ConvertIntermediateToObject(owner, propertyType, cacheLevel, source, preview);
		if (IsOnlyImagesDataType(propertyType.DataType))
		{
			var imageType = _publishedModelFactory.MapModelType(ModelType.For(ImageTypeAlias));

			if (baseSource is IEnumerable<IPublishedContent> mediaItems)
			{
				var images = _publishedModelFactory.CreateModelList(ImageTypeAlias);

				foreach (var mediaItem in mediaItems)
				{
					if (mediaItem.GetType().Inherits(imageType))
					{
						images.Add(mediaItem);
					}
				}

				return images;
			}
			else if (baseSource != null)
			{
				return baseSource != null && baseSource.GetType().Inherits(imageType) ? baseSource : null;
			}
		}

		return baseSource;
	}

	private bool IsOnlyImagesDataType(PublishedDataType dataType)
	{
		var config = ConfigurationEditor.ConfigurationAs<MediaPickerConfiguration>(dataType.Configuration);
		return config.OnlyImages;
	}
}

If this class is added to a project, it will automatically be registered and replace the default PVC. This could be a lot cleaner if the default MediaPickerValueConverter is updated with my comments from https://github.com/umbraco/Umbraco-CMS/pull/6034#issuecomment-528327808, but it works and keeps duplicated code to a minimum.

[ronaldbarendse]

@nul800sebastiaan Make sure to update option 2, as it currently can throw a NullReferenceException if the preview image isn’t of type Image. @NikRimington’s https://github.com/umbraco/Umbraco-CMS/pull/6034#issuecomment-527425298 might also be updated. Better provide correct working examples, especially for the people who like to copy-paste 😉

Using pattern-matching, this can be written as:

@if (post.PreviewImage is Image previewImage)
{
     <img src="@previewImage.GetCropUrl("Blog Preview")" alt="@previewImage.AltDescription">
}