IMauiContext not found when trying to get bitmap from FontImageSource

Question

Hi.
I have next error

System.InvalidOperationException: IMauiContext not found.
[mono-rt]    at Microsoft.Maui.Controls.ViewExtensions.RequireMauiContext(Element element, Boolean fallbackToAppMauiContext) in D:\a\_work\1\s\src\Controls\src\Core\ViewExtensions.cs:line 200
[mono-rt]    at Microsoft.Maui.Controls.ViewExtensions.RequireFontManager(Element element, Boolean fallbackToAppMauiContext) in D:\a\_work\1\s\src\Controls\src\Core\ViewExtensions.cs:line 217
[mono-rt]    at Microsoft.Maui.Controls.Compatibility.Platform.Android.FontImageSourceHandler.LoadImageAsync(ImageSource imagesource, Context context, CancellationToken cancelationToken) in D:\a\_work\1\s\src\Compatibility\Core\src\Android\Renderers\FontImageSourceHandler.cs:line 36

My code:

public static IImageSourceHandler GetHandler(this ImageSource imageSource)
        {
            if (imageSource is FileImageSource)
                return new FileImageSourceHandler();
            if (imageSource is StreamImageSource)
                return new StreamImagesourceHandler();
            if (imageSource is UriImageSource)
                return new ImageLoaderSourceHandler();
            if (imageSource is FontImageSource)
                return new FontImageSourceHandler();
            return null;
        }

        public static Task<Bitmap> ToBitmap(this ImageSource imageSource, CancellationToken cancellationToken = default)
        {
            if (imageSource == null)
                return null;
            IImageSourceHandler handler = imageSource.GetHandler();
            return handler.LoadImageAsync(imageSource, MainActivity.Instance, cancellationToken);
        }

        public static async Task<BitmapDrawable> ToBitmapDrawable(this ImageSource imageSource, CancellationToken cancellationToken = default)
        {
            if (imageSource == null)
                return null;
            Bitmap bitmap = await imageSource.ToBitmap(cancellationToken);
            return new BitmapDrawable(MainActivity.Instance.Resources, bitmap);
        }

I have a custom Entry with image and want to use it:

<controls:MaterialEntry Type="Outlined" Placeholder="Підрозділ">
                    <controls:MaterialEntry.LeadingImageSource>
                        <FontImageSource FontFamily="MaterialOutline"
                                         Glyph="{Static icons:MaterialOutline.Store}"
                                         Color="{DynamicResource OnSurfaceVariantColor}"/>
                    </controls:MaterialEntry.LeadingImageSource>
                </controls:MaterialEntry>

In handler:

public static async void MapLeadingImage(IMaterialEntryHandler handler, IMaterialContainer entry) =>
            handler.PlatformView.StartIconDrawable = await entry.LeadingImageSource.ToBitmapDrawable(new CancellationToken());

Full code here
How can I get bitmap from ImageSource? Thanks.

Answer 1

Hello,

I check your sample, and I found you set null if the imagesource is null in ToBitmapDrawable method, try to set it a default instance, refer to the following code:

 public static async Task<BitmapDrawable> ToBitmapDrawable( this ImageSource imageSource, CancellationToken cancellationToken = default)  
        {  
            if (imageSource == null)  
                return new BitmapDrawable();  
            Bitmap bitmap = await imageSource.ToBitmap(cancellationToken);  
            return new BitmapDrawable(MainActivity.Instance.Resources, bitmap);  
        }  

And try to set your LeadingImageSourceProperty as a BindableProperty, add the following code into your MaterialEntry class:

 public static readonly BindableProperty LeadingImageSourceProperty =  
BindableProperty.Create(nameof(IMaterialEntry.LeadingImageSource), typeof(ImageSource), typeof(IMaterialEntry));  

Best Regards,
Wenyan Zhang

---

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Answer 2

Surfing maui sources I have found worth solution.

public static async Task<Drawable> GetDrawable(this ImageSource imageSource, IElementHandler handler)  
        {  
            IImageSourceServiceProvider imageSourceServiceProvider = handler.GetRequiredService<IImageSourceServiceProvider>();  
            IImageSourceService service = imageSourceServiceProvider.GetImageSourceService(imageSource);  
            IImageSourceServiceResult<PlatformImage> result = await service.GetDrawableAsync(imageSource, handler.MauiContext.Context);  
            return result.Value;  
        }  

This class is internal (as other methods I need from maui framework :) ), I just paste this to my code (maybe better to have this public?)

#if IOS || MACCATALYST  
using PlatformImage = UIKit.UIImage;  
using PlatformView = UIKit.UIView;  
#elif ANDROID  
using PlatformImage = Android.Graphics.Drawables.Drawable;  
using PlatformView = Android.Views.View;  
#elif WINDOWS  
using PlatformImage = Microsoft.UI.Xaml.Media.ImageSource;  
using PlatformView = Microsoft.UI.Xaml.FrameworkElement;  
#elif TIZEN  
using PlatformImage = Tizen.UIExtensions.ElmSharp.Image;  
using PlatformView = ElmSharp.EvasObject;  
#elif NETSTANDARD || (NET6_0 && !IOS && !ANDROID && !TIZEN)  
using PlatformImage = System.Object;  
using PlatformView = System.Object;  
#endif  

public static class ElementHandlerExtensions  
    {  
        public static IServiceProvider GetServiceProvider(this IElementHandler handler)  
        {  
            var context = handler.MauiContext ??  
                throw new InvalidOperationException($"Unable to find the context. The {nameof(ElementHandler.MauiContext)} property should have been set by the host.");  
  
            var services = context?.Services ??  
                throw new InvalidOperationException($"Unable to find the service provider. The {nameof(ElementHandler.MauiContext)} property should have been set by the host.");  
  
            return services;  
        }  
  
        public static T GetRequiredService<T>(this IElementHandler handler)  
            where T : notnull  
        {  
            var services = handler.GetServiceProvider();  
  
            var service = services.GetRequiredService<T>();  
  
            return service;  
        }  
    }  

Also, this is more MAUI approach then creating handler for each type of ImageSource (Xamarin approach).