Assets and image display

In a standard Xamarin project, you must duplicate, rename, and manually add your assets to each target project (UWP, iOS, Android).

Xamarin: Working with Images

We still recommend using the above technique for platform-specific icons and splash screens in Uno.UI projects.

For most other assets, Uno.UI uses custom build tasks to lets you include assets once in shared projects and automatically use them on all platforms. The rest of this document will cover those particular features.

Supported asset types

At the moment, only the following image file types are supported:

.bmp (Win BMP) .gif‡ .heic (Apple) .jpg & .jpeg (JFIF) .png .webp .pdf .svg
Windows UWP ✔️ ✔️ ✔️ ✔️ ✔️ ✔️
Android 10 ✔️ ✔️‡ ✔️ ✔️ ✔️ ✔️ ✔️ ✔️
iOS 13 ✔️ ✔️‡ ✔️ ✔️ ✔️
macOS ✔️ ✔️‡ ✔️ ✔️ ✔️ ✔️
Wasm† ✔️ ✔️‡ ❌† ✔️ ✔️ ❌† ❌† ✔️
Skia WPF ✔️ ✔️‡ ✔️ ✔️ ✔️
  • † Actual Wasm image format support is browser dependent. For example, .webp is not working on Safari on macOS, but works on Chromium-based browsers. Checkmarks (✔️) indicates a format that can safely expected to work on all browsers able to run Wasm applications.
  • Gif animation support:
    • Play/Pause not implemented in Uno yet
    • Always animated on Wasm
    • Not animated on other Uno platforms

Adding an asset to your project

This is just like adding an asset to any UWP project. Just make sure to add the asset to a shared project to make it available to all platforms.

  1. Add the image file to the Assets directory of a shared project.
  2. Set the build action to Content.

Qualify an asset

On UWP, you can use qualifiers to load different assets depending on scale, language, etc.

Microsoft: Tailor your resources for language, scale, high contrast, and other qualifiers

You can do the same thing with Uno.UI, although only a subset of those qualifiers are supported.

Scale

Not all scales are supported on all platforms:

Scale UWP iOS Android
100 scale-100 @1x mdpi
125 scale-125 N/A N/A
150 scale-150 N/A hdpi
200 scale-200 @2x xhdpi
300 scale-300 @3x xxhdpi
400 scale-400 N/A xxxhdpi

We recommend including assets for each of these scales: 100, 150, 200, 300 and 400. Only compatible scales will be included to each platform.

Note: In the Android head project (via the csproj), you can set the UseHighDPIResources property to False in debug. In those cases, only assets with scale 100 (mdpi) and scale 150 (hdpi) will be included. This reduces deployment time when debugging as fewer assets are processed and transferred to the device or simulator.

Examples

\Assets\Images\logo.scale-100.png
\Assets\Images\logo.scale-200.png
\Assets\Images\logo.scale-400.png

\Assets\Images\scale-100\logo.png
\Assets\Images\scale-200\logo.png
\Assets\Images\scale-400\logo.png

Language

Use it as you would on UWP, but keep in mind that some language/region combinations might not work on all platforms.

The following languages have been verified to work on all platforms:

  • en
  • en-US
  • en-CA
  • fr
  • fr-FR
  • fr-CA
  • es

Examples

\Assets\Images\en\logo.png
\Assets\Images\fr\logo.png
\Assets\Images\es\logo.png

\Assets\Images\logo.language-en.png
\Assets\Images\logo.language-fr.png
\Assets\Images\logo.language-es.png

Dark theme support

Supported on Android only

A theme qualifier can be specified for the image loader to use an asset based on the current app theme.

Examples

/Assets/theme-light/ThemeTestImage.png
/Assets/theme-dark/ThemeTestImage.png

Custom (platform)

Sometimes, you might want to use a different asset depending on the platform. Because there is no platform qualifier on UWP, we had to use the custom qualifier.

Platform Qualifier value
UWP uwp
iOS ios
Android android

Because the custom qualifier doesn't have any special meaning on UWP, we have to interpret its value manually.

On iOS and Android, Uno.UI's RetargetAssets task automatically interprets these values and excludes unsupported platforms.

On UWP, you must add the following code to your App.xaml.cs constructor:

#if WINDOWS_UWP
	Windows.ApplicationModel.Resources.Core.ResourceContext.SetGlobalQualifierValue("custom", "uwp");
#endif

Examples

\Assets\Images\custom-uwp\logo.png
\Assets\Images\custom-ios\logo.png
\Assets\Images\custom-android\logo.png

\Assets\Images\logo.custom-uwp.png
\Assets\Images\logo.custom-ios.png
\Assets\Images\logo.custom-android.png

Android: setting a custom image handler

On Android, to handle the loading of images from a remote url, the Image control has to be provided a ImageSource.DefaultImageLoader such as the Android Universal Image Loader.

This package is installed by default when using the Uno Cross-Platform solution templates. If not using the solution template, you can install the nventive.UniversalImageLoader NuGet package and call the following code from your application's App constructor:

private void ConfigureUniversalImageLoader()
{
	// Create global configuration and initialize ImageLoader with this config
	ImageLoaderConfiguration config = new ImageLoaderConfiguration
		.Builder(Context)
		.Build();

	ImageLoader.Instance.Init(config);

	ImageSource.DefaultImageLoader = ImageLoader.Instance.LoadImageAsync;
}

iOS: referencing bundle images

On iOS, bundle images can be selected using "bundle://" (e.g. bundle:///SplashScreen). When selecting the bundle resource, do not include the zoom factor, nor the file extension.