AssetImage class

Fetches an image from an AssetBundle, having determined the exact image to use based on the context.

Given a main asset and a set of variants, AssetImage chooses the most appropriate asset for the current context, based on the device pixel ratio and size given in the configuration passed to resolve.

To show a specific image from a bundle without any asset resolution, use an AssetBundleImageProvider.

Naming assets for matching with different pixel densities

Main assets are presumed to match a nominal pixel ratio of 1.0. To specify assets targeting different pixel ratios, place the variant assets in the application bundle under subdirectories named in the form "Nx", where N is the nominal device pixel ratio for that asset.

For example, suppose an application wants to use an icon named "heart.png". This icon has representations at 1.0 (the main icon), as well as 1.5 and 2.0 pixel ratios (variants). The asset bundle should then contain the following assets:

heart.png
1.5x/heart.png
2.0x/heart.png

On a device with a 1.0 device pixel ratio, the image chosen would be heart.png; on a device with a 1.3 device pixel ratio, the image chosen would be 1.5x/heart.png.

The directory level of the asset does not matter as long as the variants are at the equivalent level; that is, the following is also a valid bundle structure:

icons/heart.png
icons/1.5x/heart.png
icons/2.0x/heart.png

assets/icons/3.0x/heart.png would be a valid variant of assets/icons/heart.png.

Fetching assets

When fetching an image provided by the app itself, use the assetName argument to name the asset to choose. For instance, consider the structure above. First, the pubspec.yaml of the project should specify its assets in the flutter section:

flutter:
  assets:
    - icons/heart.png

Then, to fetch the image, use

AssetImage('icons/heart.png')

Assets in packages

To fetch an asset from a package, the package argument must be provided. For instance, suppose the structure above is inside a package called my_icons. Then to fetch the image, use:

AssetImage('icons/heart.png', package: 'my_icons')

Assets used by the package itself should also be fetched using the package argument as above.

If the desired asset is specified in the pubspec.yaml of the package, it is bundled automatically with the app. In particular, assets used by the package itself must be specified in its pubspec.yaml.

A package can also choose to have assets in its 'lib/' folder that are not specified in its pubspec.yaml. In this case for those images to be bundled, the app has to specify which ones to include. For instance a package named fancy_backgrounds could have:

lib/backgrounds/background1.png
lib/backgrounds/background2.png
lib/backgrounds/background3.png

To include, say the first image, the pubspec.yaml of the app should specify it in the assets section:

 assets:
   - packages/fancy_backgrounds/backgrounds/background1.png

The lib/ is implied, so it should not be included in the asset path.

See also:

• Image.asset for a shorthand of an Image widget backed by AssetImage when used without a scale.