Image.asset constructor

Implementation

//
// TODO(ianh): Implement the following (see ../services/image_resolution.dart):
// ///
// /// * If [width] and [height] are both specified, and [scale] is not, then
// ///   size-aware asset resolution will be attempted also, with the given
// ///   dimensions interpreted as logical pixels.
// ///
// /// * If the images have platform, locale, or directionality variants, the
// ///   current platform, locale, and directionality are taken into account
// ///   during asset resolution as well.
///
/// The [name] and [repeat] arguments must not be null.
///
/// Either the [width] and [height] arguments should be specified, or the
/// widget should be placed in a context that sets tight layout constraints.
/// Otherwise, the image dimensions will change as the image is loaded, which
/// will result in ugly layout changes.
///
/// Use [filterQuality] to change the quality when scaling an image.
/// Use the [FilterQuality.low] quality setting to scale the image,
/// which corresponds to bilinear interpolation, rather than the default
/// [FilterQuality.none] which corresponds to nearest-neighbor.
///
/// {@tool sample}
///
/// Suppose that the project's `pubspec.yaml` file contains the following:
///
/// ```yaml
/// flutter:
///   assets:
///     - images/cat.png
///     - images/2x/cat.png
///     - images/3.5x/cat.png
/// ```
/// {@end-tool}
///
/// On a screen with a device pixel ratio of 2.0, the following widget would
/// render the `images/2x/cat.png` file:
///
/// ```dart
/// Image.asset('images/cat.png')
/// ```
///
/// This corresponds to the file that is in the project's `images/2x/`
/// directory with the name `cat.png` (the paths are relative to the
/// `pubspec.yaml` file).
///
/// On a device with a 4.0 device pixel ratio, the `images/3.5x/cat.png` asset
/// would be used. On a device with a 1.0 device pixel ratio, the
/// `images/cat.png` resource would be used.
///
/// The `images/cat.png` image can be omitted from disk (though it must still
/// be present in the manifest). If it is omitted, then on a device with a 1.0
/// device pixel ratio, the `images/2x/cat.png` image would be used instead.
///
///
/// ## Assets in packages
///
/// To create the widget with an asset from a package, the [package] argument
/// must be provided. For instance, suppose a package called `my_icons` has
/// `icons/heart.png` .
///
/// {@tool sample}
/// Then to display the image, use:
///
/// ```dart
/// Image.asset('icons/heart.png', package: 'my_icons')
/// ```
/// {@end-tool}
///
/// Assets used by the package itself should also be displayed 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:
///
/// ```yaml
///  assets:
///    - packages/fancy_backgrounds/backgrounds/background1.png
/// ```
///
/// The `lib/` is implied, so it should not be included in the asset path.
///
///
/// See also:
///
///  * [AssetImage], which is used to implement the behavior when the scale is
///    omitted.
///  * [ExactAssetImage], which is used to implement the behavior when the
///    scale is present.
///  * <https://flutter.io/assets-and-images/>, an introduction to assets in
///    Flutter.
Image.asset(String name, {
  Key key,
  AssetBundle bundle,
  this.semanticLabel,
  this.excludeFromSemantics = false,
  double scale,
  this.width,
  this.height,
  this.color,
  this.colorBlendMode,
  this.fit,
  this.alignment = Alignment.center,
  this.repeat = ImageRepeat.noRepeat,
  this.centerSlice,
  this.matchTextDirection = false,
  this.gaplessPlayback = false,
  String package,
  this.filterQuality = FilterQuality.low,
}) : image = scale != null
       ? ExactAssetImage(name, bundle: bundle, scale: scale, package: package)
       : AssetImage(name, bundle: bundle, package: package),
     assert(alignment != null),
     assert(repeat != null),
     assert(matchTextDirection != null),
     super(key: key);