packages/flutter/lib/src/widgets/fade_in_image.dart - mirrors/flutter - Git at Google

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 import 'dart:typed_data';

 import 'package:flutter/foundation.dart';
 import 'package:flutter/services.dart';

 import 'basic.dart';
 import 'framework.dart';
 import 'image.dart';
 import 'ticker_provider.dart';

 // Examples can assume:
 // Uint8List bytes;

 /// An image that shows a [placeholder] image while the target [image] is
 /// loading, then fades in the new image when it loads.
 ///
 /// Use this class to display long-loading images, such as [new NetworkImage],
 /// so that the image appears on screen with a graceful animation rather than
 /// abruptly pops onto the screen.
 ///
 /// If the [image] emits an [ImageInfo] synchronously, such as when the image
 /// has been loaded and cached, the [image] is displayed immediately and the
 /// [placeholder] is never displayed.
 ///
 /// [fadeOutDuration] and [fadeOutCurve] control the fade-out animation of the
 /// placeholder.
 ///
 /// [fadeInDuration] and [fadeInCurve] control the fade-in animation of the
 /// target [image].
 ///
 /// Prefer a [placeholder] that's already cached so that it is displayed in one
 /// frame. This prevents it from popping onto the screen.
 ///
 /// When [image] changes it is resolved to a new [ImageStream]. If the new
 /// [ImageStream.key] is different this widget subscribes to the new stream and
 /// replaces the displayed image with images emitted by the new stream.
 ///
 /// When [placeholder] changes and the [image] has not yet emitted an
 /// [ImageInfo], then [placeholder] is resolved to a new [ImageStream]. If the
 /// new [ImageStream.key] is different this widget subscribes to the new stream
 /// and replaces the displayed image to images emitted by the new stream.
 ///
 /// When either [placeholder] or [image] changes, this widget continues showing
 /// the previously loaded image (if any) until the new image provider provides a
 /// different image. This is known as "gapless playback" (see also
 /// [Image.gaplessPlayback]).
 ///
 /// ## Sample code
 ///
 /// ```dart
 /// new FadeInImage(
 ///   // here `bytes` is a Uint8List containing the bytes for the in-memory image
 ///   placeholder: new MemoryImage(bytes),
 ///   image: new NetworkImage('https://backend.example.com/image.png'),
 /// )
 /// ```
 class FadeInImage extends StatefulWidget {
   /// Creates a widget that displays a [placeholder] while an [image] is loading
   /// then cross-fades to display the [image].
   ///
   /// The [placeholder], [image], [fadeOutDuration], [fadeOutCurve],
   /// [fadeInDuration], [fadeInCurve], [alignment], [repeat], and
   /// [matchTextDirection] arguments must not be null.
   const FadeInImage({
     Key key,
     @required this.placeholder,
     @required this.image,
     this.fadeOutDuration = const Duration(milliseconds: 300),
     this.fadeOutCurve = Curves.easeOut,
     this.fadeInDuration = const Duration(milliseconds: 700),
     this.fadeInCurve = Curves.easeIn,
     this.width,
     this.height,
     this.fit,
     this.alignment = Alignment.center,
     this.repeat = ImageRepeat.noRepeat,
     this.matchTextDirection = false,
   }) : assert(placeholder != null),
        assert(image != null),
        assert(fadeOutDuration != null),
        assert(fadeOutCurve != null),
        assert(fadeInDuration != null),
        assert(fadeInCurve != null),
        assert(alignment != null),
        assert(repeat != null),
        assert(matchTextDirection != null),
        super(key: key);

   /// Creates a widget that uses a placeholder image stored in memory while
   /// loading the final image from the network.
   ///
   /// [placeholder] contains the bytes of the in-memory image.
   ///
   /// [image] is the URL of the final image.
   ///
   /// [placeholderScale] and [imageScale] are passed to their respective
   /// [ImageProvider]s (see also [ImageInfo.scale]).
   ///
   /// The [placeholder], [image], [placeholderScale], [imageScale],
   /// [fadeOutDuration], [fadeOutCurve], [fadeInDuration], [fadeInCurve],
   /// [alignment], [repeat], and [matchTextDirection] arguments must not be
   /// null.
   ///
   /// See also:
   ///
   ///  * [new Image.memory], which has more details about loading images from
   ///    memory.
   ///  * [new Image.network], which has more details about loading images from
   ///    the network.
   FadeInImage.memoryNetwork({
     Key key,
     @required Uint8List placeholder,
     @required String image,
     double placeholderScale = 1.0,
     double imageScale = 1.0,
     this.fadeOutDuration = const Duration(milliseconds: 300),
     this.fadeOutCurve = Curves.easeOut,
     this.fadeInDuration = const Duration(milliseconds: 700),
     this.fadeInCurve = Curves.easeIn,
     this.width,
     this.height,
     this.fit,
     this.alignment = Alignment.center,
     this.repeat = ImageRepeat.noRepeat,
     this.matchTextDirection = false,
   }) : assert(placeholder != null),
        assert(image != null),
        assert(placeholderScale != null),
        assert(imageScale != null),
        assert(fadeOutDuration != null),
        assert(fadeOutCurve != null),
        assert(fadeInDuration != null),
        assert(fadeInCurve != null),
        assert(alignment != null),
        assert(repeat != null),
        assert(matchTextDirection != null),
        placeholder = new MemoryImage(placeholder, scale: placeholderScale),
        image = new NetworkImage(image, scale: imageScale),
        super(key: key);

   /// Creates a widget that uses a placeholder image stored in an asset bundle
   /// while loading the final image from the network.
   ///
   /// [placeholder] is the key of the image in the asset bundle.
   ///
   /// [image] is the URL of the final image.
   ///
   /// [placeholderScale] and [imageScale] are passed to their respective
   /// [ImageProvider]s (see also [ImageInfo.scale]).
   ///
   /// If [placeholderScale] is omitted or is null, the pixel-density-aware asset
   /// resolution will be attempted for the [placeholder] image. Otherwise, the
   /// exact asset specified will be used.
   ///
   /// The [placeholder], [image], [imageScale], [fadeOutDuration],
   /// [fadeOutCurve], [fadeInDuration], [fadeInCurve], [alignment], [repeat],
   /// and [matchTextDirection] arguments must not be null.
   ///
   /// See also:
   ///
   ///  * [new Image.asset], which has more details about loading images from
   ///    asset bundles.
   ///  * [new Image.network], which has more details about loading images from
   ///    the network.
   FadeInImage.assetNetwork({
     Key key,
     @required String placeholder,
     @required String image,
     AssetBundle bundle,
     double placeholderScale,
     double imageScale = 1.0,
     this.fadeOutDuration = const Duration(milliseconds: 300),
     this.fadeOutCurve = Curves.easeOut,
     this.fadeInDuration = const Duration(milliseconds: 700),
     this.fadeInCurve = Curves.easeIn,
     this.width,
     this.height,
     this.fit,
     this.alignment = Alignment.center,
     this.repeat = ImageRepeat.noRepeat,
     this.matchTextDirection = false,
   }) : assert(placeholder != null),
        assert(image != null),
        placeholder = placeholderScale != null
          ? new ExactAssetImage(placeholder, bundle: bundle, scale: placeholderScale)
          : new AssetImage(placeholder, bundle: bundle),
        assert(imageScale != null),
        assert(fadeOutDuration != null),
        assert(fadeOutCurve != null),
        assert(fadeInDuration != null),
        assert(fadeInCurve != null),
        assert(alignment != null),
        assert(repeat != null),
        assert(matchTextDirection != null),
        image = new NetworkImage(image, scale: imageScale),
        super(key: key);

   /// Image displayed while the target [image] is loading.
   final ImageProvider placeholder;

   /// The target image that is displayed.
   final ImageProvider image;

   /// The duration of the fade-out animation for the [placeholder].
   final Duration fadeOutDuration;

   /// The curve of the fade-out animation for the [placeholder].
   final Curve fadeOutCurve;

   /// The duration of the fade-in animation for the [image].
   final Duration fadeInDuration;

   /// The curve of the fade-in animation for the [image].
   final Curve fadeInCurve;

   /// If non-null, require the image to have this width.
   ///
   /// If null, the image will pick a size that best preserves its intrinsic
   /// aspect ratio. This may result in a sudden change if the size of the
   /// placeholder image does not match that of the target image. The size is
   /// also affected by the scale factor.
   final double width;

   /// If non-null, require the image to have this height.
   ///
   /// If null, the image will pick a size that best preserves its intrinsic
   /// aspect ratio. This may result in a sudden change if the size of the
   /// placeholder image does not match that of the target image. The size is
   /// also affected by the scale factor.
   final double height;

   /// How to inscribe the image into the space allocated during layout.
   ///
   /// The default varies based on the other fields. See the discussion at
   /// [paintImage].
   final BoxFit fit;

   /// How to align the image within its bounds.
   ///
   /// The alignment aligns the given position in the image to the given position
   /// in the layout bounds. For example, a [Alignment] alignment of (-1.0,
   /// -1.0) aligns the image to the top-left corner of its layout bounds, while a
   /// [Alignment] alignment of (1.0, 1.0) aligns the bottom right of the
   /// image with the bottom right corner of its layout bounds. Similarly, an
   /// alignment of (0.0, 1.0) aligns the bottom middle of the image with the
   /// middle of the bottom edge of its layout bounds.
   ///
   /// If the [alignment] is [TextDirection]-dependent (i.e. if it is a
   /// [AlignmentDirectional]), then an ambient [Directionality] widget
   /// must be in scope.
   ///
   /// Defaults to [Alignment.center].
   ///
   /// See also:
   ///
   ///  * [Alignment], a class with convenient constants typically used to
   ///    specify an [AlignmentGeometry].
   ///  * [AlignmentDirectional], like [Alignment] for specifying alignments
   ///    relative to text direction.
   final AlignmentGeometry alignment;

   /// How to paint any portions of the layout bounds not covered by the image.
   final ImageRepeat repeat;

   /// Whether to paint the image in the direction of the [TextDirection].
   ///
   /// If this is true, then in [TextDirection.ltr] contexts, the image will be
   /// drawn with its origin in the top left (the "normal" painting direction for
   /// images); and in [TextDirection.rtl] contexts, the image will be drawn with
   /// a scaling factor of -1 in the horizontal direction so that the origin is
   /// in the top right.
   ///
   /// This is occasionally used with images in right-to-left environments, for
   /// images that were designed for left-to-right locales. Be careful, when
   /// using this, to not flip images with integral shadows, text, or other
   /// effects that will look incorrect when flipped.
   ///
   /// If this is true, there must be an ambient [Directionality] widget in
   /// scope.
   final bool matchTextDirection;

   @override
   State<StatefulWidget> createState() => new _FadeInImageState();
 }


 /// The phases a [FadeInImage] goes through.
 @visibleForTesting
 enum FadeInImagePhase {
   /// The initial state.
   ///
   /// We do not yet know whether the target image is ready and therefore no
   /// animation is necessary, or whether we need to use the placeholder and
   /// wait for the image to load.
   start,

   /// Waiting for the target image to load.
   waiting,

   /// Fading out previous image.
   fadeOut,

   /// Fading in new image.
   fadeIn,

   /// Fade-in complete.
   completed,
 }

 typedef void _ImageProviderResolverListener();

 class _ImageProviderResolver {
   _ImageProviderResolver({
     @required this.state,
     @required this.listener,
   });

   final _FadeInImageState state;
   final _ImageProviderResolverListener listener;

   FadeInImage get widget => state.widget;

   ImageStream _imageStream;
   ImageInfo _imageInfo;

   void resolve(ImageProvider provider) {
     final ImageStream oldImageStream = _imageStream;
     _imageStream = provider.resolve(createLocalImageConfiguration(
       state.context,
       size: widget.width != null && widget.height != null ? new Size(widget.width, widget.height) : null
     ));
     assert(_imageStream != null);

     if (_imageStream.key != oldImageStream?.key) {
       oldImageStream?.removeListener(_handleImageChanged);
       _imageStream.addListener(_handleImageChanged);
     }
   }

   void _handleImageChanged(ImageInfo imageInfo, bool synchronousCall) {
     _imageInfo = imageInfo;
     listener();
   }

   void stopListening() {
     _imageStream?.removeListener(_handleImageChanged);
   }
 }

 class _FadeInImageState extends State<FadeInImage> with TickerProviderStateMixin {
   _ImageProviderResolver _imageResolver;
   _ImageProviderResolver _placeholderResolver;

   AnimationController _controller;
   Animation<double> _animation;

   FadeInImagePhase _phase = FadeInImagePhase.start;
   FadeInImagePhase get phase => _phase;

   @override
   void initState() {
     _imageResolver = new _ImageProviderResolver(state: this, listener: _updatePhase);
     _placeholderResolver = new _ImageProviderResolver(state: this, listener: () {
       setState(() {
         // Trigger rebuild to display the placeholder image
       });
     });
     _controller = new AnimationController(
       value: 1.0,
       vsync: this,
     );
     _controller.addListener(() {
       setState(() {
         // Trigger rebuild to update opacity value.
       });
     });
     _controller.addStatusListener((AnimationStatus status) {
       _updatePhase();
     });
     super.initState();
   }

   @override
   void didChangeDependencies() {
     _resolveImage();
     super.didChangeDependencies();
   }

   @override
   void didUpdateWidget(FadeInImage oldWidget) {
     super.didUpdateWidget(oldWidget);
     if (widget.image != oldWidget.image || widget.placeholder != widget.placeholder)
       _resolveImage();
   }

   @override
   void reassemble() {
     _resolveImage(); // in case the image cache was flushed
     super.reassemble();
   }

   void _resolveImage() {
     _imageResolver.resolve(widget.image);

     // No need to resolve the placeholder if we are past the placeholder stage.
     if (_isShowingPlaceholder)
       _placeholderResolver.resolve(widget.placeholder);

     if (_phase == FadeInImagePhase.start)
       _updatePhase();
   }

   void _updatePhase() {
     setState(() {
       switch (_phase) {
         case FadeInImagePhase.start:
           if (_imageResolver._imageInfo != null)
             _phase = FadeInImagePhase.completed;
           else
             _phase = FadeInImagePhase.waiting;
           break;
         case FadeInImagePhase.waiting:
           if (_imageResolver._imageInfo != null) {
             // Received image data. Begin placeholder fade-out.
             _controller.duration = widget.fadeOutDuration;
             _animation = new CurvedAnimation(
               parent: _controller,
               curve: widget.fadeOutCurve,
             );
             _phase = FadeInImagePhase.fadeOut;
             _controller.reverse(from: 1.0);
           }
           break;
         case FadeInImagePhase.fadeOut:
           if (_controller.status == AnimationStatus.dismissed) {
             // Done fading out placeholder. Begin target image fade-in.
             _controller.duration = widget.fadeInDuration;
             _animation = new CurvedAnimation(
               parent: _controller,
               curve: widget.fadeInCurve,
             );
             _phase = FadeInImagePhase.fadeIn;
             _placeholderResolver.stopListening();
             _controller.forward(from: 0.0);
           }
           break;
         case FadeInImagePhase.fadeIn:
           if (_controller.status == AnimationStatus.completed) {
             // Done finding in new image.
             _phase = FadeInImagePhase.completed;
           }
           break;
         case FadeInImagePhase.completed:
           // Nothing to do.
           break;
       }
     });
   }

   @override
   void dispose() {
     _imageResolver.stopListening();
     _placeholderResolver.stopListening();
     _controller.dispose();
     super.dispose();
   }

   bool get _isShowingPlaceholder {
     assert(_phase != null);
     switch (_phase) {
       case FadeInImagePhase.start:
       case FadeInImagePhase.waiting:
       case FadeInImagePhase.fadeOut:
         return true;
       case FadeInImagePhase.fadeIn:
       case FadeInImagePhase.completed:
         return false;
     }

     return null;
   }

   ImageInfo get _imageInfo {
     return _isShowingPlaceholder
       ? _placeholderResolver._imageInfo
       : _imageResolver._imageInfo;
   }

   @override
   Widget build(BuildContext context) {
     assert(_phase != FadeInImagePhase.start);
     final ImageInfo imageInfo = _imageInfo;
     return new RawImage(
       image: imageInfo?.image,
       width: widget.width,
       height: widget.height,
       scale: imageInfo?.scale ?? 1.0,
       color: new Color.fromRGBO(255, 255, 255, _animation?.value ?? 1.0),
       colorBlendMode: BlendMode.modulate,
       fit: widget.fit,
       alignment: widget.alignment,
       repeat: widget.repeat,
       matchTextDirection: widget.matchTextDirection,
     );
   }

   @override
   void debugFillProperties(DiagnosticPropertiesBuilder description) {
     super.debugFillProperties(description);
     description.add(new EnumProperty<FadeInImagePhase>('phase', _phase));
     description.add(new DiagnosticsProperty<ImageInfo>('pixels', _imageInfo));
     description.add(new DiagnosticsProperty<ImageStream>('image stream', _imageResolver._imageStream));
     description.add(new DiagnosticsProperty<ImageStream>('placeholder stream', _placeholderResolver._imageStream));
   }
 }
	// Copyright 2017 The Chromium Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	import 'dart:typed_data';

	import 'package:flutter/foundation.dart';
	import 'package:flutter/services.dart';

	import 'basic.dart';
	import 'framework.dart';
	import 'image.dart';
	import 'ticker_provider.dart';

	// Examples can assume:
	// Uint8List bytes;

	/// An image that shows a [placeholder] image while the target [image] is
	/// loading, then fades in the new image when it loads.
	///
	/// Use this class to display long-loading images, such as [new NetworkImage],
	/// so that the image appears on screen with a graceful animation rather than
	/// abruptly pops onto the screen.
	///
	/// If the [image] emits an [ImageInfo] synchronously, such as when the image
	/// has been loaded and cached, the [image] is displayed immediately and the
	/// [placeholder] is never displayed.
	///
	/// [fadeOutDuration] and [fadeOutCurve] control the fade-out animation of the
	/// placeholder.
	///
	/// [fadeInDuration] and [fadeInCurve] control the fade-in animation of the
	/// target [image].
	///
	/// Prefer a [placeholder] that's already cached so that it is displayed in one
	/// frame. This prevents it from popping onto the screen.
	///
	/// When [image] changes it is resolved to a new [ImageStream]. If the new
	/// [ImageStream.key] is different this widget subscribes to the new stream and
	/// replaces the displayed image with images emitted by the new stream.
	///
	/// When [placeholder] changes and the [image] has not yet emitted an
	/// [ImageInfo], then [placeholder] is resolved to a new [ImageStream]. If the
	/// new [ImageStream.key] is different this widget subscribes to the new stream
	/// and replaces the displayed image to images emitted by the new stream.
	///
	/// When either [placeholder] or [image] changes, this widget continues showing
	/// the previously loaded image (if any) until the new image provider provides a
	/// different image. This is known as "gapless playback" (see also
	/// [Image.gaplessPlayback]).
	///
	/// ## Sample code
	///
	/// ```dart
	/// new FadeInImage(
	/// // here `bytes` is a Uint8List containing the bytes for the in-memory image
	/// placeholder: new MemoryImage(bytes),
	/// image: new NetworkImage('https://backend.example.com/image.png'),
	/// )
	/// ```
	class FadeInImage extends StatefulWidget {
	/// Creates a widget that displays a [placeholder] while an [image] is loading
	/// then cross-fades to display the [image].
	///
	/// The [placeholder], [image], [fadeOutDuration], [fadeOutCurve],
	/// [fadeInDuration], [fadeInCurve], [alignment], [repeat], and
	/// [matchTextDirection] arguments must not be null.
	const FadeInImage({
	Key key,
	@required this.placeholder,
	@required this.image,
	this.fadeOutDuration = const Duration(milliseconds: 300),
	this.fadeOutCurve = Curves.easeOut,
	this.fadeInDuration = const Duration(milliseconds: 700),
	this.fadeInCurve = Curves.easeIn,
	this.width,
	this.height,
	this.fit,
	this.alignment = Alignment.center,
	this.repeat = ImageRepeat.noRepeat,
	this.matchTextDirection = false,
	}) : assert(placeholder != null),
	assert(image != null),
	assert(fadeOutDuration != null),
	assert(fadeOutCurve != null),
	assert(fadeInDuration != null),
	assert(fadeInCurve != null),
	assert(alignment != null),
	assert(repeat != null),
	assert(matchTextDirection != null),
	super(key: key);

	/// Creates a widget that uses a placeholder image stored in memory while
	/// loading the final image from the network.
	///
	/// [placeholder] contains the bytes of the in-memory image.
	///
	/// [image] is the URL of the final image.
	///
	/// [placeholderScale] and [imageScale] are passed to their respective
	/// [ImageProvider]s (see also [ImageInfo.scale]).
	///
	/// The [placeholder], [image], [placeholderScale], [imageScale],
	/// [fadeOutDuration], [fadeOutCurve], [fadeInDuration], [fadeInCurve],
	/// [alignment], [repeat], and [matchTextDirection] arguments must not be
	/// null.
	///
	/// See also:
	///
	/// * [new Image.memory], which has more details about loading images from
	/// memory.
	/// * [new Image.network], which has more details about loading images from
	/// the network.
	FadeInImage.memoryNetwork({
	Key key,
	@required Uint8List placeholder,
	@required String image,
	double placeholderScale = 1.0,
	double imageScale = 1.0,
	this.fadeOutDuration = const Duration(milliseconds: 300),
	this.fadeOutCurve = Curves.easeOut,
	this.fadeInDuration = const Duration(milliseconds: 700),
	this.fadeInCurve = Curves.easeIn,
	this.width,
	this.height,
	this.fit,
	this.alignment = Alignment.center,
	this.repeat = ImageRepeat.noRepeat,
	this.matchTextDirection = false,
	}) : assert(placeholder != null),
	assert(image != null),
	assert(placeholderScale != null),
	assert(imageScale != null),
	assert(fadeOutDuration != null),
	assert(fadeOutCurve != null),
	assert(fadeInDuration != null),
	assert(fadeInCurve != null),
	assert(alignment != null),
	assert(repeat != null),
	assert(matchTextDirection != null),
	placeholder = new MemoryImage(placeholder, scale: placeholderScale),
	image = new NetworkImage(image, scale: imageScale),
	super(key: key);

	/// Creates a widget that uses a placeholder image stored in an asset bundle
	/// while loading the final image from the network.
	///
	/// [placeholder] is the key of the image in the asset bundle.
	///
	/// [image] is the URL of the final image.
	///
	/// [placeholderScale] and [imageScale] are passed to their respective
	/// [ImageProvider]s (see also [ImageInfo.scale]).
	///
	/// If [placeholderScale] is omitted or is null, the pixel-density-aware asset
	/// resolution will be attempted for the [placeholder] image. Otherwise, the
	/// exact asset specified will be used.
	///
	/// The [placeholder], [image], [imageScale], [fadeOutDuration],
	/// [fadeOutCurve], [fadeInDuration], [fadeInCurve], [alignment], [repeat],
	/// and [matchTextDirection] arguments must not be null.
	///
	/// See also:
	///
	/// * [new Image.asset], which has more details about loading images from
	/// asset bundles.
	/// * [new Image.network], which has more details about loading images from
	/// the network.
	FadeInImage.assetNetwork({
	Key key,
	@required String placeholder,
	@required String image,
	AssetBundle bundle,
	double placeholderScale,
	double imageScale = 1.0,
	this.fadeOutDuration = const Duration(milliseconds: 300),
	this.fadeOutCurve = Curves.easeOut,
	this.fadeInDuration = const Duration(milliseconds: 700),
	this.fadeInCurve = Curves.easeIn,
	this.width,
	this.height,
	this.fit,
	this.alignment = Alignment.center,
	this.repeat = ImageRepeat.noRepeat,
	this.matchTextDirection = false,
	}) : assert(placeholder != null),
	assert(image != null),
	placeholder = placeholderScale != null
	? new ExactAssetImage(placeholder, bundle: bundle, scale: placeholderScale)
	: new AssetImage(placeholder, bundle: bundle),
	assert(imageScale != null),
	assert(fadeOutDuration != null),
	assert(fadeOutCurve != null),
	assert(fadeInDuration != null),
	assert(fadeInCurve != null),
	assert(alignment != null),
	assert(repeat != null),
	assert(matchTextDirection != null),
	image = new NetworkImage(image, scale: imageScale),
	super(key: key);

	/// Image displayed while the target [image] is loading.
	final ImageProvider placeholder;

	/// The target image that is displayed.
	final ImageProvider image;

	/// The duration of the fade-out animation for the [placeholder].
	final Duration fadeOutDuration;

	/// The curve of the fade-out animation for the [placeholder].
	final Curve fadeOutCurve;

	/// The duration of the fade-in animation for the [image].
	final Duration fadeInDuration;

	/// The curve of the fade-in animation for the [image].
	final Curve fadeInCurve;

	/// If non-null, require the image to have this width.
	///
	/// If null, the image will pick a size that best preserves its intrinsic
	/// aspect ratio. This may result in a sudden change if the size of the
	/// placeholder image does not match that of the target image. The size is
	/// also affected by the scale factor.
	final double width;

	/// If non-null, require the image to have this height.
	///
	/// If null, the image will pick a size that best preserves its intrinsic
	/// aspect ratio. This may result in a sudden change if the size of the
	/// placeholder image does not match that of the target image. The size is
	/// also affected by the scale factor.
	final double height;

	/// How to inscribe the image into the space allocated during layout.
	///
	/// The default varies based on the other fields. See the discussion at
	/// [paintImage].
	final BoxFit fit;

	/// How to align the image within its bounds.
	///
	/// The alignment aligns the given position in the image to the given position
	/// in the layout bounds. For example, a [Alignment] alignment of (-1.0,
	/// -1.0) aligns the image to the top-left corner of its layout bounds, while a
	/// [Alignment] alignment of (1.0, 1.0) aligns the bottom right of the
	/// image with the bottom right corner of its layout bounds. Similarly, an
	/// alignment of (0.0, 1.0) aligns the bottom middle of the image with the
	/// middle of the bottom edge of its layout bounds.
	///
	/// If the [alignment] is [TextDirection]-dependent (i.e. if it is a
	/// [AlignmentDirectional]), then an ambient [Directionality] widget
	/// must be in scope.
	///
	/// Defaults to [Alignment.center].
	///
	/// See also:
	///
	/// * [Alignment], a class with convenient constants typically used to
	/// specify an [AlignmentGeometry].
	/// * [AlignmentDirectional], like [Alignment] for specifying alignments
	/// relative to text direction.
	final AlignmentGeometry alignment;

	/// How to paint any portions of the layout bounds not covered by the image.
	final ImageRepeat repeat;

	/// Whether to paint the image in the direction of the [TextDirection].
	///
	/// If this is true, then in [TextDirection.ltr] contexts, the image will be
	/// drawn with its origin in the top left (the "normal" painting direction for
	/// images); and in [TextDirection.rtl] contexts, the image will be drawn with
	/// a scaling factor of -1 in the horizontal direction so that the origin is
	/// in the top right.
	///
	/// This is occasionally used with images in right-to-left environments, for
	/// images that were designed for left-to-right locales. Be careful, when
	/// using this, to not flip images with integral shadows, text, or other
	/// effects that will look incorrect when flipped.
	///
	/// If this is true, there must be an ambient [Directionality] widget in
	/// scope.
	final bool matchTextDirection;

	@override
	State<StatefulWidget> createState() => new _FadeInImageState();
	}


	/// The phases a [FadeInImage] goes through.
	@visibleForTesting
	enum FadeInImagePhase {
	/// The initial state.
	///
	/// We do not yet know whether the target image is ready and therefore no
	/// animation is necessary, or whether we need to use the placeholder and
	/// wait for the image to load.
	start,

	/// Waiting for the target image to load.
	waiting,

	/// Fading out previous image.
	fadeOut,

	/// Fading in new image.
	fadeIn,

	/// Fade-in complete.
	completed,
	}

	typedef void _ImageProviderResolverListener();

	class _ImageProviderResolver {
	_ImageProviderResolver({
	@required this.state,
	@required this.listener,
	});

	final _FadeInImageState state;
	final _ImageProviderResolverListener listener;

	FadeInImage get widget => state.widget;

	ImageStream _imageStream;
	ImageInfo _imageInfo;

	void resolve(ImageProvider provider) {
	final ImageStream oldImageStream = _imageStream;
	_imageStream = provider.resolve(createLocalImageConfiguration(
	state.context,
	size: widget.width != null && widget.height != null ? new Size(widget.width, widget.height) : null
	));
	assert(_imageStream != null);

	if (_imageStream.key != oldImageStream?.key) {
	oldImageStream?.removeListener(_handleImageChanged);
	_imageStream.addListener(_handleImageChanged);
	}
	}

	void _handleImageChanged(ImageInfo imageInfo, bool synchronousCall) {
	_imageInfo = imageInfo;
	listener();
	}

	void stopListening() {
	_imageStream?.removeListener(_handleImageChanged);
	}
	}

	class _FadeInImageState extends State<FadeInImage> with TickerProviderStateMixin {
	_ImageProviderResolver _imageResolver;
	_ImageProviderResolver _placeholderResolver;

	AnimationController _controller;
	Animation<double> _animation;

	FadeInImagePhase _phase = FadeInImagePhase.start;
	FadeInImagePhase get phase => _phase;

	@override
	void initState() {
	_imageResolver = new _ImageProviderResolver(state: this, listener: _updatePhase);
	_placeholderResolver = new _ImageProviderResolver(state: this, listener: () {
	setState(() {
	// Trigger rebuild to display the placeholder image
	});
	});
	_controller = new AnimationController(
	value: 1.0,
	vsync: this,
	);
	_controller.addListener(() {
	setState(() {
	// Trigger rebuild to update opacity value.
	});
	});
	_controller.addStatusListener((AnimationStatus status) {
	_updatePhase();
	});
	super.initState();
	}

	@override
	void didChangeDependencies() {
	_resolveImage();
	super.didChangeDependencies();
	}

	@override
	void didUpdateWidget(FadeInImage oldWidget) {
	super.didUpdateWidget(oldWidget);
	if (widget.image != oldWidget.image \|\| widget.placeholder != widget.placeholder)
	_resolveImage();
	}

	@override
	void reassemble() {
	_resolveImage(); // in case the image cache was flushed
	super.reassemble();
	}

	void _resolveImage() {
	_imageResolver.resolve(widget.image);

	// No need to resolve the placeholder if we are past the placeholder stage.
	if (_isShowingPlaceholder)
	_placeholderResolver.resolve(widget.placeholder);

	if (_phase == FadeInImagePhase.start)
	_updatePhase();
	}

	void _updatePhase() {
	setState(() {
	switch (_phase) {
	case FadeInImagePhase.start:
	if (_imageResolver._imageInfo != null)
	_phase = FadeInImagePhase.completed;
	else
	_phase = FadeInImagePhase.waiting;
	break;
	case FadeInImagePhase.waiting:
	if (_imageResolver._imageInfo != null) {
	// Received image data. Begin placeholder fade-out.
	_controller.duration = widget.fadeOutDuration;
	_animation = new CurvedAnimation(
	parent: _controller,
	curve: widget.fadeOutCurve,
	);
	_phase = FadeInImagePhase.fadeOut;
	_controller.reverse(from: 1.0);
	}
	break;
	case FadeInImagePhase.fadeOut:
	if (_controller.status == AnimationStatus.dismissed) {
	// Done fading out placeholder. Begin target image fade-in.
	_controller.duration = widget.fadeInDuration;
	_animation = new CurvedAnimation(
	parent: _controller,
	curve: widget.fadeInCurve,
	);
	_phase = FadeInImagePhase.fadeIn;
	_placeholderResolver.stopListening();
	_controller.forward(from: 0.0);
	}
	break;
	case FadeInImagePhase.fadeIn:
	if (_controller.status == AnimationStatus.completed) {
	// Done finding in new image.
	_phase = FadeInImagePhase.completed;
	}
	break;
	case FadeInImagePhase.completed:
	// Nothing to do.
	break;
	}
	});
	}

	@override
	void dispose() {
	_imageResolver.stopListening();
	_placeholderResolver.stopListening();
	_controller.dispose();
	super.dispose();
	}

	bool get _isShowingPlaceholder {
	assert(_phase != null);
	switch (_phase) {
	case FadeInImagePhase.start:
	case FadeInImagePhase.waiting:
	case FadeInImagePhase.fadeOut:
	return true;
	case FadeInImagePhase.fadeIn:
	case FadeInImagePhase.completed:
	return false;
	}

	return null;
	}

	ImageInfo get _imageInfo {
	return _isShowingPlaceholder
	? _placeholderResolver._imageInfo
	: _imageResolver._imageInfo;
	}

	@override
	Widget build(BuildContext context) {
	assert(_phase != FadeInImagePhase.start);
	final ImageInfo imageInfo = _imageInfo;
	return new RawImage(
	image: imageInfo?.image,
	width: widget.width,
	height: widget.height,
	scale: imageInfo?.scale ?? 1.0,
	color: new Color.fromRGBO(255, 255, 255, _animation?.value ?? 1.0),
	colorBlendMode: BlendMode.modulate,
	fit: widget.fit,
	alignment: widget.alignment,
	repeat: widget.repeat,
	matchTextDirection: widget.matchTextDirection,
	);
	}

	@override
	void debugFillProperties(DiagnosticPropertiesBuilder description) {
	super.debugFillProperties(description);
	description.add(new EnumProperty<FadeInImagePhase>('phase', _phase));
	description.add(new DiagnosticsProperty<ImageInfo>('pixels', _imageInfo));
	description.add(new DiagnosticsProperty<ImageStream>('image stream', _imageResolver._imageStream));
	description.add(new DiagnosticsProperty<ImageStream>('placeholder stream', _placeholderResolver._imageStream));
	}
	}