FadeInImage cacheWidth and cacheHeight support (#43286)

packages/flutter/lib/src/painting/image_provider.dart

@@ -540,6 +540,18 @@ class ResizeImage extends ImageProvider<_SizeAwareCacheKey> {
   /// The height the image should decode to and cache.
   final int height;
 
+  /// Composes the `provider` in a [ResizeImage] only when `cacheWidth` and
+  /// `cacheHeight` are not both null.
+  ///
+  /// When `cacheWidth` and `cacheHeight` are both null, this will return the
+  /// `provider` directly.
+  static ImageProvider<dynamic> resizeIfNeeded(int cacheWidth, int cacheHeight, ImageProvider<dynamic> provider) {
+    if (cacheWidth != null || cacheHeight != null) {
+      return ResizeImage(provider, width: cacheWidth, height: cacheHeight);
+    }
+    return provider;
+  }
+
   @override
   ImageStreamCompleter load(_SizeAwareCacheKey key, DecoderCallback decode) {
     final DecoderCallback decodeResize = (Uint8List bytes, {int cacheWidth, int cacheHeight}) {

packages/flutter/lib/src/widgets/fade_in_image.dart

@@ -66,6 +66,9 @@ class FadeInImage extends StatelessWidget {
   /// Creates a widget that displays a [placeholder] while an [image] is loading,
   /// then fades-out the placeholder and fades-in the image.
   ///
+  /// The [placeholder] and [image] may be composed in a [ResizeImage] to provide
+  /// a custom decode/cache size.
+  ///
   /// The [placeholder], [image], [fadeOutDuration], [fadeOutCurve],
   /// [fadeInDuration], [fadeInCurve], [alignment], [repeat], and
   /// [matchTextDirection] arguments must not be null.
@@ -108,6 +111,13 @@ class FadeInImage extends StatelessWidget {
   /// The `placeholderScale` and `imageScale` arguments are passed to their
   /// respective [ImageProvider]s (see also [ImageInfo.scale]).
   ///
+  /// If [placeholderCacheWidth], [placeholderCacheHeight], [imageCacheWidth],
+  /// or [imageCacheHeight] are provided, it indicates to the
+  /// engine that the respective image should be decoded at the specified size.
+  /// The image will be rendered to the constraints of the layout or [width]
+  /// and [height] regardless of these parameters. These parameters are primarily
+  /// intended to reduce the memory usage of [ImageCache].
+  ///
   /// The [placeholder], [image], [placeholderScale], [imageScale],
   /// [fadeOutDuration], [fadeOutCurve], [fadeInDuration], [fadeInCurve],
   /// [alignment], [repeat], and [matchTextDirection] arguments must not be
@@ -137,6 +147,10 @@ class FadeInImage extends StatelessWidget {
     this.alignment = Alignment.center,
     this.repeat = ImageRepeat.noRepeat,
     this.matchTextDirection = false,
+    int placeholderCacheWidth,
+    int placeholderCacheHeight,
+    int imageCacheWidth,
+    int imageCacheHeight,
   }) : assert(placeholder != null),
        assert(image != null),
        assert(placeholderScale != null),
@@ -148,8 +162,8 @@ class FadeInImage extends StatelessWidget {
        assert(alignment != null),
        assert(repeat != null),
        assert(matchTextDirection != null),
-       placeholder = MemoryImage(placeholder, scale: placeholderScale),
-       image = NetworkImage(image, scale: imageScale),
+       placeholder = ResizeImage.resizeIfNeeded(placeholderCacheWidth, placeholderCacheHeight, MemoryImage(placeholder, scale: placeholderScale)),
+       image = ResizeImage.resizeIfNeeded(imageCacheWidth, imageCacheHeight, NetworkImage(image, scale: imageScale)),
        super(key: key);
 
   /// Creates a widget that uses a placeholder image stored in an asset bundle
@@ -166,6 +180,13 @@ class FadeInImage extends StatelessWidget {
   /// resolution will be attempted for the [placeholder] image. Otherwise, the
   /// exact asset specified will be used.
   ///
+  /// If [placeholderCacheWidth], [placeholderCacheHeight], [imageCacheWidth],
+  /// or [imageCacheHeight] are provided, it indicates to the
+  /// engine that the respective image should be decoded at the specified size.
+  /// The image will be rendered to the constraints of the layout or [width]
+  /// and [height] regardless of these parameters. These parameters are primarily
+  /// intended to reduce the memory usage of [ImageCache].
+  ///
   /// The [placeholder], [image], [imageScale], [fadeOutDuration],
   /// [fadeOutCurve], [fadeInDuration], [fadeInCurve], [alignment], [repeat],
   /// and [matchTextDirection] arguments must not be null.
@@ -195,11 +216,15 @@ class FadeInImage extends StatelessWidget {
     this.alignment = Alignment.center,
     this.repeat = ImageRepeat.noRepeat,
     this.matchTextDirection = false,
+    int placeholderCacheWidth,
+    int placeholderCacheHeight,
+    int imageCacheWidth,
+    int imageCacheHeight,
   }) : assert(placeholder != null),
        assert(image != null),
        placeholder = placeholderScale != null
-         ? ExactAssetImage(placeholder, bundle: bundle, scale: placeholderScale)
-         : AssetImage(placeholder, bundle: bundle),
+         ? ResizeImage.resizeIfNeeded(placeholderCacheWidth, placeholderCacheHeight, ExactAssetImage(placeholder, bundle: bundle, scale: placeholderScale))
+         : ResizeImage.resizeIfNeeded(placeholderCacheWidth, placeholderCacheHeight, AssetImage(placeholder, bundle: bundle)),
        assert(imageScale != null),
        assert(fadeOutDuration != null),
        assert(fadeOutCurve != null),
@@ -208,7 +233,7 @@ class FadeInImage extends StatelessWidget {
        assert(alignment != null),
        assert(repeat != null),
        assert(matchTextDirection != null),
-       image = NetworkImage(image, scale: imageScale),
+       image = ResizeImage.resizeIfNeeded(imageCacheWidth, imageCacheHeight, NetworkImage(image, scale: imageScale)),
        super(key: key);
 
   /// Image displayed while the target [image] is loading.

packages/flutter/lib/src/widgets/image.dart

@@ -55,13 +55,6 @@ ImageConfiguration createLocalImageConfiguration(BuildContext context, { Size si
   );
 }
 
-ImageProvider<dynamic> _resizeIfNeeded(int cacheWidth, int cacheHeight, ImageProvider<dynamic> provider) {
-  if (cacheWidth != null || cacheHeight != null) {
-    return ResizeImage(provider, width: cacheWidth, height: cacheHeight);
-  }
-  return provider;
-}
-
 /// Prefetches an image into the image cache.
 ///
 /// Returns a [Future] that will complete when the first image yielded by the
@@ -358,7 +351,7 @@ class Image extends StatefulWidget {
     Map<String, String> headers,
     int cacheWidth,
     int cacheHeight,
-  }) : image = _resizeIfNeeded(cacheWidth, cacheHeight, NetworkImage(src, scale: scale, headers: headers)),
+  }) : image = ResizeImage.resizeIfNeeded(cacheWidth, cacheHeight, NetworkImage(src, scale: scale, headers: headers)),
        assert(alignment != null),
        assert(repeat != null),
        assert(matchTextDirection != null),
@@ -410,7 +403,7 @@ class Image extends StatefulWidget {
     this.filterQuality = FilterQuality.low,
     int cacheWidth,
     int cacheHeight,
-  }) : image = _resizeIfNeeded(cacheWidth, cacheHeight, FileImage(file, scale: scale)),
+  }) : image = ResizeImage.resizeIfNeeded(cacheWidth, cacheHeight, FileImage(file, scale: scale)),
        loadingBuilder = null,
        assert(alignment != null),
        assert(repeat != null),
@@ -573,7 +566,7 @@ class Image extends StatefulWidget {
     this.filterQuality = FilterQuality.low,
     int cacheWidth,
     int cacheHeight,
-  }) : image = _resizeIfNeeded(cacheWidth, cacheHeight, scale != null
+  }) : image = ResizeImage.resizeIfNeeded(cacheWidth, cacheHeight, scale != null
          ? ExactAssetImage(name, bundle: bundle, scale: scale, package: package)
          : AssetImage(name, bundle: bundle, package: package)
        ),
@@ -630,7 +623,7 @@ class Image extends StatefulWidget {
     this.filterQuality = FilterQuality.low,
     int cacheWidth,
     int cacheHeight,
-  }) : image = _resizeIfNeeded(cacheWidth, cacheHeight, MemoryImage(bytes, scale: scale)),
+  }) : image = ResizeImage.resizeIfNeeded(cacheWidth, cacheHeight, MemoryImage(bytes, scale: scale)),
        loadingBuilder = null,
        assert(alignment != null),
        assert(repeat != null),

packages/flutter/test/widgets/fade_in_image_test.dart

@@ -3,10 +3,13 @@
 // found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:typed_data';
 import 'dart:ui' as ui;
 
 import 'package:flutter/widgets.dart';
+import 'package:flutter/painting.dart';
 import 'package:flutter_test/flutter_test.dart';
+import '../painting/image_data.dart';
 import '../painting/image_test_utils.dart';
 
 const Duration animationDuration = Duration(milliseconds: 50);
@@ -51,6 +54,26 @@ class FadeInImageElements {
   double get opacity => fadeTransition == null ? 1 : fadeTransition.opacity.value;
 }
 
+class LoadTestImageProvider extends ImageProvider<dynamic> {
+  LoadTestImageProvider(this.provider);
+
+  final ImageProvider provider;
+
+  ImageStreamCompleter testLoad(dynamic key, DecoderCallback decode) {
+    return provider.load(key, decode);
+  }
+
+  @override
+  Future<dynamic> obtainKey(ImageConfiguration configuration) {
+    return null;
+  }
+
+  @override
+  ImageStreamCompleter load(dynamic key, DecoderCallback decode) {
+    return null;
+  }
+}
+
 FadeInImageParts findFadeInImage(WidgetTester tester) {
   final List<FadeInImageElements> elements = <FadeInImageElements>[];
   final Iterable<Element> rawImageElements = tester.elementList(find.byType(RawImage));
@@ -262,6 +285,58 @@ Future<void> main() async {
       expect(findFadeInImage(tester).target.opacity, moreOrLessEquals(1));
     });
 
+    group(ImageProvider, () {
+
+      testWidgets('memory placeholder cacheWidth and cacheHeight is passed through', (WidgetTester tester) async {
+        final Uint8List testBytes = Uint8List.fromList(kTransparentImage);
+        final FadeInImage image = FadeInImage.memoryNetwork(
+          placeholder: testBytes,
+          image: 'test.com',
+          placeholderCacheWidth: 20,
+          placeholderCacheHeight: 30,
+          imageCacheWidth: 40,
+          imageCacheHeight: 50,
+        );
+
+        bool called = false;
+        final DecoderCallback decode = (Uint8List bytes, {int cacheWidth, int cacheHeight}) {
+          expect(cacheWidth, 20);
+          expect(cacheHeight, 30);
+          called = true;
+          return PaintingBinding.instance.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight);
+        };
+        final ImageProvider resizeImage = image.placeholder;
+        expect(image.placeholder, isA<ResizeImage>());
+        expect(called, false);
+        final LoadTestImageProvider testProvider = LoadTestImageProvider(image.placeholder);
+        testProvider.testLoad(await resizeImage.obtainKey(ImageConfiguration.empty), decode);
+        expect(called, true);
+      });
+
+      testWidgets('do not resize when null cache dimensions', (WidgetTester tester) async {
+        final Uint8List testBytes = Uint8List.fromList(kTransparentImage);
+        final FadeInImage image = FadeInImage.memoryNetwork(
+          placeholder: testBytes,
+          image: 'test.com',
+        );
+
+        bool called = false;
+        final DecoderCallback decode = (Uint8List bytes, {int cacheWidth, int cacheHeight}) {
+          expect(cacheWidth, null);
+          expect(cacheHeight, null);
+          called = true;
+          return PaintingBinding.instance.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight);
+        };
+        // image.placeholder should be an instance of MemoryImage instead of ResizeImage
+        final ImageProvider memoryImage = image.placeholder;
+        expect(image.placeholder, isA<MemoryImage>());
+        expect(called, false);
+        final LoadTestImageProvider testProvider = LoadTestImageProvider(image.placeholder);
+        testProvider.testLoad(await memoryImage.obtainKey(ImageConfiguration.empty), decode);
+        expect(called, true);
+      });
+    });
+
     group('semantics', () {
       testWidgets('only one Semantics node appears within FadeInImage', (WidgetTester tester) async {
         final TestImageProvider placeholderProvider = TestImageProvider(placeholderImage);