Overview
========
This patch refactors images to achieve the following goals:
* it allows references to unresolved assets to be passed
around (previously, almost every layer of the system had to know about
whether an image came from an asset bundle or the network or
elsewhere, and had to manually interact with the image cache).
* it allows decorations to use the same API for declaring images as the
widget tree.
It requires some minor changes to call sites that use images, as
discussed below.
Widgets
-------
Change this:
```dart
child: new AssetImage(
name: 'my_asset.png',
...
)
```
...to this:
```dart
child: new Image(
image: new AssetImage('my_asset.png'),
...
)
```
Decorations
-----------
Change this:
```dart
child: new DecoratedBox(
decoration: new BoxDecoration(
backgroundImage: new BackgroundImage(
image: DefaultAssetBundle.of(context).loadImage('my_asset.png'),
...
),
...
),
child: ...
)
```
...to this:
```dart
child: new DecoratedBox(
decoration: new BoxDecoration(
backgroundImage: new BackgroundImage(
image: new AssetImage('my_asset.png'),
...
),
...
),
child: ...
)
```
DETAILED CHANGE LOG
===================
The following APIs have been replaced in this patch:
* The `AssetImage` and `NetworkImage` widgets have been split in two,
with identically-named `ImageProvider` subclasses providing the
image-loading logic, and a single `Image` widget providing all the
widget tree logic.
* `ImageResource` is now `ImageStream`. Rather than configuring it with
a `Future<ImageInfo>`, you complete it with an `ImageStreamCompleter`.
* `ImageCache.load` and `ImageCache.loadProvider` are replaced by
`ImageCache.putIfAbsent`.
The following APIs have changed in this patch:
* `ImageCache` works in terms of arbitrary keys and caches
`ImageStreamCompleter` objects using those keys. With the new model,
you should never need to interact with the cache directly.
* `Decoration` can now be `const`. The state has moved to the
`BoxPainter` class. Instead of a list of listeners, there's now just a
single callback and a `dispose()` method on the painter. The callback
is passed in to the `createBoxPainter()` method. When invoked, you
should repaint the painter.
The following new APIs are introduced:
* `AssetBundle.loadStructuredData`.
* `SynchronousFuture`, a variant of `Future` that calls the `then`
callback synchronously. This enables the asynchronous and
synchronous (in-the-cache) code paths to look identical yet for the
latter to avoid returning to the event loop mid-paint.
* `ExactAssetImage`, a variant of `AssetImage` that doesn't do anything clever.
* `ImageConfiguration`, a class that describes parameters that configure
the `AssetImage` resolver.
The following APIs are entirely removed by this patch:
* `AssetBundle.loadImage` is gone. Use an `AssetImage` instead.
* `AssetVendor` is gone. `AssetImage` handles everything `AssetVendor`
used to handle.
* `RawImageResource` and `AsyncImage` are gone.
The following code-level changes are performed:
* `Image`, which replaces `AsyncImage`, `NetworkImage`, `AssetImage`,
and `RawResourceImage`, lives in `image.dart`.
* `DecoratedBox` and `Container` live in their own file now,
`container.dart` (they reference `image.dart`).
DIRECTIONS FOR FUTURE RESEARCH
==============================
* The `ImageConfiguration` fields are mostly aspirational. Right now
only `devicePixelRatio` and `bundle` are implemented. `locale` isn't
even plumbed through, it will require work on the localisation logic.
* We should go through and make `BoxDecoration`, `AssetImage`, and
`NetworkImage` objects `const` where possible.
* This patch makes supporting animated GIFs much easier.
* This patch makes it possible to create an abstract concept of an
"Icon" that could be either an image or a font-based glyph (using
`IconData` or similar). (see
https://github.com/flutter/flutter/issues/4494)
RELATED ISSUES
==============
Fixes https://github.com/flutter/flutter/issues/4500
Fixes https://github.com/flutter/flutter/issues/4495
Obsoletes https://github.com/flutter/flutter/issues/4496
This makes it possible to substitute 'flutter run' for 'flutter test'
and actually watch a test run on a device.
For any test that depends on flutter_test:
1. Remove any import of 'package:test/test.dart'.
2. Replace `testWidgets('...', (WidgetTester tester) {`
with `testWidgets('...', (WidgetTester tester) async {`
3. Add an "await" in front of calls to any of the following:
* tap()
* tapAt()
* fling()
* flingFrom()
* scroll()
* scrollAt()
* pump()
* pumpWidget()
4. Replace any calls to `tester.flushMicrotasks()` with calls to
`await tester.idle()`.
There's a guarding API that you can use, if you have particularly
complicated tests, to get better error messages. Search for
TestAsyncUtils.
* Refactor widget test framework
Instead of:
```dart
test("Card Collection smoke test", () {
testWidgets((WidgetTester tester) {
```
...you now say:
```dart
testWidgets("Card Collection smoke test", (WidgetTester tester) {
```
Instead of:
```dart
expect(tester, hasWidget(find.text('hello')));
```
...you now say:
```dart
expect(find.text('hello'), findsOneWidget);
```
Instead of the previous API (exists, widgets, widget, stateOf,
elementOf, etc), you now have the following comprehensive API. All these
are functions that take a Finder, except the all* properties.
* `any()` - true if anything matches, c.f. `Iterable.any`
* `allWidgets` - all the widgets in the tree
* `widget()` - the one and only widget that matches the finder
* `firstWidget()` - the first widget that matches the finder
* `allElements` - all the elements in the tree
* `element()` - the one and only element that matches the finder
* `firstElement()` - the first element that matches the finder
* `allStates` - all the `State`s in the tree
* `state()` - the one and only state that matches the finder
* `firstState()` - the first state that matches the finder
* `allRenderObjects` - all the render objects in the tree
* `renderObject()` - the one and only render object that matches the finder
* `firstRenderObject()` - the first render object that matches the finder
There's also `layers' which returns the list of current layers.
`tap`, `fling`, getCenter, getSize, etc, take Finders, like the APIs
above, and expect there to only be one matching widget.
The finders are:
* `find.text(String text)`
* `find.widgetWithText(Type widgetType, String text)`
* `find.byKey(Key key)`
* `find.byType(Type type)`
* `find.byElementType(Type type)`
* `find.byConfig(Widget config)`
* `find.byWidgetPredicate(WidgetPredicate predicate)`
* `find.byElementPredicate(ElementPredicate predicate)`
The matchers (for `expect`) are:
* `findsNothing`
* `findsWidgets`
* `findsOneWidget`
* `findsNWidgets(n)`
* `isOnStage`
* `isOffStage`
* `isInCard`
* `isNotInCard`
Benchmarks now use benchmarkWidgets instead of testWidgets.
Also, for those of you using mockers, `serviceMocker` now automatically
handles the binding initialization.
This patch also:
* changes how tests are run so that we can more easily swap the logic
out for a "real" mode instead of FakeAsync.
* introduces CachingIterable.
* changes how flutter_driver interacts with the widget tree to use the
aforementioned new API rather than ElementTreeTester, which is gone.
* removes ElementTreeTester.
* changes the semantics of a test for scrollables because we couldn't
convince ourselves that the old semantics made sense; it only worked
before because flushing the microtasks after every event was broken.
* fixes the flushing of microtasks after every event.
* Reindent the tests
* Fix review comments
- Create a FlutterErrorDetails struct-like class that describes an
exception along with more details that aren't in the exception, like
where it was caught and what was going on when it was caught.
- Provide a FlutterError static API for handling these objects:
- FlutterError.onError which is called whenever Flutter catches an
error.
- FlutterError.reportError() which handles an error.
- FlutterError.dumpErrorToConsole() which is the default behavior
for onError.
- Removes all the existing exception handler callbacks.
- Replaces all the existing places that described exceptions using
debugPrint with calls to FlutterError.reportError().
- Extend lockState() to also catch exceptions, so that we catch
exceptions that happen during finalizers.
- Make the test framework catch errors and treat them as failures.
- Provide a mechanism to override this behavior in the test framework.
- Make the tests that used to depend on the exception handler
callbacks use this new mechanism.
- Make pump() also support the phase argument.
- Improve some tests using these new features.
Fixes#2356, #2988, #2985, #2220.
