The problem was that the Scaffold was getting a new key each time we
navigated to the main page. The key influences where page state is
stored, including the scroll offset. So for a single frame, the Scaffold
incorrectly thinks the scroll offset is 0 and the app bar should be
expanded.
BUG=https://github.com/flutter/flutter/issues/4400
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
We now use the `@required` annotation to encourage developers to
explicitly set onPressed and onChanged callbacks to null when that would
disable the widget.
Fixes#287
Also:
* Make PaginatedDataTable able to scroll itself horizontally.
* Make drop down buttons support having an explicit text style and icon
size given.
* Fix a bug with drop-down buttons asserting when opened partly
off-screen.
* Make sure to pop the drop-down button's route if the drop-down button
is discarded while the route is up.
* Remove extraneous padding on drop-down buttons. (Couldn't figure out
why it was there, and it breaks alignment when a drop-down is mixed
with other text.)
* Some docs improvements.
* Add Route.isActive
* Add a setState() method to ModalRoutes.
I was also going to implement sorting and emptying the cart but the
current data model doesn't make that easy, so I gave up on that. That's
why the TODOs are moved around though.
This fix isn't completely statisfying because it has a scaling limit. The ideal
fix would actually viewport the tiles in the grid. However, this fix is much
easier at the moment.
Fixes#4395
Now that there's a new string_scanner in town, we're having dependency
resolution conflict because of flutter_markdown's tight dependency. This
patch loosens the dependency and resolves the conflict.
Although beautiful, having a continuous animation on the front page of the
gallery gives the impression that Flutter burns battery and makes phones hot.
This patch replaces the animation with solid purple. However, we might
eventually want to use a static image.
This demo burns battery continuously even when there's no change to the visual
appearance. This patch removes this demo to avoid giving the impression that
Flutter burns battery.
Related to #4120
This introduces the key parts of a paginated data table, not including
the built-in pagination features.
* Provide more data for the data table demo, so there's data to page.
* Introduce a ChangeNotifier class which abstracts out
addListener/removeListener/notifyListeners. We might be able to use
this to simplify existing classes as well, though this patch doesn't
do that.
* Introduce DataTableSource, a delegate for getting data for data
tables. This will also be used by ScrollingDataTable in due course.
* Introduce PaginatedDataTable, a widget that wraps DataTable and only
shows N rows at a time, fed by a DataTableSource.
