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Disallow unsafe ancestor methods (#9425)

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This commit is contained in:
Hans Muller 2017-04-17 15:44:41 -07:00 committed by GitHub
parent acd75c0a3b
commit b52d659406
2 changed files with 176 additions and 2 deletions
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56
packages/flutter/lib/src/widgets/framework.dart
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@ -1585,6 +1585,11 @@ abstract class BuildContext {
/// (directly or indirectly) from build methods, layout and paint callbacks, or
/// from [State.didChangeDependencies].
///
/// This method should not be called from [State.deactivate] or [State.dispose]
/// because the element tree is no longer stable at that time. To refer to
/// an ancestor from one of those methods, save a reference to the ancestor
/// in [State.didChangeDependencies].
///
/// It is also possible to call this from interaction event handlers (e.g.
/// gesture callbacks) or timers, to obtain a value once, if that value is not
/// going to be cached and reused later.
@ -1609,6 +1614,11 @@ abstract class BuildContext {
/// widgets to obtain their corresponding [InheritedElement] object so that they
/// can call [InheritedElement.dispatchDidChangeDependencies] to actually
/// notify the widgets that _did_ register such a relationship.
///
/// This method should not be called from [State.deactivate] or [State.dispose]
/// because the element tree is no longer stable at that time. To refer to
/// an ancestor from one of those methods, save a reference to the ancestor
/// by calling [inheritFromWidgetOfExactType] in [State.didChangeDependencies].
InheritedElement ancestorInheritedElementForWidgetOfExactType(Type targetType);
/// Returns the nearest ancestor widget of the given type, which must be the
@ -1623,6 +1633,11 @@ abstract class BuildContext {
/// Calling this method is relatively expensive (O(N) in the depth of the
/// tree). Only call this method if the distance from this widget to the
/// desired ancestor is known to be small and bounded.
///
/// This method should not be called from [State.deactivate] or [State.dispose]
/// because the widget tree is no longer stable at that time. To refer to
/// an ancestor from one of those methods, save a reference to the ancestor
/// by calling [inheritFromWidgetOfExactType] in [State.didChangeDependencies].
Widget ancestorWidgetOfExactType(Type targetType);
/// Returns the [State] object of the nearest ancestor [StatefulWidget] widget
@ -1631,7 +1646,7 @@ abstract class BuildContext {
/// This should not be used from build methods, because the build context will
/// not be rebuilt if the value that would be returned by this method changes.
/// In general, [inheritFromWidgetOfExactType] is more appropriate for such
/// cases. This method is useful to change the state of an ancestor widget in
/// cases. This method is useful for changing the state of an ancestor widget in
/// a one-off manner, for example, to cause an ancestor scrolling list to
/// scroll this build context's widget into view, or to move the focus in
/// response to user interaction.
@ -1645,6 +1660,11 @@ abstract class BuildContext {
/// tree). Only call this method if the distance from this widget to the
/// desired ancestor is known to be small and bounded.
///
/// This method should not be called from [State.deactivate] or [State.dispose]
/// because the widget tree is no longer stable at that time. To refer to
/// an ancestor from one of those methods, save a reference to the ancestor
/// by calling [inheritFromWidgetOfExactType] in [State.didChangeDependencies].
///
/// Example:
///
/// ```dart
@ -1663,6 +1683,11 @@ abstract class BuildContext {
/// it is used by [Material] so that [InkWell] widgets can trigger the ink
/// splash on the [Material]'s actual render object.
///
/// This method should not be called from [State.deactivate] or [State.dispose]
/// because the widget tree is no longer stable at that time. To refer to
/// an ancestor from one of those methods, save a reference to the ancestor
/// by calling [inheritFromWidgetOfExactType] in [State.didChangeDependencies].
///
/// Calling this method is relatively expensive (O(N) in the depth of the
/// tree). Only call this method if the distance from this widget to the
/// desired ancestor is known to be small and bounded.
@ -1677,6 +1702,11 @@ abstract class BuildContext {
/// This is useful for inspecting the widget tree.
///
/// Calling this method is relatively expensive (O(N) in the depth of the tree).
///
/// This method should not be called from [State.deactivate] or [State.dispose]
/// because the element tree is no longer stable at that time. To refer to
/// an ancestor from one of those methods, save a reference to the ancestor
/// by calling [inheritFromWidgetOfExactType] in [State.didChangeDependencies].
void visitAncestorElements(bool visitor(Element element));
/// Walks the children of this widget.
@ -2739,7 +2769,7 @@ abstract class Element implements BuildContext {
'The size of this render object has not yet been determined because '
'this render object has not yet been through layout, which typically '
'means that the size getter was called too early in the pipeline '
'(e.g., during the build pahse) before the framework has determined '
'(e.g., during the build phase) before the framework has determined '
'the size and position of the render objects during layout.\n'
'The size getter was called for the following element:\n'
' $this\n'
@ -2756,8 +2786,25 @@ abstract class Element implements BuildContext {
Set<InheritedElement> _dependencies;
bool _hadUnsatisfiedDependencies = false;
bool _debugCheckStateIsActiveForAncestorLoopkup() {
assert(() {
if (_debugLifecycleState != _ElementLifecycle.active) {
throw new FlutterError(
'Looking up a deactivated widget\'s ancestor is unsafe.\n'
'At this point the state of the widget\'s element tree is no longer '
'stable. To safely refer to a widget\'s ancestor in its dispose() method, '
'save a reference to the ancestor by calling inheritFromWidgetOfExactType() '
'in the widget\'s didChangeDependencies() method.\n'
);
}
return true;
});
return true;
}
@override
InheritedWidget inheritFromWidgetOfExactType(Type targetType) {
assert(_debugCheckStateIsActiveForAncestorLoopkup);
final InheritedElement ancestor = _inheritedWidgets == null ? null : _inheritedWidgets[targetType];
if (ancestor != null) {
assert(ancestor is InheritedElement);
@ -2772,6 +2819,7 @@ abstract class Element implements BuildContext {
@override
InheritedElement ancestorInheritedElementForWidgetOfExactType(Type targetType) {
assert(_debugCheckStateIsActiveForAncestorLoopkup);
final InheritedElement ancestor = _inheritedWidgets == null ? null : _inheritedWidgets[targetType];
return ancestor;
}
@ -2783,6 +2831,7 @@ abstract class Element implements BuildContext {
@override
Widget ancestorWidgetOfExactType(Type targetType) {
assert(_debugCheckStateIsActiveForAncestorLoopkup);
Element ancestor = _parent;
while (ancestor != null && ancestor.widget.runtimeType != targetType)
ancestor = ancestor._parent;
@ -2791,6 +2840,7 @@ abstract class Element implements BuildContext {
@override
State ancestorStateOfType(TypeMatcher matcher) {
assert(_debugCheckStateIsActiveForAncestorLoopkup);
Element ancestor = _parent;
while (ancestor != null) {
if (ancestor is StatefulElement && matcher.check(ancestor.state))
@ -2803,6 +2853,7 @@ abstract class Element implements BuildContext {
@override
RenderObject ancestorRenderObjectOfType(TypeMatcher matcher) {
assert(_debugCheckStateIsActiveForAncestorLoopkup);
Element ancestor = _parent;
while (ancestor != null) {
if (ancestor is RenderObjectElement && matcher.check(ancestor.renderObject))
@ -2815,6 +2866,7 @@ abstract class Element implements BuildContext {
@override
void visitAncestorElements(bool visitor(Element element)) {
assert(_debugCheckStateIsActiveForAncestorLoopkup);
Element ancestor = _parent;
while (ancestor != null && visitor(ancestor))
ancestor = ancestor._parent;

122
packages/flutter/test/widgets/dispose_ancestor_lookup_test.dart Normal file
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@ -0,0 +1,122 @@
// 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 'package:flutter_test/flutter_test.dart' hide TypeMatcher;
import 'package:flutter/widgets.dart';
typedef void TestCallback(BuildContext context);
class TestWidget extends StatefulWidget {
TestWidget(this.callback);
final TestCallback callback;
@override
TestWidgetState createState() => new TestWidgetState();
}
class TestWidgetState extends State<TestWidget> {
@override
void dispose() {
widget.callback(context);
super.dispose();
}
@override
Widget build(BuildContext context) => const Text('test');
}
void main() {
testWidgets('inheritFromWidgetOfExactType() called from dispose() throws error', (WidgetTester tester) async {
bool disposeCalled = false;
await tester.pumpWidget(
new TestWidget((BuildContext context) {
disposeCalled = true;
context.inheritFromWidgetOfExactType(Container);
}),
);
await tester.pumpWidget(new Container());
expect(disposeCalled, isTrue);
expect(tester.takeException(), isFlutterError);
});
testWidgets('ancestorInheritedElementForWidgetOfExactType() called from dispose() throws error', (WidgetTester tester) async {
bool disposeCalled = false;
await tester.pumpWidget(
new TestWidget((BuildContext context) {
disposeCalled = true;
context.ancestorInheritedElementForWidgetOfExactType(Container);
}),
);
await tester.pumpWidget(new Container());
expect(disposeCalled, isTrue);
expect(tester.takeException(), isFlutterError);
});
testWidgets('ancestorWidgetOfExactType() called from dispose() throws error', (WidgetTester tester) async {
bool disposeCalled = false;
await tester.pumpWidget(
new TestWidget((BuildContext context) {
disposeCalled = true;
context.ancestorWidgetOfExactType(Container);
}),
);
await tester.pumpWidget(new Container());
expect(disposeCalled, isTrue);
expect(tester.takeException(), isFlutterError);
});
testWidgets('ancestorStateOfType() called from dispose() throws error', (WidgetTester tester) async {
bool disposeCalled = false;
await tester.pumpWidget(
new TestWidget((BuildContext context) {
disposeCalled = true;
context.ancestorStateOfType(const TypeMatcher<Container>());
}),
);
await tester.pumpWidget(new Container());
expect(disposeCalled, isTrue);
expect(tester.takeException(), isFlutterError);
});
testWidgets('ancestorRenderObjectOfType() called from dispose() throws error', (WidgetTester tester) async {
bool disposeCalled = false;
await tester.pumpWidget(
new TestWidget((BuildContext context) {
disposeCalled = true;
context.ancestorRenderObjectOfType(const TypeMatcher<Container>());
}),
);
await tester.pumpWidget(new Container());
expect(disposeCalled, isTrue);
expect(tester.takeException(), isFlutterError);
});
testWidgets('visitAncestorElements() called from dispose() throws error', (WidgetTester tester) async {
bool disposeCalled = false;
await tester.pumpWidget(
new TestWidget((BuildContext context) {
disposeCalled = true;
context.visitAncestorElements((Element element){ });
}),
);
await tester.pumpWidget(new Container());
expect(disposeCalled, isTrue);
expect(tester.takeException(), isFlutterError);
});
testWidgets('dispose() method does not unconditionally throw an error', (WidgetTester tester) async {
bool disposeCalled = false;
await tester.pumpWidget(
new TestWidget((BuildContext context) {
disposeCalled = true;
}),
);
await tester.pumpWidget(new Container());
expect(disposeCalled, isTrue);
});
}