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Ensure that SemanticDebugger shows SemanticTree changes from last frame (#10573)

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* Ensure that SemanticDebugger shows SemanticTree changes from last frame

Fixes https://github.com/flutter/flutter/issues/10566

* Comment for clearification
This commit is contained in:
Michael Goderbauer 2017-06-08 15:25:22 -07:00 committed by GitHub
parent 95544383ef
commit 285ab18dde
1 changed files with 8 additions and 2 deletions
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10
packages/flutter/lib/src/widgets/semantics_debugger.dart
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@ -65,8 +65,13 @@ class _SemanticsDebuggerState extends State<SemanticsDebugger> with WidgetsBindi
void _update() {
SchedulerBinding.instance.addPostFrameCallback((Duration timeStamp) {
// We want the update to take effect next frame, so to make that
// explicit we call setState() in a post-frame callback.
// Semantic information are only available at the end of a frame and our
// only chance to paint them on the screen is the next frame. To achieve
// this, we call setState() in a post-frame callback. THIS PATTERN SHOULD
// NOT BE COPIED. Calling setState() in a post-frame callback is a bad
// idea as it will not schedule a frame and your app may be lagging behind
// by one frame. We manually call scheduleFrame() to force a frame and
// ensure that the semantic information are always painted on the screen.
if (mounted) {
// If we got disposed this frame, we will still get an update,
// because the inactive list is flushed after the semantics updates
@ -74,6 +79,7 @@ class _SemanticsDebuggerState extends State<SemanticsDebugger> with WidgetsBindi
setState(() {
// The generation of the _SemanticsDebuggerListener has changed.
});
SchedulerBinding.instance.scheduleFrame();
}
});
}