firka/flutter
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Fix a bug where ScrollableGrid/ScrollableList would flicker when (#4794)

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navigating away.

Details are in the bug, but when we navigate away, the overscroll
indicator around the Scrollable would change the widget hierarchy. This
would trigger the Scrollable to rebuild, which would cause its
scrollOffset to be clamped to 0 for a frame.

BUG=https://github.com/flutter/flutter/issues/4597
This commit is contained in:
Matt Perry 2016-06-30 15:43:47 -04:00 committed by GitHub
parent f410ca80b7
commit 6298a1aeb1
3 changed files with 13 additions and 9 deletions
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6
packages/flutter/lib/src/material/overscroll_indicator.dart
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@ -226,10 +226,10 @@ class _OverscrollIndicatorState extends State<OverscrollIndicator> {
child: new AnimatedBuilder( child: new AnimatedBuilder(
animation: _extentAnimation, animation: _extentAnimation,
builder: (BuildContext context, Widget child) { builder: (BuildContext context, Widget child) {
if (_scrollDirection == null) // Haven't seen a scroll yet. // We keep the same widget hierarchy here, even when we're not
return child; // painting anything, to avoid rebuilding the children.
return new CustomPaint( return new CustomPaint(
foregroundPainter: new _Painter( foregroundPainter: _scrollDirection == null ? null : new _Painter(
scrollDirection: _scrollDirection, scrollDirection: _scrollDirection,
extent: _extentAnimation.value, extent: _extentAnimation.value,
isLeading: _scrollOffset < _minScrollOffset, isLeading: _scrollOffset < _minScrollOffset,

4
packages/flutter/lib/src/rendering/proxy_box.dart
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@ -1610,8 +1610,8 @@ class RenderCustomPaint extends RenderProxyBox {
markNeedsPaint(); markNeedsPaint();
} }
if (attached) { if (attached) {
oldPainter._repaint?.removeListener(markNeedsPaint); oldPainter?._repaint?.removeListener(markNeedsPaint);
newPainter._repaint?.addListener(markNeedsPaint); newPainter?._repaint?.addListener(markNeedsPaint);
} }
} }

12
packages/flutter/lib/src/widgets/clamp_overscrolls.dart
View File

@ -50,14 +50,18 @@ class ClampOverscrolls extends InheritedWidget {
/// ///
/// This utility function is typically used by [Scrollable.builder] callbacks. /// This utility function is typically used by [Scrollable.builder] callbacks.
static Widget buildViewport(BuildContext context, ScrollableState state, ViewportBuilder builder) { static Widget buildViewport(BuildContext context, ScrollableState state, ViewportBuilder builder) {
// TODO(ianh): minScrollOffset and maxScrollOffset are typically determined
// by the container and content size. But we don't know those until we
// layout the viewport, which happens after build phase. We need to rethink
// this.
final bool clampOverscrolls = ClampOverscrolls.of(context); final bool clampOverscrolls = ClampOverscrolls.of(context);
final double clampedScrollOffset = clampOverscrolls final double clampedScrollOffset = clampOverscrolls
? state.scrollOffset.clamp(state.scrollBehavior.minScrollOffset, state.scrollBehavior.maxScrollOffset) ? state.scrollOffset.clamp(state.scrollBehavior.minScrollOffset, state.scrollBehavior.maxScrollOffset)
: state.scrollOffset; : state.scrollOffset;
Widget viewport = builder(context, state, clampedScrollOffset); Widget viewport = builder(context, state, clampedScrollOffset);
if (clampOverscrolls) if (clampOverscrolls)
viewport = new ClampOverscrolls(value: false, child: viewport); viewport = new ClampOverscrolls(value: false, child: viewport);
return viewport; return viewport;
} }
@override @override