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Fix padding on infinite scrolling list

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Rather than using a Padding widget to provide padding along the scrolling axis,
we now just figure the padding into where we draw the items. This patch fixes
an issue where we would remove the first topmost item in a scrollable list too
early because we thought it was already off screen.

Fixes #697
This commit is contained in:
Adam Barth 2015-08-19 18:01:02 -07:00
parent 87adaf3fe9
commit 72807ef8ec
1 changed files with 33 additions and 13 deletions
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46
packages/flutter/lib/widgets/scrollable.dart
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@ -384,14 +384,30 @@ abstract class FixedHeightScrollable extends Scrollable {
});
}
double get _leadingPadding {
if (scrollDirection == ScrollDirection.vertical)
return padding.top;
return padding.left;
}
double get _trailingPadding {
if (scrollDirection == ScrollDirection.vertical)
return padding.bottom;
return padding.right;
}
EdgeDims get _crossAxisPadding {
if (padding == null)
return null;
if (scrollDirection == ScrollDirection.vertical)
return new EdgeDims.only(left: padding.left, right: padding.right);
return new EdgeDims.only(top: padding.top, bottom: padding.bottom);
}
void _updateContentsExtent() {
double contentsExtent = itemExtent * itemCount;
if (padding != null) {
if (scrollDirection == ScrollDirection.vertical)
contentsExtent += padding.top + padding.bottom;
else
contentsExtent += padding.left + padding.right;
}
if (padding != null)
contentsExtent += _leadingPadding + _trailingPadding;
scrollBehavior.contentsSize = contentsExtent;
}
@ -413,25 +429,29 @@ abstract class FixedHeightScrollable extends Scrollable {
_updateScrollOffset();
}
double paddedScrollOffset = scrollOffset;
if (padding != null)
paddedScrollOffset -= _leadingPadding;
int itemShowIndex = 0;
int itemShowCount = 0;
Offset viewportOffset = Offset.zero;
if (_containerExtent != null && _containerExtent > 0.0) {
if (scrollOffset < 0.0) {
double visibleHeight = _containerExtent + scrollOffset;
if (paddedScrollOffset < 0.0) {
double visibleHeight = _containerExtent + paddedScrollOffset;
itemShowCount = (visibleHeight / itemExtent).round() + 1;
viewportOffset = _toOffset(scrollOffset);
viewportOffset = _toOffset(paddedScrollOffset);
} else {
itemShowCount = (_containerExtent / itemExtent).ceil();
double alignmentDelta = -scrollOffset % itemExtent;
double alignmentDelta = -paddedScrollOffset % itemExtent;
double drawStart;
if (alignmentDelta != 0.0) {
alignmentDelta -= itemExtent;
itemShowCount += 1;
drawStart = scrollOffset + alignmentDelta;
drawStart = paddedScrollOffset + alignmentDelta;
viewportOffset = _toOffset(-alignmentDelta);
} else {
drawStart = scrollOffset;
drawStart = paddedScrollOffset;
}
itemShowIndex = math.max(0, (drawStart / itemExtent).floor());
}
@ -453,7 +473,7 @@ abstract class FixedHeightScrollable extends Scrollable {
scrollDirection: scrollDirection,
scrollOffset: viewportOffset,
child: new Container(
padding: padding,
padding: _crossAxisPadding,
child: new Block(items, direction: blockDirection)
)
)