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Fix header not sticking in reverse direction #72

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Fix header not sticking in reverse direction #72

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11a3462
Fix header not sticking in reverse direction
JAicewizard Jan 26, 2023
a3f6cba
Only do layout when needed
JAicewizard Jan 26, 2023
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68 changes: 40 additions & 28 deletions lib/sticky_headers/render.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,8 @@ class RenderStickyHeader extends RenderBox
ScrollPosition _scrollPosition;
bool _overlapHeaders;

double headerHeight = 0.0;

RenderStickyHeader({
required ScrollPosition scrollPosition,
RenderStickyHeaderCallback? callback,
Expand All @@ -47,10 +49,10 @@ class RenderStickyHeader extends RenderBox
}
final ScrollPosition oldValue = _scrollPosition;
_scrollPosition = newValue;
markNeedsLayout();
markNeedsPaint();
if (attached) {
oldValue.removeListener(markNeedsLayout);
newValue.addListener(markNeedsLayout);
oldValue.removeListener(markNeedsPaint);
newValue.addListener(markNeedsPaint);
}
}

Expand All @@ -59,7 +61,7 @@ class RenderStickyHeader extends RenderBox
return;
}
_callback = newValue;
markNeedsLayout();
markNeedsPaint();
}

set overlapHeaders(bool newValue) {
Expand All @@ -73,12 +75,12 @@ class RenderStickyHeader extends RenderBox
@override
void attach(PipelineOwner owner) {
super.attach(owner);
_scrollPosition.addListener(markNeedsLayout);
_scrollPosition.addListener(markNeedsPaint);
}

@override
void detach() {
_scrollPosition.removeListener(markNeedsLayout);
_scrollPosition.removeListener(markNeedsPaint);
super.detach();
}

Expand All @@ -100,39 +102,29 @@ class RenderStickyHeader extends RenderBox
_headerBox.layout(childConstraints, parentUsesSize: true);
_contentBox.layout(childConstraints, parentUsesSize: true);

final headerHeight = roundToNearestPixel(_headerBox.size.height);
headerHeight = roundToNearestPixel(_headerBox.size.height);
final contentHeight = roundToNearestPixel(_contentBox.size.height);

// determine size of ourselves based on content widget
final width = constraints.constrainWidth(
max(constraints.minWidth, _contentBox.size.width),
);
final height = constraints.constrainHeight(
max(constraints.minHeight, _overlapHeaders ? contentHeight : headerHeight + contentHeight),
max(constraints.minHeight,
_overlapHeaders ? contentHeight : headerHeight + contentHeight),
);
size = Size(width, height);

// place content underneath header
final contentParentData = _contentBox.parentData as MultiChildLayoutParentData;
contentParentData.offset = Offset(0.0, _overlapHeaders ? 0.0 : headerHeight);

// determine by how much the header should be stuck to the top
final double stuckOffset = roundToNearestPixel(determineStuckOffset());

// place header over content relative to scroll offset
final double maxOffset = height - headerHeight;
final headerParentData = _headerBox.parentData as MultiChildLayoutParentData;
headerParentData.offset = Offset(0.0, max(0.0, min(-stuckOffset, maxOffset)));

// report to widget how much the header is stuck.
if (_callback != null) {
final stuckAmount = max(min(headerHeight, stuckOffset), -headerHeight) / headerHeight;
_callback!(stuckAmount);
}
final contentParentData =
_contentBox.parentData as MultiChildLayoutParentData;
contentParentData.offset =
Offset(0.0, _overlapHeaders ? 0.0 : headerHeight);
}

double determineStuckOffset() {
final scrollBox = _scrollPosition.context.notificationContext!.findRenderObject();
final scrollBox =
_scrollPosition.context.notificationContext!.findRenderObject();
if (scrollBox?.attached ?? false) {
try {
return localToGlobal(Offset.zero, ancestor: scrollBox).dy;
Expand Down Expand Up @@ -165,14 +157,16 @@ class RenderStickyHeader extends RenderBox
double computeMinIntrinsicHeight(double width) {
return _overlapHeaders
? _contentBox.getMinIntrinsicHeight(width)
: (_headerBox.getMinIntrinsicHeight(width) + _contentBox.getMinIntrinsicHeight(width));
: (_headerBox.getMinIntrinsicHeight(width) +
_contentBox.getMinIntrinsicHeight(width));
}

@override
double computeMaxIntrinsicHeight(double width) {
return _overlapHeaders
? _contentBox.getMaxIntrinsicHeight(width)
: (_headerBox.getMaxIntrinsicHeight(width) + _contentBox.getMaxIntrinsicHeight(width));
: (_headerBox.getMaxIntrinsicHeight(width) +
_contentBox.getMaxIntrinsicHeight(width));
}

@override
Expand All @@ -182,14 +176,32 @@ class RenderStickyHeader extends RenderBox

@override
bool hitTestChildren(HitTestResult result, {required Offset position}) {
return defaultHitTestChildren(result as BoxHitTestResult, position: position);
return defaultHitTestChildren(result as BoxHitTestResult,
position: position);
}

@override
bool get isRepaintBoundary => true;

@override
void paint(PaintingContext context, Offset offset) {
// determine by how much the header should be stuck to the top
final double stuckOffset = roundToNearestPixel(determineStuckOffset());

// place header over content relative to scroll offset
final double maxOffset = size.height - headerHeight;
final headerParentData =
_headerBox.parentData as MultiChildLayoutParentData;
headerParentData.offset =
Offset(0.0, max(0.0, min(-stuckOffset, maxOffset)));

// report to widget how much the header is stuck.
if (_callback != null) {
final stuckAmount =
max(min(headerHeight, stuckOffset), -headerHeight) / headerHeight;
_callback!(stuckAmount);
}

defaultPaint(context, offset);
}
}