protected override void performLayout()
{
SliverConstraints constraints = this.constraints;
D.assert(constraints.axisDirection == AxisDirection.down);
D.assert(constraints.growthDirection == GrowthDirection.forward);
float layoutExtent =
(_hasLayoutExtent ? 1.0f : 0.0f) * _refreshIndicatorExtent;
if (layoutExtent != layoutExtentOffsetCompensation)
{
geometry = new SliverGeometry(
scrollOffsetCorrection: layoutExtent - layoutExtentOffsetCompensation
);
layoutExtentOffsetCompensation = layoutExtent;
}
bool active = constraints.overlap <0.0 || layoutExtent> 0.0;
float overscrolledExtent =
constraints.overlap < 0.0f ? constraints.overlap.abs() : 0.0f;
child.layout(
constraints.asBoxConstraints(
maxExtent: layoutExtent + overscrolledExtent
),
parentUsesSize: true
);
if (active)
{
geometry = new SliverGeometry(
scrollExtent: layoutExtent,
paintOrigin: -overscrolledExtent - constraints.scrollOffset,
paintExtent: Mathf.Max(
Mathf.Max(child.size.height, layoutExtent) - constraints.scrollOffset, 0.0f),
maxPaintExtent: Mathf.Max(
Mathf.Max(child.size.height, layoutExtent) - constraints.scrollOffset, 0.0f),
layoutExtent: Mathf.Max(layoutExtent - constraints.scrollOffset, 0.0f));
}
else
{
geometry = SliverGeometry.zero;
}
}
protected override void performLayout()
{
childManager.didStartLayout();
childManager.setDidUnderflow(false);
float scrollOffset = constraints.scrollOffset + constraints.cacheOrigin;
D.assert(scrollOffset >= 0.0f);
float remainingExtent = constraints.remainingCacheExtent;
D.assert(remainingExtent >= 0.0f);
float targetEndScrollOffset = scrollOffset + remainingExtent;
SliverGridLayout layout = _gridDelegate.getLayout(constraints);
int firstIndex = layout.getMinChildIndexForScrollOffset(scrollOffset);
int?targetLastIndex = targetEndScrollOffset.isFinite()
? (int?)layout.getMaxChildIndexForScrollOffset(targetEndScrollOffset)
: null;
if (firstChild != null)
{
int oldFirstIndex = indexOf(firstChild);
int oldLastIndex = indexOf(lastChild);
int leadingGarbage = (firstIndex - oldFirstIndex).clamp(0, childCount);
int trailingGarbage = targetLastIndex == null
? 0
: ((oldLastIndex - targetLastIndex) ?? 0).clamp(0, childCount);
collectGarbage(leadingGarbage, trailingGarbage);
}
else
{
collectGarbage(0, 0);
}
SliverGridGeometry firstChildGridGeometry = layout.getGeometryForChildIndex(firstIndex);
float?leadingScrollOffset = firstChildGridGeometry.scrollOffset;
float?trailingScrollOffset = firstChildGridGeometry.trailingScrollOffset;
if (firstChild == null)
{
if (!addInitialChild(index: firstIndex,
layoutOffset: firstChildGridGeometry.scrollOffset ?? 0.0f))
{
float max = layout.computeMaxScrollOffset(childManager.childCount ?? 0);
geometry = new SliverGeometry(
scrollExtent: max,
maxPaintExtent: max
);
childManager.didFinishLayout();
return;
}
}
RenderBox trailingChildWithLayout = null;
for (int index = indexOf(firstChild) - 1; index >= firstIndex; --index)
{
SliverGridGeometry gridGeometry = layout.getGeometryForChildIndex(index);
RenderBox child = insertAndLayoutLeadingChild(
gridGeometry.getBoxConstraints(constraints)
);
SliverGridParentData childParentData = child.parentData as SliverGridParentData;
childParentData.layoutOffset = gridGeometry.scrollOffset ?? 0.0f;
childParentData.crossAxisOffset = gridGeometry.crossAxisOffset ?? 0.0f;
D.assert(childParentData.index == index);
trailingChildWithLayout = trailingChildWithLayout ?? child;
trailingScrollOffset =
Mathf.Max(trailingScrollOffset ?? 0.0f, gridGeometry.trailingScrollOffset ?? 0.0f);
}
if (trailingChildWithLayout == null)
{
firstChild.layout(firstChildGridGeometry.getBoxConstraints(constraints));
SliverGridParentData childParentData = firstChild.parentData as SliverGridParentData;
childParentData.layoutOffset = firstChildGridGeometry.scrollOffset ?? 0.0f;
childParentData.crossAxisOffset = firstChildGridGeometry.crossAxisOffset ?? 0.0f;
trailingChildWithLayout = firstChild;
}
for (int index = indexOf(trailingChildWithLayout) + 1;
targetLastIndex == null || index <= targetLastIndex;
++index)
{
SliverGridGeometry gridGeometry = layout.getGeometryForChildIndex(index);
BoxConstraints childConstraints = gridGeometry.getBoxConstraints(constraints);
RenderBox child = childAfter(trailingChildWithLayout);
if (child == null || indexOf(child) != index)
{
child = insertAndLayoutChild(childConstraints, after: trailingChildWithLayout);
if (child == null)
{
break;
}
}
else
{
child.layout(childConstraints);
}
trailingChildWithLayout = child;
SliverGridParentData childParentData = child.parentData as SliverGridParentData;
childParentData.layoutOffset = gridGeometry.scrollOffset ?? 0.0f;
childParentData.crossAxisOffset = gridGeometry.crossAxisOffset ?? 0.0f;
D.assert(childParentData.index == index);
trailingScrollOffset =
Mathf.Max(trailingScrollOffset ?? 0.0f, gridGeometry.trailingScrollOffset ?? 0.0f);
}
int lastIndex = indexOf(lastChild);
D.assert(childScrollOffset(firstChild) <= scrollOffset);
D.assert(debugAssertChildListIsNonEmptyAndContiguous());
D.assert(indexOf(firstChild) == firstIndex);
D.assert(targetLastIndex == null || lastIndex <= targetLastIndex);
float estimatedTotalExtent = childManager.estimateMaxScrollOffset(
constraints,
firstIndex: firstIndex,
lastIndex: lastIndex,
leadingScrollOffset: leadingScrollOffset ?? 0.0f,
trailingScrollOffset: trailingScrollOffset ?? 0.0f
);
float paintExtent = calculatePaintOffset(
constraints,
from: leadingScrollOffset ?? 0.0f,
to: trailingScrollOffset ?? 0.0f
);
float cacheExtent = calculateCacheOffset(
constraints,
from: leadingScrollOffset ?? 0.0f,
to: trailingScrollOffset ?? 0.0f
);
geometry = new SliverGeometry(
scrollExtent: estimatedTotalExtent,
paintExtent: paintExtent,
maxPaintExtent: estimatedTotalExtent,
cacheExtent: cacheExtent,
hasVisualOverflow: true
);
if (estimatedTotalExtent == trailingScrollOffset)
{
childManager.setDidUnderflow(true);
}
childManager.didFinishLayout();
}