protected override void performLayout()
{
this.childManager.didStartLayout();
this.childManager.setDidUnderflow(false);
float scrollOffset = this.constraints.scrollOffset + this.constraints.cacheOrigin;
D.assert(scrollOffset >= 0.0f);
float remainingExtent = this.constraints.remainingCacheExtent;
D.assert(remainingExtent >= 0.0f);
float targetEndScrollOffset = scrollOffset + remainingExtent;
SliverGridLayout layout = this._gridDelegate.getLayout(this.constraints);
int firstIndex = layout.getMinChildIndexForScrollOffset(scrollOffset);
int?targetLastIndex = targetEndScrollOffset.isFinite()
? (int?)layout.getMaxChildIndexForScrollOffset(targetEndScrollOffset)
: null;
if (this.firstChild != null)
{
int oldFirstIndex = this.indexOf(this.firstChild);
int oldLastIndex = this.indexOf(this.lastChild);
int leadingGarbage = (firstIndex - oldFirstIndex).clamp(0, this.childCount);
int trailingGarbage = targetLastIndex == null
? 0
: ((oldLastIndex - targetLastIndex) ?? 0).clamp(0, this.childCount);
this.collectGarbage(leadingGarbage, trailingGarbage);
}
else
{
this.collectGarbage(0, 0);
}
SliverGridGeometry firstChildGridGeometry = layout.getGeometryForChildIndex(firstIndex);
float?leadingScrollOffset = firstChildGridGeometry.scrollOffset;
float?trailingScrollOffset = firstChildGridGeometry.trailingScrollOffset;
if (this.firstChild == null)
{
if (!this.addInitialChild(index: firstIndex,
layoutOffset: firstChildGridGeometry.scrollOffset ?? 0.0f))
{
float max = layout.computeMaxScrollOffset(this.childManager.childCount ?? 0);
this.geometry = new SliverGeometry(
scrollExtent: max,
maxPaintExtent: max
);
this.childManager.didFinishLayout();
return;
}
}
RenderBox trailingChildWithLayout = null;
for (int index = this.indexOf(this.firstChild) - 1; index >= firstIndex; --index)
{
SliverGridGeometry gridGeometry = layout.getGeometryForChildIndex(index);
RenderBox child = this.insertAndLayoutLeadingChild(
gridGeometry.getBoxConstraints(this.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)
{
this.firstChild.layout(firstChildGridGeometry.getBoxConstraints(this.constraints));
SliverGridParentData childParentData = this.firstChild.parentData as SliverGridParentData;
childParentData.layoutOffset = firstChildGridGeometry.scrollOffset ?? 0.0f;
childParentData.crossAxisOffset = firstChildGridGeometry.crossAxisOffset ?? 0.0f;
trailingChildWithLayout = this.firstChild;
}
for (int index = this.indexOf(trailingChildWithLayout) + 1;
targetLastIndex == null || index <= targetLastIndex;
++index)
{
SliverGridGeometry gridGeometry = layout.getGeometryForChildIndex(index);
BoxConstraints childConstraints = gridGeometry.getBoxConstraints(this.constraints);
RenderBox child = this.childAfter(trailingChildWithLayout);
if (child == null)
{
child = this.insertAndLayoutChild(childConstraints, after: trailingChildWithLayout);
if (child == null)
{
break;
}
}
else
{
child.layout(childConstraints);
}
trailingChildWithLayout = child;
D.assert(child != null);
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 = this.indexOf(this.lastChild);
D.assert(this.childScrollOffset(this.firstChild) <= scrollOffset);
D.assert(this.debugAssertChildListIsNonEmptyAndContiguous());
D.assert(this.indexOf(this.firstChild) == firstIndex);
D.assert(targetLastIndex == null || lastIndex <= targetLastIndex);
float estimatedTotalExtent = this.childManager.estimateMaxScrollOffset(this.constraints,
firstIndex: firstIndex,
lastIndex: lastIndex,
leadingScrollOffset: leadingScrollOffset ?? 0.0f,
trailingScrollOffset: trailingScrollOffset ?? 0.0f
);
float paintExtent = this.calculatePaintOffset(this.constraints,
from: leadingScrollOffset ?? 0.0f,
to: trailingScrollOffset ?? 0.0f
);
float cacheExtent = this.calculateCacheOffset(this.constraints,
from: leadingScrollOffset ?? 0.0f,
to: trailingScrollOffset ?? 0.0f
);
this.geometry = new SliverGeometry(
scrollExtent: estimatedTotalExtent,
paintExtent: paintExtent,
maxPaintExtent: estimatedTotalExtent,
cacheExtent: cacheExtent,
hasVisualOverflow: true
);
if (estimatedTotalExtent == trailingScrollOffset)
{
this.childManager.setDidUnderflow(true);
}
this.childManager.didFinishLayout();
}
public override float childCrossAxisPosition(RenderObject child)
{
SliverGridParentData childParentData = (SliverGridParentData)child.parentData;
return(childParentData.crossAxisOffset);
}