double GetAverageElementSize(
Size availableSize,
VirtualizingLayoutContext context,
StackLayoutState stackLayoutState)
{
double averageElementSize = 0;
if (context.ItemCount > 0)
{
if (stackLayoutState.TotalElementsMeasured == 0)
{
var tmpElement = context.GetOrCreateElementAt(0, ElementRealizationOptions.ForceCreate | ElementRealizationOptions.SuppressAutoRecycle);
stackLayoutState.FlowAlgorithm.MeasureElement(tmpElement, 0, availableSize, context);
context.RecycleElement(tmpElement);
}
MUX_ASSERT(stackLayoutState.TotalElementsMeasured > 0);
averageElementSize = Math.Round(stackLayoutState.TotalElementSize / stackLayoutState.TotalElementsMeasured);
}
return(averageElementSize);
}
protected internal override void InitializeForContextCore(VirtualizingLayoutContext context)
{
var state = context.LayoutState;
StackLayoutState stackState = default;
if (state != null)
{
stackState = GetAsStackState(state);
}
if (stackState == null)
{
if (state != null)
{
throw new InvalidOperationException("LayoutState must derive from StackLayoutState.");
}
// Custom deriving layouts could potentially be stateful.
// If that is the case, we will just create the base state required by UniformGridLayout ourselves.
stackState = new StackLayoutState();
}
stackState.InitializeForContext(context, this);
}
