Xamarin CollectionView Binding Visible not shown

The behavior of the UICollectionViewFlowLayout is not defined because:
the item width must be less than the width of the UICollectionView minus the section insets left and right values, minus the content insets left and right values.
Make a symbolic breakpoint at UICollectionViewFlowLayoutBreakForInvalidSizes to catch this in the debugger.

ItemSizingStrategy="MeasureFirstItem" or ItemSizingStrategy="MeasureAllItems" 아이템 size 지정

CollectionView 바인딩 item 안보임 Colleciton item 중 일부 Size null 일때.. 첫번째 아이템 사이즈로 Measure 하자.