is there a way to know ui element is visible in the scroll view?

myself fix this question, first: Get the count to show in the scroll view.

 private int CalculateCurElementShowCount()
 {
     float offsetCellX = 10.0f;
     float offsetCellY = 10.0f;

     ColumnElementCount = -1;
     RowElementCount = -1;

     if (UI_GridGroup.constraint == GridLayoutGroup.Constraint.FixedColumnCount)
     {
         ColumnElementCount = UI_GridGroup.constraintCount;
     }
     else if(UI_GridGroup.constraint == GridLayoutGroup.Constraint.FixedRowCount)
     {
         RowElementCount = UI_GridGroup.constraintCount;
     }
     
     if(ColumnElementCount == -1)
     {
         ColumnElementCount = (int)( (rectComponent.rect.width + offsetCellX)/(UI_GridGroup.cellSize.x + UI_GridGroup.spacing.x) );
     }
     if(RowElementCount == -1)
     {
         RowElementCount = (int)( (rectComponent.rect.height + offsetCellY) / (UI_GridGroup.cellSize.y + UI_GridGroup.spacing.y) );
     }

     int Count = ColumnElementCount * RowElementCount;
     if(Count < 0)
     {
         Count = 0;
     }

     return Count;
 }

second:

 float showPercent = 1 - ScrollRectConl.verticalNormalizedPosition;
 int centerIndex = (int)(CurAssetList.Count * showPercent);
 int halfOffsetIndex = (int)(ScrollShowCount / 2.0f);

     downloadLogoStartIndex = ((centerIndex + halfOffsetIndex) >= CurAssetList.Count) ? (centerIndex - ScrollShowCount - ColumnElementCount) : (centerIndex - halfOffsetIndex - ColumnElementCount);
     downloadLogoEndIndex = (centerIndex < halfOffsetIndex) ? (centerIndex + ScrollShowCount + ColumnElementCount) : (centerIndex + halfOffsetIndex + ColumnElementCount);

     if (downloadLogoStartIndex < 0)
     {
         downloadLogoStartIndex = 0;
     }

     if (downloadLogoEndIndex >= CurAssetList.Count)
     {
         downloadLogoEndIndex = CurAssetList.Count - 1;
     }