void EnsureRowsColumnsInitialized() { _columns = ColumnDefinitions == null ? new List <ColumnDefinition>() : ColumnDefinitions.ToList(); _rows = RowDefinitions == null ? new List <RowDefinition>() : RowDefinitions.ToList(); int lastRow = -1; for (var index = 0; index < InternalChildren.Count; index++) { Element w = InternalChildren[index]; lastRow = Math.Max(lastRow, GetRow(w) + GetRowSpan(w) - 1); } lastRow = Math.Max(lastRow, RowDefinitions.Count - 1); int lastCol = -1; for (var index = 0; index < InternalChildren.Count; index++) { Element w = InternalChildren[index]; lastCol = Math.Max(lastCol, GetColumn(w) + GetColumnSpan(w) - 1); } lastCol = Math.Max(lastCol, ColumnDefinitions.Count - 1); while (_columns.Count <= lastCol) { _columns.Add(new ColumnDefinition()); } while (_rows.Count <= lastRow) { _rows.Add(new RowDefinition()); } for (var index = 0; index < _columns.Count; index++) { ColumnDefinition col = _columns[index]; col.ActualWidth = -1; } for (var index = 0; index < _rows.Count; index++) { RowDefinition row = _rows[index]; row.ActualHeight = -1; } }