Matrix With CheckBox

Hi To All,

I had a matrix in my screen..It contains a Item Column and Choose Column...In that Choose Column in CheckBox column..There is a SelectAll button in my screen..If i click the SelectAll Button all the Checkbox should be checked atonce. But for me, all the checkbox had checked one by one...If i am having minimum number of rows means its ok...If the row exceeds 20 to 25 means, i shd wait till all the checkbox got checked......My need is all my checkbox shd be checked atonce..How to do it...Here is my source....

Case SAPbouiCOM.BoEventTypes.et_CLICK
If pVal.ItemUID = "SelectAll" And pVal.BeforeAction = False Then
For intCount As Integer = 1 To MatMName.VisualRowCount
Try
MatMName.GetLineData(intCount)
MatMName = Conv_Form.Items.Item("MatMName").Specific
MatMName.Columns.Item("Choose").Cells.Item(intCount).Click(SAPbouiCOM.BoCellClickType.ct_Regular)
Catch ex As Exception
End Try
Next
End If