nullreferenceexception在GridView中點擊標題時

Question

在我的DataGridView中selectionChange中有這樣的代碼，所以當行改變時texbox也發生了變化。下面的代碼工作，我點擊行，它顯示正確，也當我按上/下箭頭。我的問題是，當我點擊網格的Header somwhere時，我有這個nullreferenceexception錯誤Object reference not set to an instance of an object.。我不知道如何處理它，因爲我知道它會返回什麼。

Private Sub DataGridView1_SelectionChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DataGridView1.SelectionChanged 
    Dim index As Integer 
    index = DataGridView1.CurrentCell.RowIndex '<<<<--problem here when I click the header 
    If (index <= maxrows - 1) Or (index <> Nothing) Then 
     TextBox2.Text = DataGridView1.Item(1, index).Value() 
     TextBox3.Text = DataGridView1.Item(2, index).Value() 
     TextBox4.Text = DataGridView1.Item(3, index).Value() 
    End If 
End Sub 

Answer 1

無論何時獲取RowIndex時都會引發null引用，其中沒有選擇ROW。
單擊標題調用SORT，這將清除選擇。
這將幫助你擺脫nullreference異常

If DatagridView1.SelectedRows.Count = 0 Then 
     Msgbox "Nothing Selected" 
     Exit Sub 'Trapping 
    End If 

代碼：

Private Sub DataGridView1_SelectionChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DataGridView1.SelectionChanged 
    If DatagridView1.SelectedRows.Count = 0 Then 
     Msgbox "Nothing Selected" 
     Exit Sub 'Trapping 
    End If 

    Dim index As Integer 
    With DataGridView 
     index = .CurrentRow.RowIndex 
     If (index <= maxrows - 1) Then 
      TextBox2.Text = .Item(1, index).Value() 
      TextBox3.Text = .Item(2, index).Value() 
      TextBox4.Text = .Item(3, index).Value() 
     End If 
    End With 
End Sub