vb.net图表控制点onclick事件

Question

Hello i am trying to add a click event to chart points but i am getting the following Error when i click the chart "Object reference not set to an instance of an object"

here is my code

Private Sub Chart1_Click(sender As Object, e As System.EventArgs) Handles Chart1.Click
    Try
        Dim pointindex As Integer
        If result.ChartElementType = ChartElementType.DataPoint Then
            pointindex = result.PointIndex
        End If
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try
End Sub

Private Sub Form1_MouseDown(sender As Object, e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseDown
    result = Chart1.HitTest(e.X, e.Y)
End Sub

Answer 1

If the mouse cursor is above a control only the control will receive events but not the form (for workarounds see eg this question: Winforms : Intercepting Mouse Event on Main Form first, not on Controls ).

So Form1_MouseDown will not fire and result will still be Nothing in Chart1_Click .

A workaround could look like this:

Private Sub Chart1_Click(sender As Object, e As System.EventArgs) Handles Chart1.Click
    Try
        Dim pointindex As Integer
        Dim result As HitTestResult
        result = Chart1.HitTest(Cursor.Position.X, Cursor.Position.Y)
        If result.ChartElementType = ChartElementType.DataPoint Then
            pointindex = result.PointIndex
        End If
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try
End Sub