vb.net chart control point onclick event

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

My guess is that the form does not receive the mouse down event so result is not set leading to the error mentioned. This is something you can easily check with a breakpoint or debug output. If that really is the problem you can use `Cursor.Position` in `Chart1_Click`. — Paul B., Jul 16 '12 at 06:58
Great. I'll post a more descriptive answer for future reference. — Paul B., Jul 16 '12 at 14:33

score 1 · Accepted Answer · edited May 23 '17 at 12:17

If the mouse cursor is above a control only the control will receive events but not the form (for workarounds see e.g. 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

vb.net chart control point onclick event

1 Answers1