Referencing a Control with a String

Question

I have an USB controller, Xk-60 from P.I. Engineering, is configure and working properly. The following code read if a key is pressed on the controller and select a case based on the returned CID value. All good until here. Now a like to refer to several Checkbox dynamically also using the CID value. I don't seem to find the right way ...

This is not valid:

If e.PressState = True And **ctl.Checked** = False Then

Private Sub Xk60_80_1_ButtonChange(ByVal e As XK_60_80.XKeyEventArgs) Handles Xk60_80_1.ButtonChange
    Select Case e.CID
        Case 1001
            Dim nbr As String = e.CID.ToString().Remove(0, 3)
            Dim ctl() As Control = Me.Controls.Find("CheckBox" & nbr, True)
            If e.PressState = True And ctl.Checked = False Then              
                CheckBox1.Checked = True
            ElseIf e.PressState = True And CheckBox1.Checked = True Then
                CheckBox1.Checked = False
            End If
    End Select
End Sub

MatSnow · Accepted Answer · 2018-04-05 14:47:13Z

2

Me.Controls.Find returns an array of controls.
Also Control has no Checked-property so it's better to search only the controls of type CheckBox and use the first found with the appropriate name:

Dim ctl As CheckBox = Me.Controls.OfType(Of CheckBox).
                      First(Function(c) c.Name = "CheckBox" & nbr)

If e.PressState = True AndAlso ctl IsNot Nothing AndAlso ctl.Checked = False Then
    CheckBox1.Checked = True
ElseIf e.PressState = True And CheckBox1.Checked = True Then
    CheckBox1.Checked = False
End If

Also it's better to use short-circuiting like already mentioned in Tim Schmelter's answer.

answered Apr 5, 2018 at 14:47

MatSnow

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3 Comments

Tim Schmelter Over a year ago

This approach has one drawback. Unlike Controls.Find Controls.OfType is not searching for the control recursively. So if it's contained in a child control like a Panel you won't find it.

Alessandro Mandelli Over a year ago

Or cycle i from 0 to ctl.count-1 and set ctl(i).enabled = False

SirAleXbox Over a year ago

Great this works for me. Not searching recursively is a drawback indeed. Thanks you all.

Tim Schmelter · Accepted Answer · 2018-04-05 14:51:14Z

2

Controls.Find returns a Control(), so possibly multiple controls. If you want the first:

Dim checkBoxControl = TryCast(ctl.ElementAtOrDefault(0), CheckBox)

CheckBox1.Checked = e.PressState AndAlso 
                    checkBoxControl IsNot Nothing AndAlso 
                    Not checkBoxControl.Checked

Note that i have used AnsAlso instead of And which is a short-circuiting operator which stops if the previous condition is not met. Otherwise you would get a NullReferenceException at checkBoxControl.Checked if checkBoxControl was already Nothing. So use AndAlso(and OrElse).

edited Apr 5, 2018 at 14:51

answered Apr 5, 2018 at 14:36

Tim Schmelter

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