Using sender as a case in Select Case Statement

Question

When my form loads it adds some handles (using AddHandler) to a sub (showStatus). What this sub does is checks which control activated the sub (using sender.Equals) and displays text in the status label (status) accordingly.

For this I use an If...Then statement for each possibility. There are many possibilities and my code get cluttered. Is there a way to do the same thing with a Select...Case statement. I tried:

        Select Case sender
            Case tbOne : status.Text = "blahblahblahblahblahblah"
        End Select

where: tbOne is a textbox, status is a StatusLabel

It gives me an error though, saying "Operator '=' is not defined for types 'Object' and 'System.Windows.Forms.TextBox'."

Any ideas on how I can get this to work with a select case statement?

Answer 1

 

Dim s as string = directcast(sender,textbox).text

select case s

case allthecases

 end select

 

Answer 2

I think he wants this:

 Dim tb as textbox = directcast(sender,textbox)

select case tb

case allthecases

 end select

Or, I would do this:

Dim s as string = directcast(sender,textbox).tag

select case s

case allthecases

 end select

 and set the tags on the text boxes to something meaningful.

 

 

Answer 3

You misunderstood. The sender will be an object. Like:

if sender.Equals(tbOne) then status.Text = "Nothing too interesting."

But the sender is not always going to be a textbox. It can also be a TrackBar, a Checkbox, or a ComboBox.

The sub gets called on mousemove. If that helps at all.

Answer 4

What I said will work - set the tag properties on all of the controls in question, and cast to Control instead of Textbox. 

 

Answer 5

Ok thank you cgraus. You posted when I was still typing. I was wondering if tag was going to ever be useful.

Answer 6

Yeah, I have to admit, some of my early C# code suffered from my not having worked out that 'tag' was there, and what it was good for :-)

 

Answer 7

 

My favorite trick in life is to store very complex datastructures in the tag.

I guess my own feeling is that an eventhandler that had multiple controls going through it is not well designed.

Every instinct reels against an event handler with a poutpouri of control types.

Answer 8

Yes, I admit that bit caught me by surprise as I expected it to be all the same control type at least.  However, I can see it.  He's setting the status text based on what control is being selected or used, from what I can tell.

 

Answer 9

That is exactly what I am doing. I am setting the status to display a certain string depending on which control currently has mouse focus.

Answer 10

You can use Select Case as in the following:

Select Case True
   Case sender Is TextBox1
      Label1.Text = TextBox1.Text
   Case sender Is TextBox2
      Label1.Text = TextBox2.Text
End Select

However, this translates into IL (and decompiled using Reflector) as:

 Dim flag1 As Boolean = True
      If (flag1 = (sender Is Me.TextBox1)) Then
            Me.Label1.Text = Me.TextBox1.Text
      Else
            If (flag1 = (sender Is Me.TextBox2)) Then
                  Me.Label1.Text = Me.TextBox2.Text
            End If
      End If

I don't know if this helps.

Answer 11

Public Class Form1

     Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)

           Handles Button1.Click

           whereFrom(sender.Name)

     End Sub

     Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)

          Handles Button2.Click

          whereFrom(sender.Name)

     End Sub

     Private Sub whereFrom(ByVal senderName)

          Select Case senderName

               Case "Button1"

                    Button1.Text = "sender"

                    Button2.Text = ""

               Case "Button2"

                    Button2.Text = "sender"

                    Button1.Text = ""

          End Select

     End Sub

End Class

... or you can just pass/examine sender.Name, instead of just sender.

 

Answer 12

Whenever I do so I always use Sender.Name. As long as it is a Windows Control Object it has a name value which you can then do a select case on.

Answer 13

As an alternative to the answers above, this also works well

 

        Select Case sender.ToString

            Case ControlItem1.Tag

            Case ControlItem2.Tag

        End Select

 

Set the tags accordingly