How can I implement event handlers in a class?

Question

Hi all of you,

My project has around thirty winforms. I am thinking how can I avoid to write for every winform the following three subs (I think such code is very auto-descriptive):

Is it possible to define form event handlers in a class?

Public Sub Definir_focos()

        For Each c As Control In Me.Controls

            If c.GetType Is GetType(TextBox) Then

                AddHandler DirectCast(c, TextBox).GotFocus, AddressOf conFoco
                AddHandler DirectCast(c, TextBox).LostFocus, AddressOf sinFoco
            End If

            Select Case c.HasChildren
                Case True
                    For Each c2 As Control In c.Controls
                        If c2.GetType Is GetType(TextBox) Then
                            AddHandler DirectCast(c2, TextBox).GotFocus, AddressOf conFoco
                            AddHandler DirectCast(c2, TextBox).LostFocus, AddressOf sinFoco
                        End If
                    Next
            End Select

        Next
   
    End Sub

Private Sub conFoco(ByVal sender As Object, ByVal e As System.EventArgs)
        DirectCast(sender, TextBox).BackColor = Color.Yellow
End Sub

Private Sub sinFoco(ByVal sender As Object, ByVal e As System.EventArgs)
        DirectCast(sender, TextBox).BackColor = Color.White
End Sub

How could I encapsulate that logic in a class?

Thanks for your help,

---

enric

Answer 1

Hi,

extend the Form-class. Derive from Form, add your methods, use this custom Form as Forms in your project.

Or add these methods to your mainform, make them public or internal, pass a reference to "other"-forms/controls as parameter to the methods -or make the methods static...

Regards,

  Thorsten

Answer 2

Hi just a silly question.. or not

Following your advices everything is fine but.. could I avoid InitializeComponent method in that class?

---

enric

Answer 3

I mean, everytime I delete these lines, then the compiler creates them again:

That means that Form class implement an inteface which has two compulsory methods (initializecomponent and Load??

 Private Sub FormularioEventos_Load_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    End Sub
    Private Sub InitializeComponent()
        Me.SuspendLayout()
        '
        'FormularioEventos
        '
        Me.ClientSize = New System.Drawing.Size(292, 273)
        Me.Name = "FormularioEventos"
        Me.ResumeLayout(False)
    End Sub

TIA

---

enric

Answer 4

Hi Enric,
The InitializeComponent method has a comment preceding it, warning you not to modify the code. By modifying the code in the InitializeComponent method, you can no longer use the Forms Designer. If you do, your modifications will be lost. You should only perform these optimizations as the final stage of development, after all the design work has been done.
If you edit anything in the designer, the InitializeComponent method will be created again.
Best Regards,

---

Bob Wu [MSFT]
MSDN Community Support | Feedback to us

Answer 5

Rather than putting this at form level, you could subclass the standard controls themselves - TextBox, ComboBox etc. - and override this behaviour there:

Class TextBox2 
   Inherits TextBox 
   Public Sub New() 
      MyBase.New() 
   End Sub 

   Protected Overrides Sub OnLeave( _
        ByVal sender as Object _
      , ByVal e as EventArgs 
      )
      Me.BackColor = Color.White 
   End Sub 

   Protected Overrides Sub OnEnter( _
        ByVal sender as Object _
      , ByVal e as EventArgs 
      )
      Me.BackColor = Color.Yellow 
   End Sub 

End Class 

Then just use TextBox2 controls everywhere you would have used TextBox ones and the colouration is done automagically.

---

Regards, Phill W.

Answer 6

Thanks Pill

---

enric