Delegates and Events

Oh…spent lot of time trying to pass values between Parent and Child forms. It is much needed for my SoftPhone application to keep track of call states across windows. Finally, I was able to achieve it using delegates and events (interesting concepts, though)

To pass value from Parent (Form1) to Child Form (Form2)

Step 1: Create delegate for function

Public Delegate Sub PassData(ByVal Message As String)

Step 2: Create Object for deleage

Public frm2PassData As PassData

Step 3: Create public procedure in child form with same signature as delegate

Public Sub GetData(ByVal Message As String)
    TextBox1.Text = Message
End Sub

Step 4: Link Delegate with frm2 function

frm = New Form2
frm2PassData = New PassData(AddressOf frm.GetData)

frm.show

Step 5: To pass data from Parent Form to child form, just call delegate object as below

if frm2passdata isnot nothing then

frm2passdata(“Hello”)

end if

To pass value from Child Form to Parent Form (use Events)

Step 1: Declare Public event in Child Form

Public Event Notification(ByVal Message As String)

Step 2: RaiseEvent in Child form, as applicable

Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged
     RaiseEvent Notification(TextBox1.Text)
End Sub

Step 3: Create procedure in Parent form with same signature as Event

Public Sub Getdata(ByVal Message As String)
     Me.Text = Message
End Sub

Step 4: Add event handler for child form

AddHandler frm.Notification, AddressOf Getdata

Done..easy isn’t it?