How to Create Generic Function

Level: Beginner

Knowledge Required:
Generics in Visual Basic

Introduction:
This article discusses how to create a Generic Function. Example: Create a Generic Function which is used to Find a Form in Open Forms. Useful for:

1) Preventing to create another instance of a Form
2) Finding a De-Activated / NOT Focused Window and set Focus on it

Description:
In my starting Post I discussed a situation where we require to find a Form which is opened. Now we will create a Generic Function which will return that particular type of Form.

Public Function GetWindow(Of T As Form)() As Form
    For Each frmEach As Form In My.Application.OpenForms
        If TypeOf frmEach Is T Then
            Return frmEach
        End If
    Next
    Return Nothing
End Function

Usage:

Public Sub ShowForm2()
    ' We will create a new instance of Form2
    Dim frmNew As Form2
    ' Call GetWindow() function which returns that type of Window if open
    frmNew = GetWindow(Of Form2)()
    ' GetWindow() returns NOTHING if window NOT found
    If frmNew IsNot Nothing Then
        frmNew.Show()
        frmNew.Focus()
    Else
        ' OK it means Window NOT Opened so create new instance
        frmNew = New Form2
        frmNew.Show()
    End If
End Sub