In this case, Form1 is the Main Form.
Pre-requisites: 2 Forms (Form1 and Form2), 1 Button (on Form1).
Public Class Form1
Function centerForm(ByVal Form_to_Center As Form, ByVal Form_Location As Point) As Point
Dim pLocation As New Point
pLocation.X = (Me.Left + (Me.Width - Form_to_Center.Width) / 2) '// set the X coordinates.
pLocation.Y = (Me.Top + (Me.Height - Form_to_Center.Height) / 2) '// set the Y coordinates.
Return pLocation '// return the Location to the Form it was called from.
End Function
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Form2.ShowDialog()
End Sub
End Class
Public Class Form2
Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Me.Location = Form1.centerForm(Me, Me.Location) '// center Form of Main Form.
End Sub
End Class
To center any other Form to the Main Form,
add the following code to the selected Form's .Load Event, as shown in the above code block for Form2.
Me.Location = Form1.centerForm(Me, Me.Location) '// center Form of Main Form.