How to call Sub/Function in New Form1 from Orginal Form1?

Question

Update:
Frm1A as new Form from Form1 .

I want to use only MainCal_Click in Form1 to order all new Forms to use Sub Cal of each Form.

Class Form1

  Dim Data as integer

  Sub Cal(byval x as integer)
     Data = Data + x
  End Sub

  Private Sub LoadOthForm_Click() 'Every time to create new Form when Click 
    Dim Frm1A as New Form1
    Frm1A.text = "Form1"..."Form2"... 'May 100+ Form  
    Frm1A.Show       
  End Sub

  Private Sub MainCal_Click() 'When click, it will order all new open form run Sub Cal()
    Data = 100
    For each frm as Form in Application.OpenForm
      if frm.Text = "From1" then
          frm.Cal(5) .......**** 'What code that new From can use Sub Cal ()? ****
      End if
      if frm.Text = "From2" then
          frm.Cal(15)
      End if
    Next
  End Sub

End Class

Answer 1

I happen to be on Form3 but it works the same as Form1. You need to have a reference to the new forms you create in order to call methods on them. I made the form variables at the class level so you could use them in both the LoadOthForm_Click and the MainCal_Click methods. You neve gave your new form instances a Name property so you cannot find them that way. You need to set the Data property for each form because each form has its own Data property. It is a class level field not a global. It added a label to show the result of the Cal method to demonstrate that the forms are running the method.

Public Class Form3
    Dim Data As Integer
    Dim Frm1A As Form3
    Dim Frm1B As Form3
    Dim Frm1C As Form3
    Sub Cal(ByVal x As Integer)
        Data = Data + x
        Label1.Text = Data.ToString
    End Sub

    Private Sub MainCal_Click(sender As Object, e As EventArgs) Handles MainCal.Click
        Frm1A.Data = 100
        Frm1B.Data = 100
        Frm1A.Cal(5)
        Frm1B.Cal(15)
    End Sub

    Private Sub LoadOthForm_Click(sender As Object, e As EventArgs) Handles LoadOthForm.Click
        Frm1A = New Form3()
        Frm1B = New Form3()
        Frm1C = New Form3()
        Frm1A.Show()
        Frm1B.Show()
        Frm1C.Show()
    End Sub
End Class

Answer 2

How is this?

Class Form1

    Private Data As Integer

    Sub Cal(ByVal x As Integer)
        Data = Data + x
        MsgBox(String.Format("{0}:{1}", Me.Text, Data.ToString))
    End Sub

    Private Sub LoadOthForm_Click(sender As Object, e As EventArgs) Handles LoadOthForm.Click
        For i = 1 To 10
            Dim f As New Form1
            f.Text = "FormA" + i.ToString
            f.Show()
        Next
    End Sub

    Private Sub MainCal_Click(sender As Object, e As EventArgs) Handles MainCal.Click
        Data = 100
        For Each frm As Form In Application.OpenForms
            If frm.Text = "FormA1" Then
                CType(frm, Form1).Cal(5)
            End If
            If frm.Text = "FormA2" Then
                CType(frm, Form1).Cal(15)
            End If
        Next
    End Sub

End Class