Access form objects from other forms.

Question

Greetings.

Is there a relatively easy way to access objects on a different form within the same project in VB2015 ?  In an earlier version of VB, I could, for example, reference form1.label1.text or form1.textbox.text from form2 or other forms.  I could also reference public variables in other forms to get already computed data, etc.  I am having difficulty finding this in VB2015.

Answer 1

Hi

Yes, you can do that. Here is code for 2 Forms to illustrate

FORM1

' Form1 with TextBox1 (text="Freddy wuz heer")
Option Strict On
Option Explicit On
Option Infer Off
Public Class Form1
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Form2.Show()
    End Sub
End Class

FORM2

' Form2 with TextBox1 (blank)
Option Strict On
Option Explicit On
Option Infer Off
Public Class Form2
    Private Sub Form2_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        TextBox1.Text = Form1.TextBox1.Text
    End Sub
End Class

---

Regards Les, Livingston, Scotland

Answer 2

BB,

Consider creating a NEW instance of the other form - rather than using the default instance.

In the other form's code, for anything that you need access to, create public read-only properties and the rest is then obvious from there.

---

"A problem well stated is a problem half solved.” - Charles F. Kettering

Answer 3

The following can be downloaded from here.

Public Class Form1
    Private _Value As String
    Public ReadOnly Property Value As String
        Get
            Return _Value
        End Get
    End Property
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        _Value = "Karen"
        Dim f As New Form2
        f.Owner = Me
        Try
            f.Label1.Text = "Hello from parent"
            f.ShowDialog()
        Finally
            f.Dispose()
        End Try
    End Sub
End Class

Child

Public Class Form2
    Private ownerForm As Form1
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        If Not String.IsNullOrWhiteSpace(TextBox1.Text) Then
            ownerForm.TextBox1.Text = TextBox1.Text
        Else
            ownerForm.TextBox1.Text = "Hello from child"
        End If
    End Sub
    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        MessageBox.Show(ownerForm.Value)
    End Sub
    Private Sub Form2_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        ownerForm = CType(Owner, Form1)
        TextBox1.Text = ownerForm.TextBox1.Text
    End Sub
End Class

---

Please remember to mark the replies as answers if they help and unmark them if they provide no help, this will help others who are looking for solutions to the same or similar problem. Contact via my Twitter (Karen Payne) or Facebook (Karen Payne) via my MSDN profile but will not answer coding question on either.
VB Forums - moderator

Answer 4

Is there a relatively easy way to access objects on a different form within the same project in VB2015 ? 

It depends on what the connection between the forms is.  Data that is required to populate controls on the new form when it is first shown is best passed in the constructor.  Other data to be accessed by the new form can be accessed from properties in the original form if a reference to the original form is provided to the new form, or properties of controls can be made available by passing a reference to the control.  Data that needs to be updated when it changes in the original form can be passed by messaging.  All these options are described here:
https://vbdotnetblog.wordpress.com/forms/

Whichever techniques you use, do not use the default form instance - it will certainly create problems later on. 

Answer 5

I am having difficulty finding this in VB2015.

That's intentional. Those old VB6 habits made it difficult to apply good object oriented principles and were encouraging coding antipatterns.  If you compute some data in one place and need to use it in other places then that data should belong to its own object which can be passed around between the object which produces it and the object(s) which consume it.  If something happens on Form2 which should cause the value of the text on a Label on Form1 to change, then Form1 should likely be wired to listen for an event which Form2 raises and then respond to that event.  Even in the absence of strong application of the encapsulation principle, you should still be explicitly providing Form2 with an instance of Form1 in order to access the label, or passing Form2 a reference to the specific Label to manipulate.

Karen has shown a simple example of passing a Form reference, and while you can do this, it should only be done in the most simple of scenarios.  As soon as you need to manipulate the other form in multiple ways, or need to pass the instance to multiple other forms, you immediately begin to build a spaghetti code situation where a given object is being manipulated in so many places and for so many reasons that it becomes very difficult to track down a bug when one occurs.

If the text of, say, a status label needs to change frequently and by various means then there should likely be a single "StatusMonitor" class instance which becomes the sole source of changes to the label text.  Other Forms and objects can interact with the instance of StatusMonitor to alert the application to their actions and allow the StatusMonitor to worry about when and how to alert the user.  If you ever want to change the way alerts are displayed, you can do so in one place, regardless of how many other blocks of code may change the status.

Every application needs to draw a line between what can be done and what should be done to solve any given problem, and the placement of that line varies based on the size, scale, and intended usage of the application.

---

Reed Kimble - "When you do things right, people won't be sure you've done anything at all"

Answer 6

Hi BB2017，

Please remember to close your thread by marking helpful post as answer, it is very beneficial to the other communities who face the same issue.

Thanks for your understanding.

Best regards,

Cherry Bu

---

MSDN Community Support
Please remember to click "Mark as Answer" the responses that resolved your issue, and to click "Unmark as Answer" if not. This can be beneficial to other community members reading this thread. If you have any compliments or complaints to MSDN Support, feel free to contact [e-mail].