Old VB6 Dog, New .Net Tricks

I am a old VB6 programmer trying to learn VB.Net.

Under VB6, when referencing a control on another form, the only code needed to reference TextBox1 control on Form1 from the Click Eevent of Form2, would be following;


Form1.TextBox1.Text = "Test"

Now for my problem.

I tried a sample VB.Net application that has two forms, Form1 and Form2, each with a TextBox1 control. Form1 is designated as the project Startup Form. In Form1's Public Class module, I placed the declaration;

Public Form2 as New Form2

In Form1's Click event I placed the following code to Show Form2 and place the message "Test" in TextBox1.

Private Sub Form1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Click

Form2.TextBox1.Text = "Test"
Form2.Show()

End Sub

In Form2's Click Event I placed the following Code in an attempt to change the text in TextBox1 on Form1.

Private Sub Form2_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Click

Dim frm As Form1
frm.TextBox1.Text = "It worked"

End Sub

When I run this code I get the following error;

An unhandled exception of type 'System.NullReferenceException' occurred in WindowsApplication1.exe

Additional information: Object reference not set to an instance of an object.

My question is this, how do I get an Object Reference to Form1?

Any help would be appreciated.

Thanks,

Jim

The error means you haven't instantiated an object. Try declaring frm using the New keyword.

If you Dim it as New, it isn't the same object, so the textbox will never get set. That does get rid of the error though. :)

Here's an article explaining WHY this VB6 concept no longer works in .Net.

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dv_vstechart/html/vbtchWorkingWithMultipleFormsInVisualBasicNETUpgradingToNET.asp

As far as a solution, the most common way of handling this is to simply pass the first form to the constructor in the second form

'showing form2 from form1
Private Sub Form1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Click
Dim frm As New Form2(Me) 'pass this form
frm.TextBox1.Text = "Test"
frm.Show()
End Sub
'constructor code for form2
Private _frm As Form1

Public Sub New(ByVal frm As Form1)
MyBase.New()

'This call is required by the Windows Form Designer.
InitializeComponent()

'Add any initialization after the InitializeComponent() call

_frm = frm

End Sub
'set the textbox on form1 from form2
Private Sub Form2_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Click

_frm.Textbox1.Text = "It worked"

End Sub