Passing values between forms

[smeyer52]

Please help me pass a value from form2 back to form1. I am obviously a novice.

Form1 has textbox displaying the client's order, and a button to place order. Form1.button_click pops up form2.

Form2 displays listbox with multiple choices.
Form2 also has button to accept order, which will then be displayed in form1.textbox.

Form2.button_click code:
Private Sub btnAccept_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAccept.Click
Dim strOrders As String = ""
Dim strOrder As String = ""
Dim frm1 As Form1

'create a string from the selected lines in list box
For Each strOrder In ListBox1.SelectedItems
strOrders &= strOrder
Next

'now pass the string back to form1's text box
frm1.TextBox1.Text = strOrders
'compiles but will not run
'error: Object reference (frm1) not set to an instance of an object.
End Sub

Obviously I do not know how to refer back to form1 and its textbox from form2. Thanks for any help.

 

[PankajBanga]

change

Dim frm1 As Form1

to

Dim frm1 As New Form1

 

[PankajBanga]

When we create a variable, it doesn't have an object instance associated with it, you are simply identifying the type of object.

To create an instance of the object New keyword is used

 

[RiverGuy]

Take the above advice.

But to do what you want to do, there are many, many ways. You really don't want to access Form1 from Form2. You can make a static variable in your Form2, or you can do something like this:

Form2:

Public Class Form2
    Inherits System.Windows.Forms.Form
    Dim txt As System.Windows.Forms.TextBox

     Public Sub SetText(ByRef text As   System.Windows.Forms.TextBox)
        txt = text
     End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        txt.Text = "This text is being set in Form2."
    End Sub
End Class

Form1:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim f2 As New Form2()
        f2.SetText(TextBox1)
        f2.Show()
End Sub

 

[smeyer52]

Thanks, PankajBanga; but the code "Dim as New" creates a new instance of form1 when I already have the original form1 on the screen. So I wind up with two Form1 objects on my screen.

I intend for form1 to up form2, but to remain visible while passing focus to form2. Form 2 will ideally update form1 and then close, passing focus back to form1.

 

[RiverGuy]

I think he is just giving you an example. Apply his idea to your Form2, not Form1.

 

[PankajBanga]

use the following code on Button Click event of Form1

Dim frm As New Form2()
frm.ShowDialog(Me)
Me.TextBox4.Text = frm.ListBox1.SelectedItem

TextBox4 is the textbox on Form1 where you want to display the Item selected from ListBox

NOTE: a form will not be displayed untill u use Show or ShowDialog method even though you have Instantiated it.

 

[PankajBanga]

set the DialogResult property for the Accept button on Form2 to OK.

make sure you select an Item from the ListBox before you press accept

 

[smeyer52]

Thanks, PankajBanga. That solution worked.

Instead of form2 passing the value to form1, which form2 could not see as instantiated, form1 retrieves the value from form2, which form1 instantiated. Also, I was using frm.show(), but it only works correctly with frm.showdialog().

THanks again. I hope to learn a lot more VB.net.