Pass controls from Form1 to form2 - option 1 works, option 2 does not?

Pass controls from Form1 to form2 - option 1 works, option 2 does not?

• Todd Kitta

  Hi,

  First, please take a look at this article: http://msdn2.microsoft.com/en-us/library/87y2hdsf.aspx.

  With the Application Framework in Visual Basic 2005, the My.Forms object provides an instance of each form in your project. So for your case, you have My.Forms.MainForm, My.Forms.Form1 and My.Forms.Form2 as instances that you can access throughout your application. You can also access them by MainForm, Form1, Form2 (that's actually what you are doing here).

  In your case:
  - In Form2 code, by using Form1, you're accessing the default instance of Form1.
  - Option 1: You create a different instance of Form1 (myForm1) and load this instance. Form1 default instance is not loaded, so its ComboBox is still empty. Form2 ComboBox will be empty because it uses Form1 default instance.
  - Option 2: You replace "myForm1" with "Form1". Now you're loading Form1 default instance and populating its ComboBox. That's why Form2 ComboBox can get the values.

  So you can:
  - Use the default instances through your application (the easy option), for example you only need this in MainForm's OpenForm1Button_Click:
      Dim result As DialogResult = Form1.ShowDialog
  and this in Form1's OpenForm2Button_Click
      Dim result As DialogResult = Form2.ShowDialog()

  - Create other instances of the forms. In this case, you have to pass myForm1 instance to Form2 by setting a propery or through a constructor.

  Best regards,

  
  
  

• Christopher Smith

  Hello Ed,

  In option 1, I do read the content of comboBox from Form1 successfully.

  In my program, I actually go further and pass across the content of the ComboBox Drop-down list as well.

  But that only happens when Form1 was initially opened as shown in option1.

   

  If I open Form1 as an instance as shown in option 2, then nothing is reachable from Form2.

  My problem is, eveywhere I read up on the subject seems to indicate that I should be opening the Instance of forms. And that does not work.

  I think I am missing something in my code or obviously I do not understand something.

   

  By the way, all my forms have this line: 

  Inherits System.Windows.Forms.Form

  at the front.

   

  Bernard

   

  
  

• rohit_singh1679

  Thanks for your help.

  This clears up something I did not understand regarding the existance of the default instance of the form.

  I will stick to the default instances and this will assure the desired result in my case.

   

  I find that sometimes I spend enormous time trying to solve problems

  and in this case I had put my project on hold a week ago to research this question.

  Thanks to both  Ed Tenholder and Huy Nguyen for your help and putting me back to work.

   

  Bernard

   

  
  

• leriksen71

  hi Ed,

  Thanks for your persistence, and thanks a lot for trying to help me.

  Here is a simplified version of the code:

  MainForm: with a button to open Form1 (this is where the form1 can either be opened as an instance or as the form itself)-Version1 or 2.

  Public Class mainForm

  Inherits System.Windows.Forms.Form

  Private Sub mainForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

  End Sub

  Private Sub OpenForm1Button_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OpenForm1Button.Click

  Dim myForm1 As Form1

  Dim result As DialogResult

  myForm1 = New Form1() 'create instance of form

  result = myForm1.ShowDialog

  'Close form and set instance of form to nothing

  myForm1 = Nothing

  End Sub

  End Class

   

  FORM1: with a ComboBox named ComboBox and a Button to open Form2

  Public Class Form1

  Inherits System.Windows.Forms.Form

  Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

  ComboBox.Text = "20"   'Just a dummy value for testing and filling ComboBox display

  ComboBox.Items.Clear() 'zero drop down list

  Dim ic As Integer = 0

  Do While ic < 11 '# of items in list

  ComboBox.Items.Add(ic.ToString()) 'Place something in DROP-DOWN LIST (JUST FOR TESTING)

  ic = ic + 1

  Loop

  End Sub

  Private Sub ComboBox_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox.SelectedIndexChanged

  End Sub

  Private Sub OpenForm2Button_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OpenForm2Button.Click

  Dim myForm2 As Form2

  myForm2 = New Form2()

  Dim result As DialogResult

  result = myForm2.ShowDialog

  myForm2 = Nothing

   

  End Sub

  End Class

   

  FORM2: with a ComboBox named ComboBoxForm2 which should receive the data from Form1.ComboBox.

  Public Class Form2

  Inherits System.Windows.Forms.Form

  Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

  MessageBox.Show(" ComboBox from Form1= " & Form1.ComboBox.Text)

  'Fill Form2 ComboBox drop-down list with Form1 data

  ComboBoxForm2.Items.Clear()

  Dim ic As Integer = 0

  If Not Form1.ComboBox.Items Is Nothing Then ' If there is a drop-down list in Form1 ComboBox

  Do While ic < Form1.ComboBox.Items.Count '# of items in drop-down list

  ComboBoxForm2.Items.Add(Form1.ComboBox.Items.Item(ic)) 'Bring it across, starts with index of 0

  ic = ic + 1

  Loop

  End If

  'fill Form2 comboBox window with Form1 data.

  ComboBoxForm2.Text = Trim(Form1.ComboBox.Text)

  End Sub

  Private Sub ComboBoxForm2_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBoxForm2.SelectedIndexChanged

  End Sub

  End Class

   

   

  HERE it is. By changing "myForm1" to "Form1" in the "Form1 call" in MainForm in the 2 lines:

   result = myForm1.ShowDialog

  'Close form and set instance of form to nothing

  myForm1 = Nothing

  IT WILL WORK ON MY MACHINE.  I know I must be missing something.

  
  

• Dale

  What happens when you run Option 2

  Is MyForm1 in scope

  Could you post the entire code

   

     Ed Tenholder

  
  

• robosport

  Are you actually able to successfully execute the Option 1 code

    Ed Tenholder

  
  
• Pass controls from Form1 to form2 - option 1 works, option 2 does not?