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passing variables between forms

I am having serious issues trying to take data from one form and passing it to another form... I have a 3 form new employee application that gets information from the new employee in textboxes and then sends it to a database... my problem is that once i make an instance of the form: dim theFirstForm as new Form1... and dime theSecondForm as new Form2. i cant seem to figure out how to access it and store it in variables... so that on the third form i can access it and populate a database with all the information. My programming teacher made the suggestion to make a new class and send all the info to the class and then on the submit button access it from there and then populate the database... any suggestions on the best way to do this? i have been reading about passing variables and such but somehow i am just not getting it :(... PLEASE HELP ME!!!!!

[860 byte] By [IGiberson] at [2007-12-24]

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# 1

Try this, add a new module to your project. In the module right under the first line enter Public <and you var>

Like this:
Module Module1
Public UserName, UserPassword As String
End Module

Wellnow at 2007-8-31 >

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# 2

there are quite a few threads about the same thing. In the previous post I had explained and gave you some code about passing variables to another form/class - thats exactly how its done :-)

Form1:

Dim theSecondForm as new Form2("Bob", "123 some street")

theSecondForm.ShowDialog()

Form2:

Dim theName as String

Dim theAddress as String

Public Sub New (byval name as String, byval address as String)

Me.theName = name

Me.theAddress = address

end sub

that's all there is to it to pass variables from 1 form to another. You increase the parameters to the amount you want to pass into the other class, and increase its constructor (new in this case)

ahmedilyas at 2007-8-31 >

# 3

Your question is a bit confusing...

Which form is the initial form (the one displayed first)? Is it Form3? The fact that you are using "Dim theFirstForm As New Form1" would inidicate that Form1 is not the startup form... If you use "Dim theFirstForm As New Form1", then you can access all the TextBoxes on Form1 directly using your variable: theFirstForm.FirstNameTextBox.Text

ahmedilyas gave you an answer... if you're not getting it that would indicate that you're trying to do something that you're not explaining... If the answer you got doesn't help, try to give us a clearer indiciation of how your program is supposed to operate: as in, which form loads first, when/how are the other forms displayed, where are you delcaring the instances of Form1 and Form2, etc.

rkimble at 2007-8-31 >

# 4

Here is how I do this (There are many ways). It works well to a point.

We're going to deal with static data so the allocated storage will

exist during the entire run-time.

Add a new class to yopur project. Name it what ever you want. Make it look something like this:

Imports Microsoft.VisualBasic

Public Class Common

Public Shared sDateTime As String

Public Shared sReportName As String

Private Sub New()

'Makes this class uninheritable

End Sub

End Class

...........................

Now, when somebody (in this case) fills in the textboxes from one of your forms classes you'd do something like this:

Common.sDateTime = Textbox1.Text

Common.sReportName = Textbox2.Text.
Now when you need to get the information from yet another forms class

you access the fields again. If your writing them out to a database you

can put them in your sql string as is:

Dim sSql as string = "Insert Into tblWhatever(Date, ReportName) Values('" + Common.sDateTime...

You get the picture. I don't want to give to much away...

ocertain at 2007-8-31 >

# 5

This is entirely an issue of personal preference, but I would strongly reccomend against using a global variable to pass data between forms. This includes using static class members and fieds inside of modules.

The reason I reccomend against this is simple: as your application logic grows more complex, debugging the use of global variables can become extremly difficult. In particular, because a global variable may be set anywhere in code, you may find yourself in the future pulling your hair out trying to figure where exactly a particular value is getting set.

If, however, you pass data between your forms by setting instance variables on the form, it is much easier to track the flow of information through your application.

You can do this either by adding parameters to the constructor of your form, as was suggested above, or by creating a property on your form that you use to set the necessary state from your secondary form.

ScottWisniewski-MSFT at 2007-8-31 >

# 6

ahmedilyas wrote:

there are quite a few threads about the same thing. In the previous post I had explained and gave you some code about passing variables to another form/class - thats exactly how its done :-)
Form1:
Dim theSecondForm as new Form2("Bob", "123 some street")
theSecondForm.ShowDialog()
Form2:
Dim theName as String
Dim theAddress as String
Public Sub New (byval name as String, byval address as String)
Me.theName = name
Me.theAddress = address
end sub
that's all there is to it to pass variables from 1 form to another. You increase the parameters to the amount you want to pass into the other class, and increase its constructor (new in this case)

I tried passing parameters from one form to another using the above suggested method.

The problem I am running into is, on my form I have a Label field. I want to change the text property of this label field to contain

the text that is passed to the form as a prameter.

Here is the code that I am using.

Public Class Lookups
Inherits System.Windows.Forms.Form
Public Sub New(ByVal TableType As String)
Select Case TableType
Case "Vehicle Type"
Vehicle_Type(TableType)
End Select
End Sub
Private Sub Vehicle_Type(ByVal TableType As String)
lblSubHeading.Text = TableType
ListBox1.DataSource = VTypeDS2
ListBox1.DisplayMember = "Vehicle Type"
End Sub
End Class

The following error I am getting is at the red line of code above....

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

Any ideas as to why I receive this error ?

thanks

tattoo

tattoo at 2007-8-31 >

# 7

tried doing it the other way? Really you shouldnt call methods from the New constructor but this should not be the problem.

Check to see in the debugger what lblSubHeading value is - if its nothing then thats the problem, looks like the control has not been instantiated

ahmedilyas at 2007-8-31 >

# 8

I tried calling my method from the form load routine and the program didn't know anything about the variable TableType that I had passed in..

I also looked at the value of the lblsubheading.text in the debugger and it is set as Nothing.... Why when this label was added at design time.

I can see it is defiend in the Windows Form Designer Generated Code so I don't understand why the app thinks it isn't instantiated.

If, as you say I shouldn't be calling any methods from the New Constructor, where should they be called from ?

If I call them from somewhere else, how do I get those methods to recognize the variables that I pass in....

thanks

tattoo

tattoo at 2007-8-31 >

# 9

the should be called seperately else where.

now if lblSubHeading is nothing, then create the Vehicle_type method as public, so the calling form can access this and set the text before showing this form and remove the New constructor on the look ups form.

//calling form:

Dim theLookUps as new LookUps()

theLooksUps.Vehicle_Type("boo")

//other form:

public sub Vehicle_Type(byval TableType as string)

'rest of code here

end sub

ahmedilyas at 2007-8-31 >

# 10

Have you checked the value of the TableType variable when it is first set? That Select statment will only set the variable on a very specific value. Are you sure that "Vehicle Type" is the value you passed to the form? Nothing else will work, the way you've written it.

And I'm not sure what could be wrong with calling initialization subroutines from the constructor... forms do it implicitly with the call to InitializeComponent() and structured code design almost dictates that additional initialization code should be wrapped into common routines and called in the same manner.

rkimble at 2007-8-31 >

# 11

Is there a way, when calling Form2 from Form1, that I can get Form2 to return a string back to Form1 ?

In Form1 I want to allow the user select from a list of email addresses. Form2 is the form that maintains this list.

thanks

tattoo

tattoo at 2007-8-31 >

# 12

there is. you could either:

set a public property which will store the value to return back to the caller (form1)

just call the method in form2 which will return back the email address you are after. example:

//form2:

public function DoGetAddress() as String

return "some email address"

end function

//form1:

Dim theForm2 as new Form2()

MessageBox.Show(theForm2.DoGetAddress())

does this help?

ahmedilyas at 2007-8-31 >

# 13

Once again, thank you very much, that worked great..

tattoo

tattoo at 2007-8-31 >

# 14

Oops !!!! I spoke to soon.....

I tried your suggestion above and it did work when I hard coded an email value to be returned but what

I actually want to do is display the second form to allow the user to select a valid email address from the database.

below is the code I used, the problem I have run into is that the line I used to display the form to select the email address leaves the form on the screen and doesn't allow me to select a value and return.

any ideas ?

'Calling Form
Private Sub btnemail_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnemail.Click
Dim MailAddress As String
Dim Address As New NetAddresses
MailAddress = Address.GetDat()
System.Diagnostics.Process.Start("mailto:" & MailAddress)
End Sub
'Called Form
Public Class NetAddresses
Inherits System.Windows.Forms.Form
Dim Message As String
Public Function GetDat()
SqlDataAdapter1.Fill(Addresslist, "NetAddress")
Me.Show()
Return CboAddress.Text
End Function

tattoo at 2007-8-31 >

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