Variable Inside Variable

  • Thread starter Thread starter Grant
  • Start date Start date
G

Grant

How do I, if at all possible, reference a variable with another variable
in VB.NET?

For example, if I have a form with a textbox and a button. Type var1 in
the textbox

Private Sub Button_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button.Click

dim var1 as string
var1 = "Hello World"
msgbox( /// display the contents of var1 using what was entered in
the textbox /// )

End Sub

Is this possible?

Thanks!
 
How do I, if at all possible, reference a variable with another variable
in VB.NET?

For example, if I have a form with a textbox and a button. Type var1 in
the textbox

Private Sub Button_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button.Click

dim var1 as string
var1 = "Hello World"
msgbox( /// display the contents of var1 using what was entered in
the textbox /// )

End Sub

Is this possible?
Click to expand...


You can kind of do it with System.Reflection. However, the variables
you are getting the values of must be public fields of a class. In the
following example, the form has a single text box named TextBox1, and
a button named Button1. The var1, var2, and var3 variables are public
fields of Form1. Reflection is used to get info about the field given
the name typed into TextBox1, and then to get the value of that field
in Me (the current instance of Form1). You should be able to type
"var1" in the text box and press the button to see it's value appear
in the form caption.

There are better ways to check for errors, this is kind of a hack for
less typing, but you might want to just check for a null return from
GetField() instead.

There is no straightforward way to use System.Reflection to get the
value of a local variable, or of a private field.

===

Public Class Form1

' Variables must be public fields of class. They can't be private,
' and they can't be local variables of a method.
Public var1 As Integer
Public var2 As Integer
Public var3 As Integer


Private Sub Button1_Click(ByVal sender As System.Object, ByVal e
As System.EventArgs) Handles Button1.Click

var1 = 111
var2 = 222
var3 = 333

Dim varname As String = TextBox1.Text ' name of variable to
get value of

Try
Dim obj As Object =
GetType(Form1).GetField(varname).GetValue(Me)
Dim val As Integer = CInt(obj) ' val is value of variable
now
Me.Text = val
Catch
' GetType(form1).GetField(varname) is null if varname
unknown, so
' calling GetValue() on that will raise
NullReferenceException.
Me.Text = "Invalid variable name"
End Try

End Sub

End Class

===

HTH,
Jason
 
Grant,

You will get a lot of answers, this is the most basic of Net programs
languages.

msgbox(var1 & textbox1.Text)
'assuming that the name of your textbox is textbox1

Others will show probably as well
MessageBox.Show(textbox1.Text & var1)
I use the latter, however that is just a matter of preference.

Cor
 
Grant said:
How do I, if at all possible, reference a variable with another
variable in VB.NET?

For example, if I have a form with a textbox and a button. Type
var1 in the textbox

Private Sub Button_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button.Click

dim var1 as string
var1 = "Hello World"
msgbox( /// display the contents of var1 using what was entered in
the textbox /// )

End Sub

Is this possible?
Click to expand...

Do you know why variable names have been invented? Do you know what
compiling means?


Armin
 
Hello Grant,

I wonder, for what would you need that?
If it's about your example, then it is unnecessary as you could
reference the text box directly.

TextBox1 contains the text "Hello World"

Private Sub Button_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button.Click

MsgBox(TextBox1.Text)

End Sub


Normally, I would not expect a user to know what variables are used in a
program. So, the input of a variable name which a user entered can match
the variable name in a program only by a very slight chance.

However, if there is only a limited number of variables used in your
program, you could list them in a ComboBox/ListBox and return the
content of that variable depending on the variable the user selected.
But consider, that variable names (e.g. var1, var2, var3) don't really
give much info about what the variable contains. Therefore, it might be
better to add the contents of the variables to the ComboBox/ListBox and
let the user choose from those.

Best regards,

Martin
 
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