Is the .Tag property a reference or an instance of an object?

[joelwenzel]

Some controls have a Tag property that you can set to equal an object. Does this create a copy of the object of just a reference to the original?

 

[TipGiver]

The .Tag property is for saving extra information to a control. You can use it the way you would use a public variable, or as you want/need. It is an optional property and can be used for get/set at run-time.

 

[mansii]

Agree.
Tag is a member of an object's properties. Setting it's value will not create a copy of the object.

 

[Borvik]

I think what joelwenzel is asking is - Does changing the value you set in Tag reflect on the original variable you used to set the Tag?

The answer is the value stored in Tag is just a copy - for a quick example:

Dim x As Integer = 5
Button1.Tag = x
Button1.Tag = 2
MsgBox(x)

While the tag does change - x does not and the MsgBox shows 5.

 

[joelwenzel]

ok, I've been experimenting with the tags and I think they store references to the original object, not a copy...because if I change a setting use the object stored in the tag, the original changes as well.

Thanks everyone for your input.

 

[TipGiver]

I would say a copy of an object. Try Borvik's code to see that the message box shows 5. Then try mine to see that it shows 5 again:


Dim x As Integer = 5
TextBox1.Tag = x
x = 2
MessageBox.Show(TextBox1.Tag)

 

[stsuing]

'Integer is a value type therefore it is a copy. If you used a reference you would see a 2

Public Class foo
Public num As Integer
End Class

Dim f As foo = New foo
f.num = 5
TextBox1.Tag = f
f.num = 2
MsgBox(f.num)

 

[Borvik]

Thanks for pointing that out stsuing!

Although just to point out - your MsgBox is displaying the exact one you changed according to that code so of course that will work. You would want to display the TextBox1.Tag.num according to your code - which does indeed change by reference.

 

[joelwenzel]

yes integer is a copy. I'm using objects though