How to check if a variable is holding any reference?

Question

Hello,

   How to check whether a variable is actually holding a reference or not?

   For example, suppose that I have declared [just declared not instantiated] 'b' as a button and later in the code I want to check if b is holding any reference a Button object. How to do this?

Thanks,
Raraju.

        

Answer 1

if (b != null)
{
   // it's holding a reference.
}

---

David Morton - http://blog.davemorton.net/ - @davidmmorton - ForumsBrowser, a WPF MSDN Forums Client

Answer 2

if (b != null)
{
   // it's holding a reference.
}

---

David Morton - http://blog.davemorton.net/ - @davidmmorton - ForumsBrowser, a WPF MSDN Forums Client

Thanks David. Bu can you let know how to do this in VB? Because I tried the following, but they didn't work!

IF b=Nothing -> it says that '=' operator is not defined for Button and Nothing
IF b.Equals(Nothing) -> if b doesn't have an object reference, this will throw an exception

Any other ideas?

-Raraju

Answer 3

if (b != null)
{
   // it's holding a reference.
}

---

David Morton - http://blog.davemorton.net/ - @davidmmorton - ForumsBrowser, a WPF MSDN Forums Client

Thanks David. Bu can you let know how to do this in VB? Because I tried the following, but they didn't work!

IF b=Nothing -> it says that '=' operator is not defined for Button and Nothing
IF b.Equals(Nothing) -> if b doesn't have an object reference, this will throw an exception

Any other ideas?

-Raraju

If b <> Nothing Then
   ' it's holding a reference.
End If

Also, I believe in VB, you can use "If b Is Nothing"

---

David Morton - http://blog.davemorton.net/ - @davidmmorton - ForumsBrowser, a WPF MSDN Forums ClientOr,

Answer 4

Hi,
You can also use

if (b IsNot Nothing) Then
'Holds a Reference
EndIf

Hope it helps

---

FEAR NOT TO BE JUST Please mark posts as answers/helpful if it answers your query

Answer 5

if (b != null)
{
   // it's holding a reference.
}

---

David Morton - http://blog.davemorton.net/ - @davidmmorton - ForumsBrowser, a WPF MSDN Forums Client

Thanks David. Bu can you let know how to do this in VB? Because I tried the following, but they didn't work!

IF b=Nothing -> it says that '=' operator is not defined for Button and Nothing
IF b.Equals(Nothing) -> if b doesn't have an object reference, this will throw an exception

Any other ideas?

-Raraju

If b <> Nothing Then
   ' it's holding a reference.
End If

Also, I believe in VB, you can use "If b Is Nothing"

---

David Morton - http://blog.davemorton.net/ - @davidmmorton - ForumsBrowser, a WPF MSDN Forums Client Or,

If b<> Nothing -> Operator '<>' is not defined for types 'System.Windows.Controls.Button' and 'System.Windows.Controls.Button'.

-Raraju

Answer 6

Hi,
You can also use

if (b IsNot Nothing) Then
'Holds a Reference
EndIf

Hope it helps

---

FEAR NOT TO BE JUST Please mark posts as answers/helpful if it answers your query

It worked!! Thanks Rahul.

-Raraju