Thread: Creating new instance of an object

Just wanted to check that when you use an object, is it given a value of null?

Eg if I have

Code:

Public Class myObj
{
   public int id {get; set;}

   public myObj()
   {
   }
}

And I use this in my page:-

Code:

myObj newObj;

is the value of newObj=null?
or do you have to create an instance?

Code:

myObj newObj = new myObj();

would newObj=null now?

Code:

myObj newObj;

this will be null.

Code:

myObj newObj = new myObj();

this will not be null.

OK. So if I had this:-

Code:

myObj = newObj;

Could I then do this?

Code:

if(ddl.selectedvalue=="-1")
{
   newObj = new myObj();
   newObj.id=-1;
}
else if(ddl.selectedvalue!="")
{
   newObj = myObj.GetObj(Convert.ToInt32(ddl.selectedvalue));
}
if(newObj!=null)
{
}else{
}

If I try that in VS, it gives me errors:-
myObj is a 'type' but is used like a 'variable'
newObj does not exist in the current context'

That was a typo, I corrected it above.

That's what I thought, but I was getting another error in VS.

Just realised the variable was created inside a different if...end if, so wasn't available in the context I was using if(obj!=null)

Doh...

It seems what you want is:

Code:

myObj newObj;
if(ddl.selectedvalue=="-1")
{
   newObj = new myObj();
   newObj.id=-1;
}
else if(ddl.selectedvalue!="")
{
   newObj = myObj.GetObj(Convert.ToInt32(ddl.selectedvalue));
}
if(newObj!=null)
{
}else{
}

Yeah, that's what I thought I was using, but I had it something like:-

Code:

if(thisistrue)
{
  myObj newObj;
  if(ddl.selectedvalue=="-1")
  {
    newObj = new myObj();
    newObj.id=-1;
  }
  else if(ddl.selectedvalue!="")
  {
    newObj = myObj.GetObj(Convert.ToInt32(ddl.selectedvalue));
  }
}
if(newObj!=null)
{
}else{
}

Actually, I double checked my code and I have as in your post.

But VS gives an error of "Use of unassigned local variable 'newObj'"

what line? and that's not an error, just a warning.

Here:-

Code:

myObj newObj;
if(ddl.selectedvalue=="-1")
{
   newObj = new myObj();
   newObj.id=-1;
}
else if(ddl.selectedvalue!="")
{
   newObj = myObj.GetObj(Convert.ToInt32(ddl.selectedvalue));
}
if(newObj!=null)
{
}else{
}

It comes up in the Error List of VS. I guessed it might not be a problem, but just want to check that my !=null condition will actually work correctly.