Thread: Calling void isn't creating instance of an object

I can't seem to work out why an instance of an object isn't getting created when I create it in a sub routine.

In Page_Load if i have this:-

Code:

private Order order;
protected void Page_Load()
{
   if(!ispostback)
   {
      buildOrderItemList(ActionChoice.Build);
      order = new Order();
      order.orderItems = new List<Product>();
      order.id=-1;
      this.dlstOrderItems.DataSource=Order.orderItems;
      this.dlstOrderItems.DataBind();
   }
}

protected void buildOrderItemList(Action)
{
   Order order = new Order();
   order.orderItems = new List<Product>();
.
.
.
}

Without the lines in red, I get "instance of an object" error. If I create the instance in the page load I don't get the error.

I use a similar technique with another Data List and it works fine.

Can't work out why the instance isn't working in the void.

Any ideas?

You have a class called "Order". This is a reference type. When you declare a variable of a reference type at run time, the variable contains the value null until you explicitly create an instance of the object by using the new operator, or assign it an object that has been created elsewhere by using new.

On this page, you simply have:

Code:

private Order order;

What you want is:

Code:

private Order order = new Order();

OR, if you have a method, like GetOrder, for example, which returns an instance of the class, then you could have something like this:

Code:

private Order order = Orders.GetOrder(orderID);

Make sense?

That's what I have. The variable is used throughout the page hence the page wide declaration.

If I create the instance directly in the Page_Load event, it works fine. If I try and create the instance inside a routine called from Page_Load, it doesn't seem to work and I get the "instance of an object" error.

I can't seem to work out why that doesn't work.

Ah, just noticed an error in the code I posted. The 2nd portion should have been:-

Code:

protected void buildOrderItemList(Action)
{
   order = new Order();
   order.orderItems = new List<Product>();
.
.
.
}

Actually, just realised that is the error in my code...

It should have been like it is above. I had it as in my original post.

Originally Posted by richyrich

That's what I have.

No, you don't. You have declared it as:

Code:

private Order order;

This is NOT a new instance and will be null. Therefore, every method (i.e. page_load) that you use this in, you'll need to create an instance:

Code:

order = New Order();

Sorry, I didn't mean that's what I have. I knew what I meant...

I meant I knew what you were talking about. I just declared another instance of it instead of referring to the page wide declared variable.