Access Object in Form Class

Question

A follow-up question to one earlier: I've created an object in the Form1 : Form class with:

public struct POStruct
    {
        public List<string> staticCustInfo;
        public List<List<string>> itemCollection;
        public int testInt;
    }

    POStruct myObject = new POStruct();

However, when I try to access myObject from public void ItemSubmit_Click_1(object sender, EventArgs e) I get errors saying it's not instantiated. I thought I already instantiated it above with the line POStruct myObject = new POStruct();?

Thanks for the help.

You almost never need a `struct` in .NET; they have some surprising behaviour. This should probably be a `class`. — Tim Robinson, Nov 11 '10 at 19:20
@Tim: I don't think the behavior of value types is the issue here. — cdhowie, Nov 11 '10 at 19:22
No, but I'm predicting some `struct`-related surprises soon. http://stackoverflow.com/questions/13049/whats-the-difference-between-struct-and-class-in-net — Tim Robinson, Nov 11 '10 at 19:24

score 1 · Answer 1 · answered Nov 11 '10 at 19:16

It's likely that you are using one of the members of the struct without first initializing it. Structs cannot actually be null anyway, but their members can.

In other words, myObject is not null, and cannot actually be null since it is a variable of a struct type. But from your question, it sounds like myObject.staticCustInfo and myObject.itemCollection are.

But without seeing the exact code that is triggering the exception, all I can do is guess.

score 0 · Accepted Answer · answered Nov 11 '10 at 19:47

You're instantiating POStruct, but that struct has two List<> objects that aren't instantiated. When you instantiate myObject, you need to set these two properties to something of use, e.g.:

POStruct myObject = new POStruct();
myObject.StaticCustInfo = new List<string>();
myObject.itemCollection = new List<List<string>>();

If that doesn't help, can you post the whole class, with event handler, the exact message, and the line of code that's triggering the exception?

Access Object in Form Class

2 Answers2