How to get a List item without reference

[tshad]

I am trying to get the 1st (or second) item from a list. I don't want the reference as I want to change a couple of fields before adding it back in and I don't want to change the original.

For example:

List<SomeClass> myClass = new List<SomeClass>();

myClass.Add(...);
myClass.Add(...);

SomeClass newClass;

newClass = myClass[0];    // this creates a pointer

newClass.name = "Joe";

I don't want myClass[0].name to be "Joe"

I don't want to clone the whole list, just one of the list items.

Thanks,

Tom

 

[xwb]

This is the C/C++ programmers nightmare when moving to C#. If you look up, C# deep copy there are lots of hits on how to do this.

The main thing is that the class must be marked as [Serializable]

 

[tshad]

Why would it have to be serializable if it is moving from one type to the same type?

Also, most of what I see is moving a list to another list. I haven't found one that shows how to move an item of the list to another item of the same type.

I also want to move it back into the list (which at this point can be a reference).

I just don't want to create a new type and have to copy each value from the list item to the new item when I can just copy it.

Thanks,

Tom

 

[tshad]

I found it.

I can implement the ICloneable interface on the class I am using, create a Shallow copy method that calls MemberwiseClone() and call that.

Since I am not concerned with reference values in the this class, it works fine.

Thanks

 

[xwb]

Basically depends on what sort of copy you want. As you said, ICloneable is for a shallow copy. For a deep copy you need it to be serializable.

The problem with the serializable/cloneable methods is you can make an instance without going through the constructor so it may miss some vital initializations. Just tread carefully when using them.

 

[Olaf Doschke]

The essential truth is, that myClass[0] is a reference, so when you change it you automatically also change the list item myClass[0] in the list. The list item itself only is a reference to the original object memory location, too.
The only way not to modify this object is to first make a copy. Whether you need a deep or shallow copy is a different matter, but you need a new instance. To have a separate pointer to the same memory doesn't make it a seperate object.

I learned that the other way around: Using an inital instance I set its fields to data coming from a database and aded each final item to a list, I ended up with a list of all items pointing to the same object, only its final state was saved many times (of course).

Bye, Olaf.