VB.NET Object Problem with Collections, Arrays and Lists

Question

I have a small program where I have been trying to create collections of a particular object I have created (Job).

Regardless of whether I am using an array, collection or list, each time I add a new instance of the object to the array/collection/list, it overwrites all previous items with the same object.

For example, let's say Job has only one property, name. If I were to have Jobs with names 1,2,3,4 in a collection, each time I add the individual job, all previous jobs get the name of the current job. So by the time I add job 4, all the jobs have the name of 4.

Has anyone experienced this issue before?

I'm pretty sure you're doing something wrong, what about some piece of code? — dr. evil
– dr. evil, Commented Feb 17, 2009 at 23:39

Marc Gravell · Accepted Answer · 2009-02-17 23:39:33Z

2

I suspect you are adding the same instance multiple times - i.e. (I'll use C# here...)

Job job = new Job();
job.Name = "a";
list.Add(job);
job.Name = "b";
list.Add(job);

What you have done is add 2 references to the same object to the list. What you should have done was:

Job job = new Job();
job.Name = "a";
list.Add(job);
job = new Job(); /// <<===== here
job.Name = "b";
list.Add(job);

This is because classes are reference-types; all you are adding is a reference. Structs are value-types, and would work like you expect, except that unless you really know what you are doing, structs should be immutable (i.e. no editable properties once created).

answered Feb 17, 2009 at 23:39

Marc Gravell

1.1m273 gold badges2.6k silver badges3k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

S N Over a year ago

I thought something like that was happening! Thanks a lot for your answer, you saved me a lot of aggravation.

baretta · Accepted Answer · 2009-02-17 23:40:31Z

0

It would sound as if your were reusing the Job object variable after adding it to the list, without recreating the Job object. All items in the list will point to this object.

answered Feb 17, 2009 at 23:40

baretta

7,6451 gold badge29 silver badges25 bronze badges

Collectives™ on Stack Overflow

VB.NET Object Problem with Collections, Arrays and Lists

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related