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c# 2010 winforms list of classes problem

Posted on 2013-12-16
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Last Modified: 2013-12-16
Hi

I have a class, like this:

class MyClass
{

public int ID {get; set;}
public string[] Stuff = new string[10];

public MyClass(int ID, string[] Stuff)
{

this.ID = ID;
this.Stuff = Stuff;


}

}

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simple enough...

I have a list of this class, which I am adding to like so

List<MyClass> myStuff = new List<MyClass>();

myStuff.add(new MyClass(id,stuff));

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this is fine when I add the first entry, but for subsequent entries, the 'stuff' array is being applied to ALL entries in the list, not just the new one.

I am baffled as to why, I am sure someone can enlighten me.


cheers

CD
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Comment
Question by:cycledude
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7 Comments
 
LVL 52

Expert Comment

by:Carl Tawn
ID: 39721140
You mean you are passing the same instance of "stuff" to each MyClass object? What you are actually passing is a pointer to the array, not a copy.

You should look at creating a copy of the array inside each MyClass instance if you want them to remain separate.
0
 

Author Comment

by:cycledude
ID: 39721148
well, its the same array structure as in

string[] stuff = new string[10]

but the contents of the string are different on each iteration
0
 
LVL 52

Expert Comment

by:Carl Tawn
ID: 39721159
But are you overwriting the contents of the array in each iteration, or are you reinitializing the array each time.

i.e. Are you doing:
string[] stuff = new string[10];

for ( ... )
{
    stuff[0] = "something";
    stuff[1] = "something else";
    ...
}

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Or are you doing:
string[] stuff;

for ( ... )
{
    stuff = new string[10];
    stuff[0] = "something";
    stuff[1] = "something else";
    ...
}

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Author Comment

by:cycledude
ID: 39721163
1st one ...
0
 
LVL 52

Accepted Solution

by:
Carl Tawn earned 500 total points
ID: 39721166
In that case, as I said originally, you are passing a reference to the same array to each instance, so any changes you make get made to all references.

Use the second version to create a new array for each instance and you should be ok.
0
 

Author Comment

by:cycledude
ID: 39721171
Hi

thanks,  I will try to re-structure the code so that I can re-initialise the array on each iteration...

will let you know how i get on.
0
 

Author Closing Comment

by:cycledude
ID: 39721260
thanks, a little restructuring and it has worked a treat.
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