对象寻址/访问问题中的C＃列表

Question

I've got some code. I have a class:

public class TestClass
{
    private string String1 = "";
    private List<string> Strings = new List<string>();

    public TestClass(string String1, List<string> Strings)
    {
        this.String1 = String1;
        this.Strings = Strings;
    } // end constructor.

    // Associated get/set methods.
} // end class.

I then have (in another class, some code which uses this):

public TestMethod()
{
    List<string> Strings = new List<string>();
    List<TestClass> MasterList = new List<TestClass>();
    int Counter = 0;
    string Name = " ... " // <- updated every time.

    while(Condition1)
    {
        if(Condition2)
        {
            Strings.Add(Counter.ToString());
        }
        else
        {
            MasterList.Add(new TestClass(Name, Strings));
            Name = // ... <- name updated here.
            Strings.Clear(); // Clear array.
        } // end if.
    } // end while.
} // end method.

The first time, the first element of MasterList is "Name1" and the list contains "1, 2, 3". The next time, the MasterList contains "Name2" and "4, 5, 6" but the first element now contains "4, 5, 6" and not "1, 2, 3". When running for some time, the "Name1", "Name2" gets updated every time but every elements list is exactly the same contents, for example, what should be the output:

"Name1" -> "1, 2, 3" "Name2" -> "4, 5, 6" "Name3" -> "7, 8, 9"

What actually happens:

"Name1" -> "7, 8, 9" "Name2" -> "7, 8, 9" "Name3" -> "7, 8, 9"

Trying to figure out what I've done wrong here, any ideas? Is this some kind of reference issue?

Thanks! Jonathan

Answer 1

You are reusing the same list all the times:

MasterList.Add(new TestClass(Name, Strings)); //<<- Strings is always the same instance

So any change you do on the list will be propagated to all the child classes, a List is a reference object, so when you pass it to a function you don't pass a structure of data but a reference to the object, thus all the classes point to the same object.

A very simple way of solving this is to replace:

Strings.Clear(); // Clear array.

with:

Strings = new List<string>();

In this way you will pass the reference to a new instance each time.