更改对象数组中的一个元素会更改所有元素，C＃，如何按值分配对象

Question

I'm new to c#, and I think I'm confused about how to assign objects by value rather than reference. In the following code, I have a constructor taking a default object for the posGrid to be filled with. I want these all to be merely copies of the default object, but when I change one, they all change. I assume this is because I'm initializing the array with references to the object, but how do I assign them just the value?

public Grid (int width, int height, Unit defaultUnit)
{
    Random rand = new Random();
    this.width = width;
    this.height = height;

    posGrid = new Unit [height, width];
    for (int y = 0; y < height; y++)
        for (int u = 0; u < width; u++)
            posGrid[y, u] = defaultUnit;
}

Answer 1

Variable types

Variables like int, long are value types and have it's own memory space and contains the value.

Reference types

Variable values of string, class .. are not directly stored. The value is stored in a other memory space and a pointer stores this adress and is pointing to it.

Solution

So for your problem you have so create a new Unit based on the values of defaultUnit.

Answer 2

There are many ways you could solve this problem.

The simplest way is to make Unit a struct:

struct Unit { ... }

Since structs are value types, a copy of Unit is automatically created when you assign it to something, as opposed to the reference being copied. However, there might be some features of classes that you want Unit to have (eg having a base class), in which case you need another method.

---

Alternatively, you can add a CreateCopy method:

public Unit CreateCopy() {
    Unit copy = new Unit();
    copy.Property1 = this.Property1;
    copy.Property2 = this.Property2;
    // etc
    return copy;
}

And call it when you create the array:

posGrid = new Unit [height, width];
for (int y = 0; y < height; y++)
    for (int u = 0; u < width; u++)
        posGrid[y, u] = defaultUnit.CreateCopy(); // <----

You can also achieve this by implementing ICloneable .

---

A third method is to have the constructor of Grid accept all the data needed to create the unit as parameters, instead of the Unit object itself. And then the constructor can create the Unit objects on its own.

public Grid (int width, int height, SomeType defaultUnitProperty1, SomeType defaultUnitProperty2)
{
    Random rand = new Random();
    this.width = width;
    this.height = height;

    posGrid = new Unit [height, width];
    for (int y = 0; y < height; y++)
        for (int u = 0; u < width; u++)
            posGrid[y, u] = new Unit(defaultUnitProperty1, defaultUnitProperty2);
}