Call a method from another class

Question

I'm wanting to know how I can call a method from another class without having to make a new instance of that class. I've looked up this and 90% of the examples I see require me to make a new copy of my referenced class.

Something like this:

Fooclass test = new Fooclass();
test.CallMethod();

However, I'm wondering if there is a way I can call the method without making a new class instance. Right now I've tried the following in unity.

public ImageLoader image; 
void Start () 
{
    image = gameObject.GetComponent<ImageLoader>() as ImageLoader;
}

void OnClick()
{
    image.MoveForward();
}

however, when I run this I get the following error:

NullReferenceException: Object reference not set to an instance of an object

i know this would be settled with making a new instance of my image loader class but I can't do that as it is holding a lot of data I don't want duplicated multiple times.

Answer 1

Yes you can. The first way is to make your class to be static.

public static class Fooclass
{
    // I don't know the return type of your CallMethod, so I used the void one.
    public static void CallMethod()
    {

    }
}

This way, whenever to your code you can call the CallMethod() like the following:

Fooclass.CallMethod()

Another apporach it would be to define a static method in your current class, without the class needed to be static, like the following:

public class Fooclass
{
    // I don't know the return type of your CallMethod, so I used the void one.
    public static void CallMethod()
    {

    }
}

Now since all the instances of the Fooclass would share the same method called CallMethod, you can call it like below:

Fooclass.CallMethod()

without again needed to instantiate an object of type Fooclass, despite the fact that now Fooclass isn't a static class now !

For further documentation please take a look to the link Static classes and Static Members.