按下按钮时增加一个项目，Unity

Question

I am trying to increment an item in Unity when a button is pressed. I set the item value like so item = shells; where shells are another variable that I set earlier in my code. I am doing it in this way so that I can change the item value to something else later on like item = fossils; .

The problem is that unless I have it as shells++; nothing will happen when I press the button.

current code:

public double shells; 

public addItem(){
item = shells; 
item++; 

this code does not do anything when the addItem method is called.

Code that works

public double shells; 

public addItem(){
shells++; 

If there is a better way of doing this please let me know.

Answer 1

The problem here is that you're dealing with "value types". The code you have in your first example is assigning item the value of shells . Once you do that, you have two variables - item and shells . When you increment the item value ( item++ ), you're ONLY incrementing the item variable. So now item will have a value 1 greater than shells .

What you COULD do if you chose, is this:

public double shells; 

public addItem()
{
    item = shells; 
    item++;
    shells = item; // here, you're assigning shells the value of item.
}

The code itself is kind of pointless, but it demonstrates how you would get a modified value back into the original variable.

Here's Microsoft's page describing "value types". It'll be beneficial for you to understand the difference between "value types" and "reference types" going forwards.