Question

Is it bad practice to put most variables at class level in a Form? Would these be considered global variables?

public partial class Form1 : Form
{
    private string mode;
    private int x, y;

    public Form1()
    {
        InitializeComponent();
    }
}

I’m using the variables in multiple controls when I declare them at class level.

Answer 1

Those would be considered class-level globals (to distinguish from application globals.) The more important distinction in this case is that they are private to the class.

Class-level globals have their uses, so I definitely wouldn’t call it a bad practice. A very good use for private class globals is when you plan to expose them through property accessors. For example:

• public readonly properties whose values are controlled by logic internal to your class.

• public properties with both set and get accessors (enabling custom validation logic in setter.)

However, I would say it’s a good practice to make things local unless otherwise necessary. The reason is that you have less mutable state belonging to a class instance, so there is less potential for bugs like this:

private int EvilMethod1() {  
    x = (int) Math.Pow((double) y, 2);
    return x;
} 

private int EvilMethod2() {  
    y = (x + y) * 2;                    
    return y;
}

// Assignments depend on the current values of x and y, 
// as well as yielding unexpected side effects.
private void PureEvil()
{
    // Return value depends on current y; has side effect on x while assigning y.
    y = EvilMethod1();  

    // Return value depends on current x and y; has side effect on y while assigning x.
    x = EvilMethod2(); 
}