static classes don't work as advertised

Question

I am new to C#.  In C, you can have global variables.  In C#, I read that I can use a static class instead.  So I created one as follows:

 public static class Class1

    {

        static private int uc;

            public static int urlcount

            {

                get

                {

                    return uc;

                }

                set

                {

                    uc = value;

                }

            }

        

    }

And I use this class as follows:

            Class1.urlcount = (int)(this.comboBox1.SelectedValue);

The problem is that I get a message that "object reference not set to an instance of an object".

This seems to mean I should have instantiated the class, but since its static, why bother?

Any help is appreciated.

Answer 1

The problem here is that SelectedValue is null. Use SelectedItem instead.

Answer 2

check the RHS of the assignment, make sure (int)(this.comboBox1.SelectedValue); resolves to a valid integer. also check the value of comboBox1 and make sure it is not null.

the following works fine:

 

Class1.urlcount = 10;