Question

I’m having some trouble understanding access modifiers; I want to know better when to use what level of access, especially for properties–just links to good tutorials on that subject could be its own question.

But more specifically, I don’t understand why an object bound to a WinForm control has to be public. So I create my object:

public class Foos : List<Foo>
{
}

public class Foo
{
    private int bar;
    public int Bar
    {
        get { return bar; }
        set { bar = value; }
    }
}

then bind it to a DataGridView

public partial class Form1 : Form
{
    private Foos formFoos;

    public Form1()
    {
        InitializeComponent();

        formFoos = new Foos();
        AddFoo();

        dataGridView1.AutoGenerateColumns = true;
        dataGridView1.DataSource = formFoos;
    }

    /// <summary>
    /// generate some test values
    /// </summary>
    private void AddFoo()
    {
        for (int i = 1; i <= 5; i++)
        {
            Foo foo = new Foo();
            foo.Bar = 5 * i;
            formFoos.Add(foo);
        }
    }
}

Works fine. But what if I don’t want to expose Foo.Bar outside my assembly? If I make it internal int Bar I get an empty dataGridView1. If I make it protected I get a compiler error, because of course Form1 is not derived from Foo.

How does a control in a form in my program not match the definition of internal though?

Internal members are accessible only within files in the same
assembly.

General wisdom on how you make these declarations in a systematic way also welcomed.

Answer 1

You should mark the whole Foo class as internal.

This way, the entire Foo class and all it’s members will be invisible outside the assembly.

Form1.dataGridView1 needs Foo.Bar to be public, otherwise it won’t be able to make use of it.

Now, because Foo is already marked internal, it can expose Bar as public with no risk of exposing it outside the assembly.

This should make both Form1.dataGridView1 and you equally happy.

• Please note that by marking Foo as internal, Foos should also change from public to internal because Foos may not have a higher access level than the class it’s derived from.