delegate void PropertyChange();

class SomeClass
{
    public event UI UserEvent;
    void OnUserEvent()
    {
        UserEvent();
    }

    private String someVal;
    public String SomeVal{
        get {}
        set
        {
             someVal = value;
             OnUserEvent();
        }
    ....
}

public Form1()
{
    InitializeComponent();
    CasesFileSystem.UserEvent += new UI(onChange);
}

private void onChange()
{
    textBox1.Text = "ffuuuuuu";
}