Question

I have Form and Class like that :

namespace ALTER_Control
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            ALTER A = new ALTER();
            A.ALTER();
        }
    }

    public class ALTER
    {
        public Form1 F;
        public void ALTER()
        {
            F.TextBox1.Text="I Altered That";
        }
    }
}

So i try to call ALTER() to change the textbox1 value in Form1 but i get that error :

object reference not set to an instance of an object

That happens only if i am accessing or modifying the Form1 Controls.

And by the way i set textbox1 modifier to public

So , finally i`d like to change the control value without getting that error.

Answer 1

You need to assign the reference to the form. Like this:

    private void button1_Click(object sender, EventArgs e)
    {
            ALTER A = new ALTER();
            A.F = this;
            A.ALTER();
    }