Restricting Input to Numbers Only In Textbox? (c#)

Question

Please excuse me for asking this, I have looked at various different questions relating to this and I still can not get it to implement.

Using the answers I have looked at, I have gathered this, and applied this coding to my text box.

private void TxtBox5_KeyPress(object sender, KeyPressEventArgs e)
    {
        if (!(Char.IsDigit(e.KeyChar) || (e.KeyChar == (char)Keys.Back)))
            e.Handled = true;
    }

Now, when I proceed to run the program, I am still able to enter letters into it. I do not know what to do next, so any solution would be great. thanks.

Answer 1

Okay this is what i made just now, it works 100% just tested it.Note that my textBox is named serialTxtBox, you can change it to yours.

void serialTxtBox_TextChanged(object sender, EventArgs e)
        {
            bool enteredLetter = false;
            Queue<char> text = new Queue<char>();
            foreach (var ch in this.serialTxtBox.Text)
            {
                if (char.IsDigit(ch))
                {
                    text.Enqueue(ch);
                }
                else
                {
                    enteredLetter = true;
                }
            }

            if (enteredLetter)
            {
                StringBuilder sb = new StringBuilder();
                while (text.Count > 0)
                {
                    sb.Append(text.Dequeue());
                }                

                this.serialTxtBox.Text = sb.ToString();
                this.serialTxtBox.SelectionStart = this.serialTxtBox.Text.Length;
            }
        }

EDIT: Definitely you are doing something wrong. In your form constructor which is named like your form. In my case SerialGenerator, you need to initialize the event. In my case :

public SerialGenerator()
        {
            InitializeComponent();
            this.serialTxtBox.TextChanged += serialTxtBox_TextChanged;
        }

this will fire the method everytime someone enters something in your textBox. Make sure you rename it to your textbox's name