input validation after if statement
===

When trying a regular expression for no characters my winforms EnterValue is still being triggered after the if statement, how can I stop it from going any further after the trigger?

        private void EnterValue_Click(object sender, EventArgs e)
        {
            if (textBox1.Text != string.Empty && !Regex.IsMatch(textBox1.Text, @"^[0-9]+$"))
            {
                MessageBox.Show("Please only enter numbers");
                textBox1.Clear();
            }

            //convert input to double
            listDouble.Add(Convert.ToDouble(textBox1.Text)); // this line still throws exception
            textBox1.Clear();
            //clear existing items
            listBox1.Items.Clear();
            // clear any existing list items
            for (int i = 0; i < listDouble.Count; i++)
            {
                listBox1.Items.Add(listDouble[i]);
            }
            //for each value added, add this to our list 
        }