C# textBox1,只能輸入0~9，一個小數點，Backspace ，ENTER

        private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
        {
            
            if (e.KeyChar == (char)Keys.Back||e.KeyChar==(char)Keys.Enter)
            {
                return;
            }            

            if (e.KeyChar == '.')
            {
                foreach (char i in textBox1.Text)//判定textBox1是否有小數點
                {
                    if (i == '.')
                        e.Handled = true;//有
                }
                return;
            }

            if (e.KeyChar < '0' || e.KeyChar > '9' )
            {
                e.Handled = true;
            }
        }