using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.IO.Ports;


namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        // Add this variable
        string RxString;
        SerialPort serialPort1 = new SerialPort();
        public Form1()
        {
            InitializeComponent();
        }     
        private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            if (serialPort1.IsOpen) serialPort1.Close();
        }

        private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
        {
            // If the port is closed, don't try to send a character.
            if (!serialPort1.IsOpen) return;

            // If the port is Open, declare a char[] array with one element.
            char[] buff = new char[1];

            // Load element 0 with the key character.
            buff[0] = e.KeyChar;

            // Send the one character buffer.
            serialPort1.Write(buff, 0, 1);

            // Set the KeyPress event as handled so the character won't
            // display locally. If you want it to display, omit the next line.
            e.Handled = true;
        }

        private void DisplayText(object sender, EventArgs e)
        {
            textBox1.AppendText(RxString);
        }

        private void serialPort1_DataReceived
          (object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
        {
            RxString = serialPort1.ReadExisting();
            this.Invoke(new EventHandler(DisplayText));
        }

        private void button_start_Click(object sender, EventArgs e)
        {
            serialPort1.PortName = "COM3";
            serialPort1.BaudRate = 9600;
           
            serialPort1.Open();
            if (serialPort1.IsOpen)
            {
                button_start.Enabled = false;
                button_stop.Enabled = true;
                textBox1.ReadOnly = false;
            }
        }

        private void button_stop_Click(object sender, EventArgs e)
        {
            if (serialPort1.IsOpen)
            {
                serialPort1.Close();
                button_start.Enabled = true;
                button_stop.Enabled = false;
                textBox1.ReadOnly = true;
            }
        }
    }
}