mymn.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace TagGocNhin
{
    enum State
    {
        Stop, Playing, Paused
    }

    public partial class TagGocNhin : Form
    {
        State s; 

        public TagGocNhin()
        {
            InitializeComponent();
        }

        private void btnPlay_Click(object sender, EventArgs e)
        {
            if (s == State.Stop)
            {
                s = State.Playing;
                btnPlay.Text = "Playing";
            }

            if (s == State.Playing)
            {
                s = State.Paused;
                btnPlay.Text = "Click to play..";
            }

            MessageBox.Show(s.ToString()); 
        }

        private void TagGocNhin_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (e.Handled && e.KeyChar == (char)Keys.Space )
            {
                btnPlay.PerformClick(); 
            }
        }
    }
}