public partial class Form1 : Form    {        public Form1()        {            InitializeComponent();        }               private void button1_Click(object sender, EventArgs e)        {            CheckForIllegalCrossThreadCalls = false;            this.label1.Text = "aaaaa";                     Thread tr = new Thread(testc);            tr.Start();        }        private void testc()        {            for (int i = 0; i < 10; i++)            {                Thread.Sleep(10000);                MessageBox.Show("a");            }        }    }