Progressbar pendant ouverture d'une image C#

public Form1() 
        { 
            InitializeComponent(); 
            pictureBox1.LoadProgressChanged += new ProgressChangedEventHandler(pictureBox1_LoadProgressChanged); 
            pictureBox1.LoadCompleted += new AsyncCompletedEventHandler(pictureBox1_LoadCompleted); 
        } 

        void pictureBox1_LoadCompleted(object sender, AsyncCompletedEventArgs e) 
        { 
             
        } 

        void pictureBox1_LoadProgressChanged(object sender, ProgressChangedEventArgs e) 
        { 
            progressBar1.Value = e.ProgressPercentage; 
        } 

        private void button1_Click(object sender, EventArgs e) 
        { 
            string ur = "http://photojournal.jpl.nasa.gov/jpeg/PIA11734.jpg"; 
            pictureBox1.LoadAsync(ur); 
        }