Label update

Hi everyone,
i am new on android, what is my wrong?
i see just Done on screen after 10 seconds, i want to see , Progress : 10%,Progress : 20% etc...

lbl.Text = "Starting";
for (var i = 0; i<10;i++)
{
System.Threading.Thread.Sleep(1000);
activity.RunOnUiThread ( () => {
lbl.Text = String.Format ("Progress : {0}0%", i+1);
});
}
lbl.Text = "Done";