A status bar is the bar showing signal, battery and time on the top of the phone‘s screen. In WP8.1 we it‘s called status bar, but in WP8.0 it‘s called phone shell.

Show progress bar in the status bar:

            var statusBar = Windows.UI.ViewManagement.StatusBar.GetForCurrentView();

            //statusBar.ProgressIndicator.ProgressValue = http://www.mamicode.com/0.5;

            statusBar.ProgressIndicator.Text = "loading";

            statusBar.ProgressIndicator.ShowAsync();

Hide progress bar in the status bar:

            var statusBar = Windows.UI.ViewManagement.StatusBar.GetForCurrentView();

            //statusBar.ProgressIndicator.ProgressValue = http://www.mamicode.com/0;

            statusBar.ProgressIndicator.HideAsync();

A useful link: http://blogs.msdn.com/b/amar/archive/2014/05/12/status-bar-in-windows-phone-8-1.aspx

WP 8.1 status bar