This was added to provide a simpler way to update the progress bar at specified points in the process, giving a smoother motion to the updating of the progress bar: On these methods I’ve made the updates to the dialog through the use of a dispatcher.
Because the methods that will be updating the progress bar are called from a Background Worker, this is required to stop exceptions being raised by attempting to modify the dialog off of the main UI thread.
But the progress bar and textbox are updated only when the file is read completely.
I followed a few tutorials, such as: https://msdn.microsoft.com/en-us/library/cc221403(v=vs.95).aspx?
class, you can indicate operation progress, completion, and cancellation in the Silverlight user interface.