A thread sometimes also needs to communicate with the UI thread, either in between the execution of the thread or at the end of the execution of a thread. Only objects running on the UI thread have access to other objects on that thread. Because tasks that you run on a thread from a thread pool aren't running on your UI thread, they don't have access to UI objects. For example, if you have the task of downloading a large file from a server, then showing the progress of the download would be a good practice. In order to show this progress, your thread must communicate with the UI thread to display the progress as a percentage.
Data from a background thread could communicate with the UI thread using a Handler ...
