The most important role for asynchronous tasks on Android, as we’ve discussed, is to relieve the UI thread from long-running operations. This calls for defining an execution environment, creating the task to do the long operation, and finally determining how the UI thread and the background threads communicate. All of these properties are encapsulated in an
AsyncTask to make asynchronous execution as easy as it gets.
This chapter gets into the details of
AsyncTask class and shows how smoothly it can handle background task execution, but also raises concerns about the pitfalls you need to watch for.
As the name indicates, an
AsyncTask is an asynchronous task that is executed on a background thread. The only method you need to override in the class is
doInBackground(). Hence, a minimal implementation of an
AsyncTask looks like this:
// Implement task to execute on background thread.
The task is executed by calling the
execute method, which triggers a callback to
doInBackground on a background thread.
AsyncTask finishes executing, it cannot be executed again—i.e.,
execute is a one-shot operation and can be called only once per
AsyncTask instance, the same behavior as a
In addition to background execution,
AsyncTask offers a data passing mechanism ...