Sunshine in the Background - Developing Android Apps

10-02 Sunshine in the Background

Remember back in lesson two
when Katherine used

an AsyncTask hooked up to
a refresh button to update our data?

Rato talked about how
that was a bad idea

because the AsyncTask is not tied
to the activity life cycle.

The virtual machine will hold on
to the activity object

as long as the AsyncTask is running,
even after Android

has called onDestroy for the activity
and expect it to be discarded.

If you rotate your phone,
the behavior is to destroy

your activity and instantiate a new one.

The naive AsyncTask implementation
now has two threads

trying to perform the same update,
and so forth.

The point is, it's not
the best pattern

for a potentially
very long background operation,

such as fetching from web services.

If you leave the app,
the AsyncTask will continue to run

for as long as your process is kept alive,

but will run at a low priority,
and your process

will be the first thing
to be killed if the device

needs more resources.

And there's a bigger problem.

Your app has to be visible
and running in the foreground

to instantiate the task
in the first place.

Because we started a task,

to update the weather
when we started the app,

this can have undesirable behavior
if the weather changes rapidly.

So now we're going to learn
the right way to perform updates.

We'll want to automate
the process while the app

is in the foreground.

But even more importantly,
we want the app to get

regular updates in the background
with minimal battery drain.

That will be especially important
later in this lesson

when we introduce
weather notifications.