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In this video we'll see how to use our newly creating AsyncTaskLoader instead of an AsyncTask!
Related Links
- Loaders Developer Guide
- Threading and Loaders - Android Performance Patterns Video
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We just finished creating our loader,
but we still haven't seen how to use it.
0:00
But before we get to that,
0:04
it looks like I forgot to delete
this percentProgress line.
0:06
So let's do that.
0:09
Okay, now it's time to get back
to deleting our AsyncTaskClass.
0:12
Over in MainActivity, let's start
by deleting our AsyncTaskClass.
0:16
And let's also delete this
new MyAsyncTask line.
0:23
Next, we need to implement a few callbacks
to help us interact with our loader.
0:32
Specifically, we need to
implement LoaderCallbacks, and
0:37
make sure we're picking the option
from the support library.
0:42
And let's use a bitmap array for
our type parameter again.
0:47
Then let's use Alt+Enter to implement
the three required methods.
0:53
The first method is onCreateLoader.
1:00
In this method, we need to create a new
instance of our loader and return it.
1:03
So since our loader requires
a URL as a parameter,
1:08
let's first cut and paste the URL
code into the top of this method.
1:11
Then, right below the URL,
let's return a new instance of our loader.
1:23
return new MyAsyncTaskLoader, and
1:29
passing in this for
the context and url for the URL.
1:33
I'd love to get rid of this
return null as well, but
1:43
even though our URL isn't malformed,
we've still gotta catch the exception,
1:46
which means we need to
have a return down here.
1:51
Well.
Moving on to onLoadFinished,
1:54
this method is called when your work is
done and is where we should update the UI.
1:57
So let's first update the data,
our adapter is based on.
2:02
myAdapter.bitmaps = data.
2:08
And then let's notify our adapter
that the data has been updated.
2:13
myAdapter.notifyDataSetChanged.
2:18
Nice.
2:21
The last method is onLoaderReset.
2:22
If your loader's been reset,
then it no longer contains any data.
2:26
So if you've got any references
to data in your loader,
2:30
you'd want to clean
those up in this method.
2:33
Since we don't have any way to reset our
loader, we're fine leaving this empty.
2:36
Now that we've implemented
our loader callbacks,
2:41
all that's left is to start our loader.
2:43
At the bottom of onCreate.
2:45
Let's call
getSupportLoaderManager().initLoader().
2:51
Then let's pass in an arbitrary number for
the ID, I'll choose 1.
3:01
And an arguments bundle, which we don't
have, so let's just pass in null.
3:07
And finally a LoaderCallbacks object,
3:12
which we've implemented
right here in this activity.
3:14
So let's just pass in this.
3:17
And before we forget, let's make sure to
show our progress bar while we're loading
3:22
and hide it once we're done.
3:26
So at the top of OnCreateLoader,
3:28
let's add progressBar.setVisibility
to View.VISIBLE.
3:32
And then at the top of onLoadFinished,
Let's set it to gone.
3:39
progressBar.setVisibility(View.GONE); All
right, time for the moment of truth.
3:45
Let's run the app and see what happens.
3:55
There's our progress bar, and
now we've got our images.
4:02
And if we rotate the app,
Awesome, it's the same images!
4:06
So instead of re-downloading all of those
images, we just used our cached images and
4:13
made for a much better user experience.
4:18
When you've gotta do something
in the background and
4:22
you're worried about the activity
lifecycle, just use a loader.
4:24
Since a loader will stay alive
through a rotation, it's a great
4:28
place to do your loading and keep any data
safe from being destroyed in an activity.
4:30
If you'd like to learn more about loaders,
check out the teacher's notes below.
4:35
And as always, if you've got any questions
or would like to try your hand at
4:39
answering someone else's question,
be sure to check out the community.
4:42
Until next time.
4:46
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