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In this video we’ll see a new way to run code on a Thread, and start downloading a playlist instead of just one song!
Songs array:
public static String[] songs = {"He’s the Greatest Dancer", "Cut the Cake", "The Groove Line", "Stayin’ Alive", "Give Up the Funk"};
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Using a runnable with a thread is
an easy way to route some of your app's
0:00
heavier traffic off of the main thread,
but it's not the only way.
0:04
There's actually two ways we can
run code on a separate thread.
0:09
We can pass in a runnable to a new thread
object, which we're currently doing,
0:13
or we can extend the thread class and
override its run method.
0:18
Let's refactor our code to
instead use this second method
0:23
of extending the thread class.
0:26
Let's start by creating a new
class called DownloadThread.
0:29
And let's make it extend the thread class.
0:38
Then let's override the run method
of our new DownloadThread class by
0:42
hitting Ctrl+O to bring up the override
dialog and then selecting the run method.
0:47
Then instead of calling super.run, let's
call our downloadSong method instead.
0:55
Let's cut the method out of MainActivity,
And
1:02
paste it into the bottom of
our DownloadThread class.
1:09
Then let's use Alt+Enter to
create a new tag constant,
1:16
just like we did in MainActivity.
1:20
.class.getSimpleName.
1:25
Next, let's call downloadSong
instead of super.run.
1:30
Lastly, back in MainActivity and
our download button's onClick listener,
1:37
let's get rid of our runnable object,
1:42
And use our new DownloadThread class
instead of the normal thread class.
1:49
Looks good.
1:59
Let's quickly test our app to make
sure it still works the same.
2:01
And success.
2:08
It works just like it did before.
2:12
This code is exactly the same as
when we were using a runnable and
2:15
passing it to a new thread.
2:19
All right, let's take a minute to see
what's going on behind the scenes.
2:22
Let's start by opening the Android
device monitor by clicking up here.
2:27
On the left,
we see a list of running processes,
2:37
and if we expand this list, look at that,
2:42
there's our process right down here.
2:46
Let's click on it and
2:51
then click this button to show all
the threads in our app's process.
2:53
Then if we go back to our app and
2:59
we click on the Download button,
there's our thread.
3:03
And if we click it a bunch,
a bunch of threads.
3:07
If you're ever curious about what's
going on inside your device,
3:14
the Android device monitor is
a great place to start looking.
3:17
Now instead of downloading a single song,
let's say we want to download a playlist.
3:22
In fact, there's an array of songs in
the teacher's notes for us to use.
3:28
Let's go back to the code and
create a new class called Playlist.
3:33
Then, let's copy and
paste the songs array into our new class.
3:48
Making the songs array public static
means we'll be able to access it from
3:55
anywhere in our app.
3:59
Let's close this file and
head over to our DownloadThread class.
4:03
Let's also minimize the log.
4:09
The last thing we need to do is
call the downloadSong method for
4:13
each song in our playlist.
4:17
Sounds like a good place for
a for each loop.
4:19
Inside the run method, lets type for
4:23
(String song: Playlist.songs) and
4:27
then let's add our curly brackets
around the download song method.
4:31
Before we test this, let's take a minute
to talk about what would happen if we
4:41
instead added our loop around the code and
our download button's onClick method.
4:46
If we looped here,
we would create a new thread for
4:55
each song, and all the songs would
be downloading at the same time.
4:59
You'd think this would be great, but by
trying to download all the songs at once,
5:04
we'd be giving our users a bad experience.
5:10
They want to listen to their playlist as
soon as possible, and we've only got so
5:13
much bandwidth we can use for downloads.
5:18
So if we're spreading that bandwidth
out over the whole playlist,
5:21
they'll have to wait a long time
before they can listen to any song.
5:25
It would be better if we downloaded
the songs one at a time.
5:30
This way, our users can start
enjoying their music a lot quicker.
5:35
All right, now let's test our app and
see what happens.
5:40
I'll click the download button and
in ten seconds, we can start
5:48
to see our songs finish downloading one
after the other, just like we wanted.
5:53
We've got our playlist and we're
downloading the songs one at a time, but
5:59
there's still more work to be done.
6:03
In the next video, we'll learn about some
potential errors and how to fix them.
6:05
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