We just got an ANR by trying to do our downloading in our service.

But didn't we just say that services are an application component

that can perform long running operations in the background?

What gives?

Well, by default,

everything in an app runs on the main thread, including our service.

So even if a service is performing long running operations in the background

by default it will be doing those long running operations on the main thread.

If we want our service to do work on a separate thread,

we need to create that separate thread ourselves.

Seems simple enough.

Now let's make our download service do the downloading on a separate thread.

Let's close the Android manifest and start with some planning.

On the left is the code from when we created our own thread and main activity.

We created, named, and started the thread in the on create method.

Then, in the on click method of our button for each song we obtained and

set a message and then sent that message using our handler.

Now we need to replicate this in our service.

Just like an activity, a service also has a life cycle and life cycle methods.

And one of these methods is the good or onCreate method.

So we'll create, name and start our thread, in the onCreate method.

And since we've now replaced this message part with starting our service,

we should now be obtaining and

sending messages to our handler over here in the onStartCommand method.

All right.

Let's start and download service and remove the download song method.

We'll now be using our download handler and

it still has its download song method from before.

Let's also remove the call to download the song.

Then let's override our services on create method.

Let's place our cursor above onStartCommand and

use control O to override the onCreate method.

And let's delete this call to super.

We don't need it.

Now we need to create, name and start our thread just like we did in our activity.

Let's start by creating a new download thread at the top of the on create method.

Download thread thread equals new download thread.

Then on the next line, let's set the name of our thread.

Thread.setName DownloadThread.

And lastly let's start our thread, thread.start.

Next up, we need to send a message to our thread

each time on start command is called.

Under where we declare a song, let's obtain a message, and

set it to a new message variable.

Message message equals message.obtain.

Then let's attach our song variable to our message,

message.obj equals song,

and send the message using our handler, which we currently don't have access to.

Let's quickly create a field for our download handler.

private download handler

mhandler, then let's give it a value at the bottom of on Create

mhandler equals thread but mhandler.

Lastly, back in on StartCommand,

let's send our message, mHandler.sendMessage(message);,

great work!

Now that we're doing our download and a separate thread,

again we shouldn't have any issues with the app being slow or

not responding, but let's test it out just to be sure.

Let's click the download button and

yikes the app crashed If we look through the log.

And filter by errors.

It looks like we're getting a null pointer exception because we're trying to invoke

the virtual method, send message on a null object reference.

And if we click on the link to jump to the error

it looks like that null object is our handler.

Just like last time this is because our main thread

is ahead of our download thread.

The main thread has already finished the onCreate method and

moved on to the onStartCommand method all

before our download thread has even created our download handler.

To fix this,

let's make our main thread wait until the handler exists before we assign it.

Up in the on create method above the assignment

to mHandler,let's type while thread.m

handler equals null and add our brackets.

We shouldn't have to worry about a null handler any more.

Using an empty while loop like this definitely isn't the best practice.

But it's the best we can do with what we've learned so far.

Now let's test the app again and hopefully everything will work.

Also make sure you have the Android device monitor open so

we can see what happens when we kill our app's process.

And if we click the download button, it seems to be working.

And if we wait ten seconds, We can see our downloads start coming in.

Nice.

Now let's switch to the Android device monitor and kill our apps process

and if we check the log and scroll up a little bit,

we can see a scheduling restart of crashed service and there's our service.

It looks like it'll restart in 47 seconds.

So let's wait for 47 seconds and see what happens.

And look at that, our process came back.

And check it out.

Our downloads are happening again.

What's going on here?

Let's find out in the next video.