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Threads in Android
7:46In this video we’ll talk about what we’re trying to accomplish, and then we’ll create our project!
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Hi, I'm Ben and in this course we're going
to learn all about threads and services.
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One type of app that makes extensive use
of threads and services is a music player.
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We won't be making
a full-fledged music player,
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that would be way too much work for
this course.
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But at the end of this course,
you will have an app that plays a song.
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More than that though, you'll have
an excellent understanding of threads and
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services in Android.
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I'll cover everything you need to know.
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So let's get started.
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First, we'll need to create a project.
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Let's create a new project
called Music Machine.
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And let's leave everything else default.
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Except let's choose empty activity,
instead of blank activity.
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And then hit Finish.
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The first thing we want our music machine
to do is be able to download songs from
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the Internet.
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Let's start by adding a download button.
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Let's switch over to activity main,
and delete this Hello World text view.
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Then let's add a button to the bottom
of the layout, centered horizontally.
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This will be the download button.
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So let's give it an ID of download button.
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And change its text to say Download.
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Lastly, let's give our button a width
of match parent, by clicking up here.
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Great, let's switch back
to our activity and
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declare our button as a field
at the top of our class.
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Let's call it mDownloadButton.
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Private Button
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mDownloadButton.
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Then let's initialize this button and
the bottom of onCreate.
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MDownloadButton = findViewByID
R.id.downloadButton.
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Alt+Enter to add the cast.
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Next up, let's add
an OnClickListener to our button.
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Add a couple of lines to
the bottom of onCreate, and
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we'll type mDownloadbutton.set
OnClickListener, new OnClickListener.
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Now let's implement the on click
method for our download button.
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Inside the OnClick method, let's start
with a toast that says downloading.
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Make sure to pick the Create
a new Toast option,
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then hit Enter to move to the text
parameter, and write Downloading.
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Then, let's make a call to a new
method called downloadSong.
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And let's use alt + enter to create this
method inside our MainActivity class.
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Inside the download song method,
ideally, we would download a song,
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but since downloading can be tricky and
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isn't the point of this course,
we'll just pretend to download.
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So instead of downloading a song,
let's just have this method wait
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ten seconds to simulate about how long
it might take to download a song.
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An easy way to do this is to add
ten seconds to the current time and
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then run a while loop until
our ten seconds are up.
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We can get the current time
by using the system from
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the Java Lang
class.currenttime.Millis method.
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This method returns the difference
measured in milliseconds
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between the current time and
midnight January 1st, 1970.
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This might seem like
a weird way to do this, but
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it actually makes working
with time super easy.
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Instead of juggling hours,
minutes, seconds, and whatever,
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we only need to worry about one number.
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Let's start by declaring
a variable called end time.
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Which will represent a time ten seconds
after when download song is called.
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But instead of using an Int,
we'll need to use a long.
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There's been a lot of
milliseconds since 1970.
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Let's type long endTime and
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set it equal to system.currenttimemillis
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+ 10 x 1000.
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There's 1000 milliseconds in a second so
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adding 10 x 1000 is adding 10
seconds to the current time.
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We could use 10,000,
instead of 10 times 1,000, but
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writing it this way makes it easier to see
at a glance how much time we're adding.
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Now that we've got our end time,
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let's set up a while loop to run while
the current time is before the end time.
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While system.currentTimeMillis
less than endTime and
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then let's add our brackets.
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Nice, this will definitely work,
but we can do better.
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Right now it's checking the current
time against the end time thousands
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of times a second and
that's a huge waste of processing power.
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Instead, inside the body
of our while loop,
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let's wait one second before looping.
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We can do this by using
the Thread.sleep method.
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And if we pass on a parameter,
that's how many milliseconds
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we'll wait, or sleep, before continuing.
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Let's pass on 1,000 to wait for
one second.
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Then, we can see that this sleep command
might throw an interrupted exception.
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So let's use Alt+Enter to wrap
this in a try catch block.
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Lastly, let's add a log message
to the end of our download song
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method that says song downloaded.
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Let's type log.d TAG and all caps.
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Song downloaded.
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Alt+Enter to importLog and then let's use
Alt+Enter to create our TAG constant.
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And let's set it equal to
MainActivity.class.getSimpleName.
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We're all set up to start exploring
the world of threads and services,
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in the next video we'll run this and
see where we can make some improvements.
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