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Creating the Service6:11 with Ben Deitch
In this video we introduce bound Services and also talk about the Service lifecycle!
[MUSIC] 0:00 So far, we've only seen one type of service started, but 0:04 remember there's two ways we can use a service. 0:09 In addition to starting a service we can also bind to a service. 0:13 Binding to a service is for 0:17 when we need to interact with our service in more ways than just starting it. 0:19 If we want to communicate with our service after starting it, 0:24 we'll need to buy into it. 0:27 If you're familiar with the client server model, 0:30 abound to service can be thought of as the server. 0:32 And the activity binding to that service can be thought of as the client. 0:36 A good example would be a service used for music playback. 0:40 Once the service is playing music, 0:44 there's all kinds of things we could want to tell it. 0:47 Like, play a song or skip to the next song. 0:49 Let's get started with bound services by adding the ability to play songs 0:54 to our music machine app. 0:58 First, let's create a new class for 1:00 music playing service and let's name it Player Service. 1:03 Then, let's make it extend to the service class and 1:12 use alt enter to implement the required on-bind method. 1:18 All right, before we go on, let's head over to our Android manifest and 1:24 declare our new service, use command or control D to duplicate 1:30 and change download intent service to player service, and we're done. 1:37 Let's also take this opportunity to get rid of some of the tabs we won't be 1:44 needing for a while. 1:48 Let's close all of our classes that start with download as well as the Android 1:50 manifest. 1:54 Now that we've got our service, let's take a minute to go over what we'll be doing. 2:00 The goal is for us to be able to play and pause a single song using a bound service. 2:05 Doing this with a service is what will allow us to have music playback in 2:12 the background, even when our activity is closed. 2:15 However, music playback is not the goal of this course. 2:20 So I won't be going into too much detail about it. 2:24 Sounds like we need a song. 2:28 That's why I put one in the teacher's notes below. 2:30 Go ahead and download it. 2:33 Then let's create a new resource directory named Raw where we can store our MP3 file. 2:35 Right click on the res directory, New, Android Resource Directory, 2:43 pick Raw as the resource type and then hit OK. 2:50 Then let's copy and paste the song into our new raw directory. 2:59 Copy. 3:06 Paste. 3:09 And now we'll be able to use this song in our code. 3:12 Cool. 3:15 Back in our player service class we'll be using a media player object 3:17 to handle playing and pausing our song. 3:21 Let's create a new field for our media 3:25 player by typing private media player, M player. 3:30 Now to initialize it. 3:37 We only need one media player, so where should we create it. 3:41 Well, to answer that question, 3:45 we need to have a better understanding of the service lifecycle. 3:48 Luckily, the lifecycle of a service is much simpler than that of an activity. 3:52 For a Started service [SOUND] we start with the call to startService [SOUND]. 3:57 Then if our service hasn't been created yet, its onCreate [SOUND] method is 4:01 called followed by a call [SOUND] to onStartCommand. 4:05 And when a Started service is stopped, it's onDestroy method will be called. 4:09 For a bound service we start with a call to bindService, then if our service hasn't 4:14 been created yet it's onCreate method is called, followed by a call to onBind. 4:20 Once all the clients from our bound service have unbound 4:26 the onUnbind method will be called followed by one final call to onDestroy. 4:30 We can also have a service that is both started and bound, which means onStart 4:36 Command was called, and there's at least one client still bound to the service. 4:41 In this case on destroy won't be called until the service has been stopped and 4:47 all of the clients have on bound from the service, that wasn't so bad, right? 4:53 Back to the question, where should we initialize our media player? 4:58 Well, we only need one media player. 5:02 So, we probably shouldn't initialize end on bind. 5:06 Since on bind is called each time a client binds to our service. 5:09 Rather let's initialize it and 5:14 on create which is only called once during the life cycle of a service. 5:16 Let's add some space above on bind, and 5:21 use control O to open the over ride dialog. 5:24 Then let's override the on create method and 5:28 get on with an initializing our media player. 5:32 Let's get rid of this call to super.oncreate, 5:36 calling super isn't required for the service lifecycle. 5:39 Then let's type mPlayer = MediaPlayer.create, 5:43 pass in our context by using the this keyword, and pass in our resource ID for 5:51 the song, R.raw.jingle, voila! 5:57 In the next video will see how we can use this media player to play and 6:05 pause our song. 6:09
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