1 00:00:05,500 --> 00:00:06,800 Welcome back, everyone. 2 00:00:06,800 --> 00:00:11,300 Did I really say we were going to start improving our app at the end of the last video? 3 00:00:11,960 --> 00:00:16,260 Well, we were but then Google released version 2.2.0 4 00:00:16,510 --> 00:00:19,870 of lifecycle-viewmodel-ktx. 5 00:00:21,070 --> 00:00:24,430 One of the new features concerns coroutines in a ViewModel. 6 00:00:25,330 --> 00:00:28,330 As we are using coroutines in our ViewModels, 7 00:00:28,630 --> 00:00:30,730 we've added these next few videos. 8 00:00:31,720 --> 00:00:34,620 We originally changed the app to use coroutines 9 00:00:34,620 --> 00:00:36,220 while they were still experimental. 10 00:00:37,100 --> 00:00:39,460 Then they became part of the Kotlin language, 11 00:00:39,460 --> 00:00:44,160 no longer experimental and Jetbrains have been improving them ever since. 12 00:00:45,060 --> 00:00:47,360 One thing you'll now find online 13 00:00:47,660 --> 00:00:50,660 is a suggestion that using global scope 14 00:00:50,660 --> 00:00:52,260 isn't always a good idea. 15 00:00:53,560 --> 00:00:56,560 Let's have a look at the code, so you can see what I'm talking about. 16 00:00:57,260 --> 00:00:59,560 I'll start with the LoadData function 17 00:00:59,560 --> 00:01:02,160 in our DurationsViewModel class. 18 00:01:04,660 --> 00:01:06,660 On line 191, 19 00:01:06,660 --> 00:01:10,260 we use GlobalScope to launch our coroutine. 20 00:01:10,860 --> 00:01:13,060 That's not necessarily a problem here 21 00:01:13,460 --> 00:01:17,060 because we've only got a single function running asynchronously. 22 00:01:17,720 --> 00:01:20,020 For a discussion about using GlobalScope, 23 00:01:20,420 --> 00:01:23,820 check out a blog post by one of the JetBrains team leads 24 00:01:23,820 --> 00:01:26,820 Roman Elizarov on medium.com. 25 00:01:27,810 --> 00:01:30,410 I'll switch to that page in my browser, 26 00:01:30,410 --> 00:01:33,010 and the link will be in the resources for this video. 27 00:01:35,810 --> 00:01:39,170 It's worth reading this article and some of the others it links to 28 00:01:39,170 --> 00:01:41,870 if you need to understand co routines more fully. 29 00:01:42,370 --> 00:01:46,070 For our purposes, running single functions in the background, 30 00:01:46,070 --> 00:01:48,370 we don't need to go into that level of detail. 31 00:01:49,170 --> 00:01:50,670 At the end of the article, 32 00:01:50,670 --> 00:01:53,670 you'll find a link to Google's coroutines code lab 33 00:01:54,030 --> 00:01:55,630 if you want to learn more about them. 34 00:01:56,620 --> 00:01:58,980 If you're launching coroutines in a ViewModel, 35 00:01:58,980 --> 00:02:01,780 you can now specify ViewModelScope. 36 00:02:02,440 --> 00:02:05,040 ViewModelScope is an extension property 37 00:02:05,040 --> 00:02:07,840 that was added in version 2.2.0 38 00:02:07,840 --> 00:02:10,199 of the androidx lifecycle components 39 00:02:10,699 --> 00:02:14,500 with the stable version being released at the end of January 2020. 40 00:02:15,760 --> 00:02:17,560 To use ViewModelScope, 41 00:02:17,560 --> 00:02:20,760 we need to add another dependency to build.gradle. 42 00:03:02,560 --> 00:03:04,060 Remember to sync now 43 00:03:05,660 --> 00:03:09,260 before attempting to reference this component in your code. Okay. 44 00:03:09,560 --> 00:03:11,360 Back to the DurationsViewModel. 45 00:03:13,260 --> 00:03:17,460 We can now use ViewModelScope rather than GlobalScope. 46 00:03:33,460 --> 00:03:36,360 I'll talk a bit about that Dispatcher later. 47 00:03:36,760 --> 00:03:39,860 We make the same change in the DeleteRecords function 48 00:03:39,860 --> 00:03:41,860 on line 214. 49 00:03:55,960 --> 00:03:58,960 We launch a coroutine in five places 50 00:03:58,960 --> 00:04:00,660 in TaskTimerViewModel. 51 00:04:01,360 --> 00:04:03,620 The first is in the LoadTasks function. 52 00:04:23,820 --> 00:04:27,020 I'll copy that line to the clipboard and then paste it in, 53 00:04:27,020 --> 00:04:28,420 in the other four places. 54 00:04:32,420 --> 00:04:35,120 There are two in the SaveTask function. 55 00:04:47,620 --> 00:04:49,920 There's another one in DeleteTask 56 00:04:56,520 --> 00:04:59,220 and the last one is in the SaveTiming function. 57 00:05:07,220 --> 00:05:11,220 Using ViewModelScope now that Google has made it available 58 00:05:11,220 --> 00:05:13,120 is a good idea in our ViewModel. 59 00:05:13,620 --> 00:05:15,420 One advantage it provides 60 00:05:15,420 --> 00:05:18,620 is that the coroutines will automatically be cancelled 61 00:05:18,620 --> 00:05:20,420 if the ViewModel is destroyed. 62 00:05:21,220 --> 00:05:23,880 That's not something we really have to worry about in this app. 63 00:05:24,480 --> 00:05:28,880 We're accessing a local database, and we're not performing massive bulk updates. 64 00:05:29,880 --> 00:05:32,980 But if you're downloading data from the internet, for example, 65 00:05:32,980 --> 00:05:35,280 then it would be something you would want to deal with. 66 00:05:36,180 --> 00:05:39,180 Now that Google have added ViewModelScope, it's easy. 67 00:05:39,730 --> 00:05:43,530 ViewModelScope takes care of cancelling our coroutines for us. 68 00:05:44,430 --> 00:05:46,730 I'll come back to this point in the next video. 69 00:05:47,230 --> 00:05:49,830 I'll start that video by testing the change and 70 00:05:50,230 --> 00:05:53,230 then we'll discuss that dispatcher. I'll see you there.