1 00:00:04,800 --> 00:00:07,300 Welcome back. In this video, 2 00:00:07,300 --> 00:00:10,600 we're going to observe the changes to the device configuration 3 00:00:10,900 --> 00:00:14,800 to allow our app to respond when the locale changes. 4 00:00:15,460 --> 00:00:17,260 When something like this happens, 5 00:00:17,260 --> 00:00:21,160 the system will broadcast a message to any broadcast receivers 6 00:00:21,160 --> 00:00:23,160 that have registered to be notified. 7 00:00:23,960 --> 00:00:25,960 Setting up a BroadcastReceiver 8 00:00:26,260 --> 00:00:29,260 follows the same pattern as setting up a ContentObserver. 9 00:00:30,250 --> 00:00:34,650 We have to create an object that will respond to the messages then register it. 10 00:00:35,310 --> 00:00:37,910 When we no longer need it, we unregister it. 11 00:00:39,110 --> 00:00:43,310 One difference is how we specify which broadcasts we're interested in. 12 00:00:44,190 --> 00:00:46,290 When using a ContentObserver, 13 00:00:46,290 --> 00:00:48,790 we tell it which URI to observe. 14 00:00:49,190 --> 00:00:53,390 With a BroadcastReceiver, we use an IntentFilter instead. 15 00:00:53,690 --> 00:00:54,990 Let's see some code. 16 00:00:57,490 --> 00:01:00,790 I'll start by creating a BroadcastReceiver object 17 00:01:00,790 --> 00:01:02,690 in our DurationsViewModel. 18 00:01:43,350 --> 00:01:47,850 We've got an error because we need to implement the OnReceive function. 19 00:01:48,950 --> 00:01:52,950 I'll use control I to get android studio to generate the stub. 20 00:01:56,550 --> 00:01:59,320 The OnReceive function is an abstract function 21 00:01:59,320 --> 00:02:01,120 in the BroadcastReceiver class, 22 00:02:01,120 --> 00:02:02,420 which is also abstract. 23 00:02:03,120 --> 00:02:06,420 That means we have to provide the implementation ourselves. 24 00:02:07,280 --> 00:02:11,280 An abstract class is similar to an interface in many ways. 25 00:02:11,780 --> 00:02:13,580 There are some important differences. 26 00:02:13,880 --> 00:02:16,680 And if you don't already know about abstract classes, 27 00:02:16,680 --> 00:02:20,580 it's worth Googling for something like "JavaAbstract class 28 00:02:20,580 --> 00:02:23,180 versus interface" to learn more about them. 29 00:02:23,980 --> 00:02:27,280 An abstract class can provide some implementation itself, 30 00:02:27,640 --> 00:02:29,140 which an interface couldn't 31 00:02:29,440 --> 00:02:32,040 but that distinction has faded a bit recently 32 00:02:32,700 --> 00:02:36,000 because interfaces can now provide some implementation 33 00:02:36,300 --> 00:02:37,900 in later java versions. 34 00:02:38,200 --> 00:02:40,400 All right. What do we want to do 35 00:02:40,400 --> 00:02:43,900 when we receive a notification that the locale has changed. 36 00:02:44,800 --> 00:02:46,700 We've already discussed that in fact. 37 00:02:47,100 --> 00:02:50,400 We need to create a new Gregorian calendar instance, 38 00:02:50,760 --> 00:02:54,360 so that the calendar is using the settings for the new locale. 39 00:02:55,020 --> 00:02:57,520 The user may have changed the calendar's date 40 00:02:57,920 --> 00:03:00,520 and will probably expect to still see that date. 41 00:03:01,070 --> 00:03:05,060 That means we should store the date then set a new calendar instance 42 00:03:05,060 --> 00:03:05,960 to use it. 43 00:03:25,260 --> 00:03:28,260 There's no way to change the locale of a calendar instance, 44 00:03:28,510 --> 00:03:30,210 which is why we create a new one. 45 00:03:30,810 --> 00:03:34,210 That means we have to declare our calendar as var 46 00:03:34,210 --> 00:03:35,710 rather than val. 47 00:03:40,710 --> 00:03:41,910 That's fixed the error. 48 00:03:42,570 --> 00:03:47,170 After creating a new calendar instance, we call the ApplyFilter function, 49 00:03:47,770 --> 00:03:51,540 that re-queries the database and make sure the report reflects 50 00:03:51,540 --> 00:03:53,040 what the user expects. 51 00:03:53,840 --> 00:03:55,340 There's something else we should do, 52 00:03:55,840 --> 00:03:59,830 and that's described in the docs string for the BroadcastReceivers 53 00:03:59,830 --> 00:04:01,330 OnReceive method. 54 00:04:01,730 --> 00:04:05,730 Control click on BroadcastReceiver on line 44 55 00:04:06,230 --> 00:04:07,630 to see the source code, 56 00:04:13,130 --> 00:04:15,330 that takes us to the class constructor 57 00:04:15,930 --> 00:04:19,529 and the docs string below that relates to the OnReceive method. 58 00:04:22,530 --> 00:04:26,090 This is java code remember which is why I'm saying method 59 00:04:26,090 --> 00:04:27,190 instead of function. 60 00:04:27,990 --> 00:04:29,990 It's worth reading the docs strings 61 00:04:29,990 --> 00:04:32,290 or the google documentation if you prefer 62 00:04:32,790 --> 00:04:35,790 for any classes and methods that you use in your apps. 63 00:04:36,290 --> 00:04:40,590 You'll often find unexpected details that can save you getting into difficulties. 64 00:04:42,890 --> 00:04:45,090 I'm interested in the last paragraph here, 65 00:04:45,090 --> 00:04:47,290 just above the parameter descriptions. 66 00:04:47,650 --> 00:04:49,250 But I'm not going to read it just yet. 67 00:04:49,650 --> 00:04:53,900 It'll make a bit more sense once we've finished setting up the BroadcastReceiver. 68 00:04:54,400 --> 00:04:59,000 Back in our DurationsViewModel class, we need to register the receiver, 69 00:05:00,800 --> 00:05:03,400 that involves creating an IntentFilter 70 00:05:03,400 --> 00:05:05,400 for the messages we want to receive. 71 00:05:06,200 --> 00:05:08,500 I'll add the code in the init block. 72 00:05:24,800 --> 00:05:28,900 The IntentFilter tells android which broadcast messages 73 00:05:28,900 --> 00:05:30,000 we want to receive. 74 00:05:30,600 --> 00:05:33,400 Here, we're going to create a new calendar instance 75 00:05:33,400 --> 00:05:35,900 if the user changes the locale 76 00:05:35,900 --> 00:05:39,260 because that changes things like which day the week starts on. 77 00:05:40,060 --> 00:05:43,560 We also create a new calendar if they change time zones 78 00:05:44,000 --> 00:05:47,300 that's obviously something our calendar needs to know about. 79 00:05:48,600 --> 00:05:51,600 You can add as many IntentFilters as you need 80 00:05:51,960 --> 00:05:54,560 by calling the AddAction method 81 00:05:54,810 --> 00:05:56,810 and providing the action you're interested in. 82 00:05:57,810 --> 00:06:00,110 We finish by registering our server 83 00:06:00,360 --> 00:06:04,560 by calling the RegisterReceiver method of the application object. 84 00:06:05,760 --> 00:06:08,120 In the documentation that you google for, 85 00:06:08,120 --> 00:06:11,720 you'll find a discussion about the context of your receiver. 86 00:06:12,520 --> 00:06:14,920 If we were doing this in an activity, 87 00:06:14,920 --> 00:06:18,420 we'd call the activities RegisterReceiver method 88 00:06:19,220 --> 00:06:22,420 that would allow the activity to receive the broadcasts 89 00:06:22,420 --> 00:06:24,320 until the activity gets destroyed. 90 00:06:25,620 --> 00:06:28,720 We're using the application to register our receiver, 91 00:06:28,720 --> 00:06:32,120 which means it will remain registered as long as the app is running. 92 00:06:33,420 --> 00:06:36,520 Of course, we're going to do things properly 93 00:06:36,520 --> 00:06:40,520 and unregister the receiver when our ViewModel gets destroyed. 94 00:06:40,880 --> 00:06:43,380 We do that in the uncleared function. 95 00:07:06,880 --> 00:07:11,280 Before we test it, let's have another look at the code in our init block. 96 00:07:13,680 --> 00:07:17,280 We've created an intent filter that specifies 97 00:07:17,830 --> 00:07:20,530 action time zone changed and 98 00:07:20,830 --> 00:07:22,430 action locale changed. 99 00:07:23,230 --> 00:07:27,630 That means we should only receive messages when those events are broadcast. 100 00:07:28,180 --> 00:07:31,480 I'm going to add some more code to the OnReceive function, 101 00:07:31,480 --> 00:07:32,980 then we'll have a look why. 102 00:08:03,780 --> 00:08:05,780 Okay. Why have I done that. 103 00:08:06,280 --> 00:08:10,080 If we're only going to get called when one of those actions is broadcast, 104 00:08:10,480 --> 00:08:11,680 why bother checking? 105 00:08:12,930 --> 00:08:16,530 The reason's described in the last paragraph of that doc string. 106 00:08:17,190 --> 00:08:18,690 Let's have another look at it. 107 00:08:19,190 --> 00:08:23,390 Ctrl click on BroadcastReceiver to go back to the source for the class. 108 00:08:24,290 --> 00:08:28,790 It says that the Intent filters are not guaranteed to be exclusive, 109 00:08:29,490 --> 00:08:33,789 they're hints to the android framework but we may get other messages, 110 00:08:34,289 --> 00:08:38,490 that's why we should check that the actions are only the ones that we are interested in. 111 00:08:39,150 --> 00:08:41,350 Now in this particular app, 112 00:08:41,549 --> 00:08:44,250 it's not crucial if we create a new calendar 113 00:08:44,250 --> 00:08:45,850 when some other event occurs, 114 00:08:46,510 --> 00:08:49,510 it's inefficient but it won't cause serious problems. 115 00:08:50,310 --> 00:08:53,010 But there may be situations where it is important. 116 00:08:53,410 --> 00:08:56,310 So make sure you always check the intent action 117 00:08:56,310 --> 00:08:58,310 that causes your receiver to be called. 118 00:08:59,190 --> 00:09:01,090 All right. That code's finished. 119 00:09:01,690 --> 00:09:06,090 In the next video, we'll test the app to make sure that we've fixed the bug. 120 00:09:06,490 --> 00:09:07,390 See you there.