1 00:00:05,500 --> 00:00:06,500 Welcome back. 2 00:00:06,800 --> 00:00:10,300 Our second improvement is to prevent a task from being deleted 3 00:00:10,500 --> 00:00:12,000 while it's being edited. 4 00:00:12,700 --> 00:00:14,600 That's only possible in landscape. 5 00:00:14,960 --> 00:00:17,660 So run the app then rotate into landscape. 6 00:00:26,260 --> 00:00:29,510 There's nothing to prevent the user from editing a task 7 00:00:29,510 --> 00:00:32,710 then deleting the same task by clicking its button. 8 00:00:33,310 --> 00:00:37,210 We'll add two more tasks so we've got something consistent to look at. 9 00:00:37,760 --> 00:00:40,660 By now you'll probably have a different set of tasks to me, 10 00:00:40,960 --> 00:00:44,560 especially if you've been experimenting with the interface and I hope you have. 11 00:00:45,160 --> 00:00:48,360 I'll call the first new task "Edit me" 12 00:00:59,660 --> 00:01:01,660 and the second one "Delete me". 13 00:01:08,960 --> 00:01:12,520 The description and sort order can be blank for both tasks, 14 00:01:12,520 --> 00:01:14,520 but make sure of course that you hit Save. 15 00:01:15,070 --> 00:01:18,070 Okay. Edit the Edit me task 16 00:01:18,870 --> 00:01:22,870 still in landscape, then click the button to delete 17 00:01:22,870 --> 00:01:24,670 the Delete me task. 18 00:01:27,470 --> 00:01:29,270 Choose Delete from the dialog, 19 00:01:30,670 --> 00:01:32,070 and the task is deleted. 20 00:01:32,730 --> 00:01:34,230 That seems to work fine. 21 00:01:34,730 --> 00:01:37,390 To be sure, enter a description 22 00:01:47,590 --> 00:01:48,580 and hit Save. 23 00:01:50,780 --> 00:01:51,780 That worked fine. 24 00:01:52,330 --> 00:01:56,030 So there's no problem allowing the user to delete one task 25 00:01:56,030 --> 00:01:57,630 while editing another one. 26 00:01:58,330 --> 00:02:00,630 Edit the Edit me task again. 27 00:02:01,680 --> 00:02:03,280 Tap the Delete button 28 00:02:05,270 --> 00:02:08,370 to delete the Edit me task that we're editing 29 00:02:08,370 --> 00:02:09,870 then choose Delete again. 30 00:02:11,120 --> 00:02:13,120 Now the app's in a strange state. 31 00:02:13,370 --> 00:02:16,870 It's editing a task that no longer exists in the database, 32 00:02:17,470 --> 00:02:19,770 and that's probably not going to go too well. 33 00:02:20,270 --> 00:02:22,070 So click Save to check. 34 00:02:23,670 --> 00:02:27,370 Sure enough, we lose any edits that the user may have made. 35 00:02:28,030 --> 00:02:30,030 Data loss is unforgivable, 36 00:02:30,230 --> 00:02:32,730 so we really need to do something about that one. 37 00:02:33,730 --> 00:02:36,930 You may think that the user would be fully aware of what they've done. 38 00:02:37,230 --> 00:02:40,430 We did ask for confirmation of the delete after all. 39 00:02:41,090 --> 00:02:44,590 But there's a big difference between running our apps on an emulator 40 00:02:44,590 --> 00:02:48,790 on a computer monitor and using the apps on a real mobile device. 41 00:02:49,590 --> 00:02:51,850 Users can pass a phone back and forth 42 00:02:52,250 --> 00:02:55,150 and tap things by accident when they do. 43 00:02:55,850 --> 00:02:58,450 So bear that in mind when testing on an emulator. 44 00:02:58,450 --> 00:03:02,950 It's not a true reflection of what happens to a handheld device with a touch screen. 45 00:03:04,150 --> 00:03:07,510 Editing a task is triggered by MainActivityFragment, 46 00:03:08,060 --> 00:03:11,060 that's the same class that responds to the delete button. 47 00:03:11,560 --> 00:03:15,560 So you may think it's going to be easy to track which task is being edited. 48 00:03:16,360 --> 00:03:18,860 Unfortunately, it's not that easy. 49 00:03:19,760 --> 00:03:22,960 MainActivityFragment knows when an edit starts 50 00:03:22,960 --> 00:03:24,960 and can store the task ID somewhere, 51 00:03:25,760 --> 00:03:29,120 but it doesn't know when a task is no longer being edited. 52 00:03:30,120 --> 00:03:33,020 We need some way for AddEditFragment 53 00:03:33,020 --> 00:03:36,020 to communicate with MainActivityFragment. 54 00:03:37,220 --> 00:03:38,720 We're using a ViewModel 55 00:03:38,970 --> 00:03:41,870 and that's the most reliable way to implement fragment 56 00:03:41,870 --> 00:03:43,370 to fragment communication. 57 00:03:44,270 --> 00:03:48,530 In TaskTimerModel, we'll create a read-only attribute 58 00:03:48,530 --> 00:03:50,530 called edited task ID. 59 00:03:51,230 --> 00:03:53,430 I'll put it just before the init block. 60 00:04:24,030 --> 00:04:26,630 Making the set function as private 61 00:04:26,930 --> 00:04:30,030 prevents external code from modifying the attribute. 62 00:04:32,030 --> 00:04:35,330 I'm going to use a pair of functions to change the value. 63 00:04:35,990 --> 00:04:39,590 Getters and setters aren't as common in Kotlin as they are in java, 64 00:04:39,890 --> 00:04:42,090 but they still exist and they have their uses. 65 00:04:42,590 --> 00:04:46,490 I'll paste the function in below the SaveTasks function 66 00:04:46,490 --> 00:04:48,690 then explain why I've used them. 67 00:04:57,790 --> 00:05:00,290 StopEditing is straightforward. 68 00:05:00,290 --> 00:05:04,190 It just sets the edit task ID attribute to zero. 69 00:05:04,990 --> 00:05:09,590 StartEditing includes some code that will only be used in our debug build. 70 00:05:10,590 --> 00:05:13,490 We want to be sure that there isn't a task being edited 71 00:05:13,490 --> 00:05:15,590 when we StartEditing another one. 72 00:05:16,690 --> 00:05:20,190 If we forget to StopEditing a task when the user's finished editing it, 73 00:05:20,590 --> 00:05:22,890 then that's a bug in the logic of our code. 74 00:05:23,490 --> 00:05:26,990 We want to detect that and fix the code if it happens. 75 00:05:28,190 --> 00:05:30,990 Okay. Our AddEditFragment 76 00:05:30,990 --> 00:05:34,790 will tell the ViewModel when it started and stops editing a task. 77 00:05:35,190 --> 00:05:36,790 Let's make that change next. 78 00:06:03,150 --> 00:06:06,810 We only need to do that when editing not when adding a task. 79 00:06:07,910 --> 00:06:10,210 A user can't delete a new task 80 00:06:10,210 --> 00:06:12,710 because it doesn't exist in the RecyclerView, 81 00:06:13,010 --> 00:06:15,010 so there's no delete button to tap. 82 00:06:15,260 --> 00:06:18,360 We StopEditing in the OnDetach function. 83 00:06:29,020 --> 00:06:32,820 Now we can test that value in MainActivityFragment 84 00:06:33,220 --> 00:06:36,220 and display a toast message instead of deleting. 85 00:07:54,220 --> 00:07:57,820 Use the light bulb to extract the text on line 71 86 00:08:02,220 --> 00:08:06,520 and call the resource delete_edited_task. 87 00:08:14,120 --> 00:08:17,120 That's a change completed, and we can test it. 88 00:08:17,780 --> 00:08:20,780 Run the app, and edit the task in landscape. 89 00:08:39,679 --> 00:08:43,179 Then use its delete button to try to delete it. 90 00:08:45,480 --> 00:08:48,480 We get the toast message instead and that's much better. 91 00:08:48,980 --> 00:08:51,340 Make sure you test deleting other tasks 92 00:08:51,640 --> 00:08:53,640 to make sure we haven't broken anything. 93 00:09:06,940 --> 00:09:09,300 There's a very important point to consider here. 94 00:09:09,960 --> 00:09:11,960 Remember back in section 12, 95 00:09:11,960 --> 00:09:16,110 we talked about sharing the ViewModelInstance between the fragments. 96 00:09:16,110 --> 00:09:19,010 It's crucial that you pass the activity 97 00:09:19,010 --> 00:09:22,310 when getting your ViewModelInstances in the fragments. 98 00:09:22,670 --> 00:09:23,970 That's our code 99 00:09:25,770 --> 00:09:27,270 up on line 32. 100 00:09:28,070 --> 00:09:31,870 If each fragment is using its own instance of the ViewModel, 101 00:09:31,870 --> 00:09:34,070 then this communication won't work. 102 00:09:34,620 --> 00:09:38,620 It's important to use by ActivityViewModels here 103 00:09:38,620 --> 00:09:40,920 and in the AddEditFragment class. 104 00:09:41,720 --> 00:09:45,620 If you need to get two or more fragments to communicate with each other, 105 00:09:45,620 --> 00:09:48,980 then doing it via the view model is a great way to achieve that. 106 00:09:49,780 --> 00:09:51,180 You may want to turn this around. 107 00:09:51,580 --> 00:09:55,580 At the moment, we've disabled deleting if a task is being edited. 108 00:09:56,240 --> 00:10:00,040 You may prefer to close the editing pane if the task is deleted. 109 00:10:00,640 --> 00:10:02,840 In that case, AddEditFragment 110 00:10:02,840 --> 00:10:05,740 would observe a LiveData object in the ViewModel 111 00:10:06,040 --> 00:10:07,640 and quietly close itself 112 00:10:08,140 --> 00:10:10,340 if the task it's editing gets deleted. 113 00:10:11,340 --> 00:10:14,940 That may be more appropriate. When creating your apps, you decide how they're going to function. 114 00:10:17,420 --> 00:10:21,570 In the next video, we'll look at removing the delete button from the layout 115 00:10:21,570 --> 00:10:25,670 and we'll implement delete by swiping instead. I'll see you there.