1 00:00:05,150 --> 00:00:06,450 And welcome back, everyone. 2 00:00:07,000 --> 00:00:10,700 We've just seen our task vanished from the RecyclerView when we swipe it. 3 00:00:11,100 --> 00:00:12,500 That's normal behavior. 4 00:00:13,200 --> 00:00:17,840 What we have to do is make it appear again if the user cancels the deletion. 5 00:00:18,820 --> 00:00:19,810 It's easy to do. 6 00:00:20,360 --> 00:00:23,060 We need to get the position of the item that was swiped 7 00:00:23,360 --> 00:00:25,760 then tell the RecyclerView to put it back. 8 00:00:26,950 --> 00:00:29,850 We do that by calling the adapter's 9 00:00:29,850 --> 00:00:31,650 notifyItemChanged function 10 00:00:32,009 --> 00:00:35,010 and passing in the position of the item that was swiped. 11 00:00:35,370 --> 00:00:37,370 We'll do that in the dialogue's 12 00:00:37,370 --> 00:00:40,030 onNegativeDialogResult callback. 13 00:00:41,020 --> 00:00:44,020 Unfortunately, we decided not to implement that. 14 00:00:44,520 --> 00:00:47,520 So we'll have to make a couple of changes to AppDialog. 15 00:00:48,770 --> 00:00:52,270 Let's have a look in there at our dialog events interface 16 00:00:52,270 --> 00:00:53,660 at the start of the class. 17 00:00:59,160 --> 00:01:02,060 Now we've seen that interfaces are contracts, 18 00:01:02,860 --> 00:01:06,060 and you shouldn't change an interface once you've published it. 19 00:01:07,060 --> 00:01:10,060 If we add an OnNegativeDialogResult function 20 00:01:10,060 --> 00:01:12,060 to the DialogEvents interface, 21 00:01:12,060 --> 00:01:14,060 we'll break our existing classes. 22 00:01:15,420 --> 00:01:18,020 Fortunately, the android JVM 23 00:01:18,020 --> 00:01:20,720 now supports some Java 8 features. 24 00:01:21,220 --> 00:01:25,120 Not all of them, but it does support default implementations 25 00:01:25,120 --> 00:01:26,110 in interfaces. 26 00:01:26,990 --> 00:01:28,590 I'll create the problem, 27 00:01:28,590 --> 00:01:32,190 then we'll see how a default implementation can solve it. 28 00:01:33,180 --> 00:01:37,640 Start by uncommenting the two functions we decided not to implement. 29 00:01:43,140 --> 00:01:46,020 Anything that declares it implements this interface 30 00:01:46,020 --> 00:01:49,420 now has to implement those two additional functions. 31 00:01:50,410 --> 00:01:51,710 Rebuild the project, 32 00:01:55,210 --> 00:01:57,210 and see how much havoc we've caused. 33 00:02:00,210 --> 00:02:03,710 The build fails, and we've broken three classes. 34 00:02:04,610 --> 00:02:07,910 You can expand the messages in the build output pane 35 00:02:07,910 --> 00:02:10,210 to see that they all have the same error. 36 00:02:10,870 --> 00:02:14,570 We're not implementing the OnNegativeDialogResult function. 37 00:02:15,370 --> 00:02:16,370 That's not good. 38 00:02:17,030 --> 00:02:20,330 We don't really want to go changing unrelated classes 39 00:02:20,330 --> 00:02:23,330 just to make a change to the way we delete tasks. 40 00:02:24,630 --> 00:02:27,630 This is where a default implementation can save the day. 41 00:02:28,330 --> 00:02:32,330 If we provide a default implementation for the functions in an interface, 42 00:02:32,330 --> 00:02:34,830 java will use that implementation 43 00:02:34,830 --> 00:02:38,430 and not insist that our classes override the functions. 44 00:02:39,330 --> 00:02:41,690 Our default implementations won't do anything, 45 00:02:42,090 --> 00:02:45,790 we'll put an empty code block after the interface methods. 46 00:03:00,490 --> 00:03:03,990 Rebuild the project again, and we no longer get the errors. 47 00:03:09,980 --> 00:03:12,340 Our interface is now easier to use. 48 00:03:12,840 --> 00:03:16,240 Classes can override only those functions that they need, 49 00:03:16,240 --> 00:03:19,740 and don't have to provide a dummy implementation of the others. 50 00:03:20,620 --> 00:03:25,120 Our original code for AppDialog was written before Java 8 became available 51 00:03:25,120 --> 00:03:28,820 in the android JVM. We've now improved it, 52 00:03:28,820 --> 00:03:33,080 making it easy to use while still providing the ability to respond 53 00:03:33,080 --> 00:03:36,380 to any of the three ways the user may close the dialog. 54 00:03:37,480 --> 00:03:40,470 Android studio versions 3.whatever 55 00:03:40,470 --> 00:03:44,070 now support some of the new features added in Java 8. 56 00:03:44,730 --> 00:03:48,030 Default method implementations in interfaces is supported 57 00:03:48,390 --> 00:03:51,490 and that allows us to make our AppDialog class 58 00:03:51,490 --> 00:03:52,850 a bit easier to use. 59 00:03:54,210 --> 00:03:56,010 Before we finish with this class, 60 00:03:56,010 --> 00:04:00,010 we should uncomment the call to the listener's NegativeResult function 61 00:04:00,410 --> 00:04:02,710 and support the dialog being cancelled. 62 00:04:09,510 --> 00:04:13,310 That's down near the end of the class, near the CreateDialog function. 63 00:04:17,709 --> 00:04:20,110 I'll uncomment the OnCancel function. 64 00:04:22,410 --> 00:04:23,660 We weren't using it, 65 00:04:23,660 --> 00:04:27,160 but now we're notifying our listener if the dialog gets cancelled. 66 00:04:36,460 --> 00:04:39,960 The import you want is android.content 67 00:04:39,960 --> 00:04:42,460 .dialog interface if you're prompted. 68 00:04:42,820 --> 00:04:46,020 We saw that OnCancel function in an earlier video 69 00:04:46,380 --> 00:04:49,880 when we discussed making all three functions part of the interface. 70 00:04:50,540 --> 00:04:53,840 Now with default implementations in java 8, 71 00:04:53,840 --> 00:04:55,640 we've got the best of both worlds. 72 00:04:56,240 --> 00:05:00,340 Our interface can support positive and negative results and cancel 73 00:05:00,740 --> 00:05:04,140 without forcing classes to implement all three functions. 74 00:05:04,640 --> 00:05:07,640 We've got a strong warning on line 116. 75 00:05:08,440 --> 00:05:12,440 I mentioned this a few videos ago when we talked about RequireContext. 76 00:05:12,800 --> 00:05:13,700 This is similar. 77 00:05:14,690 --> 00:05:17,490 We've had to use arguments bang bang 78 00:05:17,850 --> 00:05:21,350 because the compiler can't be sure that our arguments aren't null. 79 00:05:22,010 --> 00:05:26,010 We know it's not null. We check that in the OnCreateDialog function, 80 00:05:26,370 --> 00:05:27,970 but the compiler can't be sure. 81 00:05:28,960 --> 00:05:33,360 Using the bang bang operator is how we tell the compiler that we know what we're doing. 82 00:05:34,350 --> 00:05:36,550 Now there's a slightly neater way. 83 00:05:36,910 --> 00:05:40,110 Click on arguments on line 116, 84 00:05:40,510 --> 00:05:43,410 and accept the suggestion to replace with 85 00:05:43,410 --> 00:05:45,400 require arguments instead. 86 00:05:49,280 --> 00:05:53,080 I won't go into it all again, refer to the video entitled 87 00:05:53,080 --> 00:05:56,440 "Another Breaking Change" earlier in this section 88 00:05:56,440 --> 00:05:58,940 if you want to remind yourself what this is all about. 89 00:05:59,820 --> 00:06:03,720 In the next video we'll see how to use the NegativeDialogResult 90 00:06:03,720 --> 00:06:06,720 to make the task appear in the RecyclerView again. 91 00:06:06,720 --> 00:06:07,820 I'll see you over there.