1 00:00:04,200 --> 00:00:05,200 Welcome back. 2 00:00:05,400 --> 00:00:09,200 We're going to let how users choose the date that the report will display, 3 00:00:09,560 --> 00:00:13,360 and we'll do that using the android DatePickerDialog class. 4 00:00:14,060 --> 00:00:17,060 That's going to show a dialog that will let the user pick a date. 5 00:00:17,560 --> 00:00:19,160 You'll probably guess that from the name. 6 00:00:20,060 --> 00:00:23,560 We've covered dialog quite extensively in earlier videos. 7 00:00:24,110 --> 00:00:27,610 There are a couple of oddities about the DatePickerDialogue. 8 00:00:27,910 --> 00:00:30,910 So although, I won't be explaining the code in detail, 9 00:00:31,410 --> 00:00:34,010 I will talk about a couple of things that aren't obvious. 10 00:00:35,510 --> 00:00:38,710 The first is, don't show a DatePickerDialogue. 11 00:00:39,370 --> 00:00:41,570 The recommended way to use one 12 00:00:41,570 --> 00:00:44,370 is to use a DialogFragment instead. 13 00:00:45,360 --> 00:00:47,860 Google recommend that in a guide at 14 00:00:47,860 --> 00:00:52,060 developer.android.com/guide/topics/ui 15 00:00:52,360 --> 00:00:55,360 /control/pickers.html. 16 00:00:56,560 --> 00:00:58,560 At the time I'm recording this, 17 00:00:58,560 --> 00:01:00,860 the guide is also a really good example 18 00:01:00,860 --> 00:01:03,960 of why you need to be thorough when reading documentation. 19 00:01:04,620 --> 00:01:06,420 Let's start at the top and see what I mean. 20 00:01:07,410 --> 00:01:11,010 The guide talks about the DatePicker and TimePicker dialog 21 00:01:11,010 --> 00:01:12,310 that android provides. 22 00:01:13,190 --> 00:01:14,990 The images are a bit out of date. 23 00:01:15,350 --> 00:01:18,650 We're going to get the snazzy new dialog when we run the app. 24 00:01:19,450 --> 00:01:20,950 Just below the images is 25 00:01:20,950 --> 00:01:24,610 Google's recommendation to use a DialogFragment 26 00:01:25,110 --> 00:01:26,910 to host the date or TimePicker. 27 00:01:27,570 --> 00:01:29,770 Our code will be easy to change. 28 00:01:29,770 --> 00:01:33,370 Just modify the show DatePickerDialog function 29 00:01:33,770 --> 00:01:35,770 so you can quickly experiment 30 00:01:35,770 --> 00:01:38,770 with using a DatePickerDialog directly if you want to. 31 00:01:40,270 --> 00:01:42,770 You'll get strange effects with the life cycle. 32 00:01:43,270 --> 00:01:46,470 The picker will be dismissed when you rotate the phone for example. 33 00:01:46,970 --> 00:01:50,970 That's what they mean when they say DialogFragment manages the 34 00:01:50,970 --> 00:01:52,570 dialog lifecycle for you. 35 00:01:53,270 --> 00:01:55,570 So we will use a DialogFragment. 36 00:01:56,170 --> 00:01:59,470 Now things get a bit interesting, and we have to be awake. 37 00:02:00,070 --> 00:02:04,170 The paragraph after that talks about using the support library. 38 00:02:04,570 --> 00:02:07,170 We've been recommending you do that all along. 39 00:02:08,039 --> 00:02:12,340 Google also, as a rule, recommend the support libraries. 40 00:02:13,590 --> 00:02:17,950 The note below that suggests that you use the platform version 41 00:02:17,950 --> 00:02:22,850 of DialogFragment, if your minimum SDK is 11 or higher. 42 00:02:23,250 --> 00:02:26,650 Whenever you come across notes like that in the documentation, 43 00:02:26,650 --> 00:02:27,850 ignore them. 44 00:02:28,250 --> 00:02:30,850 Yes, you can use the framework version 45 00:02:31,100 --> 00:02:35,400 but I suggest you don't. Use the support libraries whenever you can. 46 00:02:36,300 --> 00:02:40,700 As I said, this is a great example of why you need to read things carefully 47 00:02:41,060 --> 00:02:43,360 and follow the links in the documentation. 48 00:02:44,460 --> 00:02:47,460 The final link to DialogFragment in that note 49 00:02:47,660 --> 00:02:51,960 takes us to the reference for the platform version of DialogFragment. 50 00:02:52,510 --> 00:02:54,110 So let's have a quick look at it. 51 00:02:56,470 --> 00:02:59,270 Make sure you click the final link, not the one before. 52 00:02:59,270 --> 00:03:02,770 The first link goes to the support library DialogFragment. 53 00:03:03,370 --> 00:03:07,570 Okay. We're at the page containing the reference for DialogFragment. 54 00:03:08,070 --> 00:03:10,570 It was introduced in API 11, 55 00:03:10,570 --> 00:03:13,930 but notice the note just below the class hierarchy at the top. 56 00:03:14,730 --> 00:03:18,930 This class was deprecated in API level 28. 57 00:03:19,480 --> 00:03:23,480 So we've just seen a guide suggesting that we can use this class 58 00:03:23,480 --> 00:03:26,080 for android versions 11 and above 59 00:03:26,380 --> 00:03:29,040 and now we have reference documentation informing 60 00:03:29,040 --> 00:03:32,640 us that the class will be removed from android at some point in the future. 61 00:03:33,190 --> 00:03:35,690 API 28, android pie, 62 00:03:36,190 --> 00:03:38,390 was released in 2018. 63 00:03:39,090 --> 00:03:42,690 The class might not be available in android queue. 64 00:03:43,290 --> 00:03:44,890 It probably will be. 65 00:03:45,290 --> 00:03:48,590 Deprecated classes tend to stick around for a couple of versions. 66 00:03:49,140 --> 00:03:52,840 But if we go using it, at some point, our code is going to break. 67 00:03:53,340 --> 00:03:57,700 I won't do this. But if you check out the framework version of the fragment class, 68 00:03:58,060 --> 00:03:59,360 that's also deprecated. 69 00:03:59,960 --> 00:04:03,360 It won't be a surprise if the FrameworkActivity class 70 00:04:03,360 --> 00:04:05,360 is also deprecated at some point. 71 00:04:05,960 --> 00:04:08,960 You should be using the appcompat versions, 72 00:04:08,960 --> 00:04:13,160 support library versions rather than the framework versions. 73 00:04:14,150 --> 00:04:18,029 Okay. That was interesting, but it's not getting our code written for us, 74 00:04:18,029 --> 00:04:19,529 so back to android studio. 75 00:04:20,190 --> 00:04:22,690 You want a new Kotlin class 76 00:04:22,690 --> 00:04:24,990 that I'm going to call DatePickerFragment. 77 00:04:37,980 --> 00:04:40,980 Remember choose class from the kind. 78 00:04:43,580 --> 00:04:45,880 We need to subclass dialog fragment 79 00:04:46,430 --> 00:04:49,660 and be sure to choose the support library version to import 80 00:04:49,960 --> 00:04:50,960 if you get the choice. 81 00:04:51,610 --> 00:04:56,210 That's androidx.fragment.app.AppCompatDialogFragment, 82 00:04:56,810 --> 00:04:59,110 if you're using androidx as I am. 83 00:05:08,310 --> 00:05:11,610 We're also going to implement the DatePickerDialogues 84 00:05:11,610 --> 00:05:13,970 on DateSetListener interface, 85 00:05:14,470 --> 00:05:17,370 that's how we'll get the chosen date back to our activity. 86 00:05:27,370 --> 00:05:30,370 I'll add a log tag and some constants that we'll need 87 00:05:30,370 --> 00:05:32,670 when retrieving things like the dialog title. 88 00:05:46,370 --> 00:05:49,670 We're going to use this DatePicker for a couple of different purposes. 89 00:05:50,330 --> 00:05:53,130 We'll use it to allow the user to filter the data. 90 00:05:53,330 --> 00:05:56,530 We'll also use it to let them choose a date when deleting records. 91 00:05:57,520 --> 00:06:01,820 We saw how we can use a dialog ID to respond differently 92 00:06:01,820 --> 00:06:03,020 to different dialog. 93 00:06:03,680 --> 00:06:06,880 But the DatePickerDialog doesn't provide that facility. 94 00:06:07,480 --> 00:06:10,840 We don't get an ID passed back in the CallBack function. 95 00:06:11,340 --> 00:06:14,640 That's not a huge problem we can implement our own solution. 96 00:06:15,300 --> 00:06:18,000 To do that, we need to store the ID. 97 00:06:30,770 --> 00:06:33,970 We have to override the OnCreateDialog function 98 00:06:33,970 --> 00:06:35,470 to customize the DatePicker, 99 00:06:35,870 --> 00:06:37,470 then return an instance of it. 100 00:06:38,070 --> 00:06:41,670 This is all code that we've seen before. So I won't say too much about it. 101 00:06:42,370 --> 00:06:46,470 Remember to choose the java.util package for the date 102 00:06:46,470 --> 00:06:48,470 and Gregorian calendar objects. 103 00:06:49,270 --> 00:06:53,630 Android studio can generate the OnCreate dialog stub for us, 104 00:06:53,990 --> 00:06:57,990 then we'll set up the calendar and create our DatePickerDialogue. 105 00:08:24,670 --> 00:08:26,170 That's fairly straightforward. 106 00:08:26,670 --> 00:08:29,370 We're providing the ability to use a different title 107 00:08:29,670 --> 00:08:33,659 and can also initialize the DatePicker with a specific date, 108 00:08:33,659 --> 00:08:36,760 if needed. That's going to be useful 109 00:08:36,760 --> 00:08:41,260 because the user will probably expect their last chosen date to be remembered 110 00:08:41,659 --> 00:08:43,760 as they change the dates of their reports. 111 00:08:45,120 --> 00:08:48,420 Notice that given date is a nullable data type, 112 00:08:49,020 --> 00:08:51,790 there may not be a date provided in the arguments 113 00:08:51,790 --> 00:08:55,690 in which case get serializable will return null. 114 00:08:56,290 --> 00:08:59,950 We test for that before setting the calendar to given date. 115 00:09:00,720 --> 00:09:02,820 Recent versions of android studio 116 00:09:02,820 --> 00:09:06,020 havebecome a bit aggressive about flagging up possible 117 00:09:06,020 --> 00:09:07,620 null pointer exceptions. 118 00:09:08,320 --> 00:09:11,520 That's generally a good thing, but sometimes it's a bit annoying. 119 00:09:12,320 --> 00:09:15,980 You may get a warning about context possibly being null 120 00:09:16,340 --> 00:09:19,340 when passing it to the DatePickerDialogue constructor. 121 00:09:20,140 --> 00:09:22,140 Theoretically, it can be null 122 00:09:22,840 --> 00:09:24,640 but. What are we supposed to do if it is? 123 00:09:25,300 --> 00:09:27,600 The function has to return a dialog. 124 00:09:28,200 --> 00:09:31,600 The super function is annotated as at, not null. 125 00:09:32,100 --> 00:09:34,700 That means we can't return null ourselves. 126 00:09:35,300 --> 00:09:38,960 If get context returns null, we can't create the dialog. 127 00:09:39,460 --> 00:09:40,460 So what can we return? 128 00:09:41,450 --> 00:09:45,750 Now, if you want to be a bit paranoid, you could wrap the code, 129 00:09:46,000 --> 00:09:50,100 the code that creates the DatePickerDialog in a null check. 130 00:09:50,900 --> 00:09:55,260 You'd then have to throw an exception if get context does return null. 131 00:09:55,510 --> 00:09:58,810 If we pass null to the DatePickerDialogue constructor, 132 00:09:59,250 --> 00:10:01,350 we're going to get an exception anyway. 133 00:10:01,450 --> 00:10:03,450 So why bother raising our own. 134 00:10:04,350 --> 00:10:09,010 If the activity is null at this point, then there's nothing that can catch the exception. 135 00:10:09,510 --> 00:10:11,810 Our code is going to crash whatever we do. 136 00:10:12,360 --> 00:10:15,560 Remember that all this is just theoretical, 137 00:10:16,060 --> 00:10:16,960 in theory, 138 00:10:16,960 --> 00:10:20,460 GetContext or GetActivity if we'd use that instead, 139 00:10:20,760 --> 00:10:21,960 could return null. 140 00:10:22,620 --> 00:10:25,120 Our activity has just created the fragment. 141 00:10:25,720 --> 00:10:29,620 It would be a bizarre set of conditions that could result in the activity 142 00:10:29,620 --> 00:10:31,120 being null at this point, 143 00:10:31,720 --> 00:10:33,420 if it's even possible in practice. 144 00:10:34,620 --> 00:10:39,120 So if you've got a warning there, you can suppress the warning. 145 00:10:39,920 --> 00:10:42,280 Use the light bulb to choose the option, 146 00:10:47,080 --> 00:10:51,380 nullability mismatch based on java annotation options. 147 00:10:52,180 --> 00:10:54,180 Then choose the first one in the list 148 00:10:54,480 --> 00:10:56,840 to disable the warning for the entire class. 149 00:11:01,440 --> 00:11:05,800 Okay. Next, we need to implement the DatePickerCallback function. 150 00:11:06,780 --> 00:11:09,880 Android studio can generate that code for us as well 151 00:11:10,540 --> 00:11:13,140 after the OncReateDialog function. 152 00:11:55,500 --> 00:11:58,160 It's possible for the context to be null, 153 00:11:58,160 --> 00:12:01,040 which is why I've cast it to be a nullable 154 00:12:01,040 --> 00:12:02,640 OnDateSet listener 155 00:12:03,240 --> 00:12:06,840 and used a safe call when calling the OnDateSet function. 156 00:12:07,440 --> 00:12:10,100 The DatePickerDialog passes back the date 157 00:12:10,100 --> 00:12:14,100 as three separate values when it calls OnDateSet. 158 00:12:14,900 --> 00:12:17,400 It also passes in a reference to the view. 159 00:12:18,060 --> 00:12:21,860 We can take advantage of that and attach the ID to the view, 160 00:12:22,360 --> 00:12:26,260 that lets the caller check the ID in its OnDateSet 161 00:12:26,260 --> 00:12:29,260 and take a different action for different date pickers, 162 00:12:29,810 --> 00:12:32,810 we'll see that shortly. Unfortunately, 163 00:12:32,810 --> 00:12:34,810 we've also got an error on that line. 164 00:12:35,170 --> 00:12:38,830 Android studio is complaining because the view argument 165 00:12:38,830 --> 00:12:41,130 could be null. Once again, 166 00:12:41,380 --> 00:12:45,380 I'm going to delete the nullable type marker from the function signature. 167 00:12:48,980 --> 00:12:52,420 In case you're thinking that I'm just doing this with wild abandon 168 00:12:52,420 --> 00:12:56,080 and no thought of the consequences, I have checked the source code 169 00:12:56,080 --> 00:12:58,580 for the DatePickerDialogue class. 170 00:12:59,460 --> 00:13:02,260 You can check it yourself if you want to be really sure. 171 00:13:03,060 --> 00:13:07,660 Look for the OnClick method and notice that the year, month and day arguments 172 00:13:07,860 --> 00:13:11,460 that we get are all fields of that DatePicker object, 173 00:13:11,460 --> 00:13:12,760 the view parameter. 174 00:13:13,260 --> 00:13:17,860 If the view was null, the DatePickerDialog code would have already crashed 175 00:13:17,860 --> 00:13:20,360 when attempting to access those fields. 176 00:13:20,720 --> 00:13:25,080 We'll see that dialog ID value being retrieved from the views tag 177 00:13:25,080 --> 00:13:26,280 in the next video. 178 00:13:27,160 --> 00:13:29,760 Okay. The only other thing you may want to do 179 00:13:29,760 --> 00:13:33,890 is to make sure that the activity does implement the required interface. 180 00:13:34,490 --> 00:13:36,490 We've seen this a few times now. 181 00:13:36,850 --> 00:13:39,150 I'll do it in the OnAttach function, 182 00:13:39,150 --> 00:13:42,150 which I'll generate before OnDateSet. 183 00:13:51,150 --> 00:13:52,350 Be careful there. 184 00:13:53,010 --> 00:13:57,310 There's a deprecated OnAttach function that has an activity argument. 185 00:13:57,810 --> 00:14:00,170 We want the one that takes a context. 186 00:14:20,370 --> 00:14:22,930 That's our DatePicker fragment finished for now. 187 00:14:23,480 --> 00:14:25,380 We're going to have to make a change to it 188 00:14:25,380 --> 00:14:28,980 because there's a bug in earlier versions of the DatePickerDialog. 189 00:14:29,780 --> 00:14:32,080 The bug was fixed in lollipop, I think. 190 00:14:32,680 --> 00:14:35,180 But it's certainly present in Jelly Bean and KitKat, 191 00:14:35,180 --> 00:14:37,540 and we're targeting API 17. 192 00:14:38,420 --> 00:14:40,920 I'll come back to that once we've seen the bug. 193 00:14:41,820 --> 00:14:46,120 In the next video, we'll use this fragment in our durations report, 194 00:14:46,370 --> 00:14:47,670 and we'll do some testing. 195 00:14:48,270 --> 00:14:49,870 I'm looking forward to it. See you there. 196 00:14:51,770 --> 00:14:55,170 Actually just before we do go, I noticed a typo. 197 00:14:56,470 --> 00:15:00,830 Our DatePickerFragment, down here, has a lowercase D. 198 00:15:01,380 --> 00:15:03,980 It's a class. It should have an uppercase D. 199 00:15:04,740 --> 00:15:08,400 Select the name, get a refactor, 200 00:15:09,760 --> 00:15:12,760 rename and just change that 201 00:15:14,260 --> 00:15:15,260 to a capital D. 202 00:15:16,250 --> 00:15:19,250 That's much better. Now, I'll see you in the next video.