WEBVTT 00:00.080 --> 00:00.840 Welcome back. 00:01.200 --> 00:04.720 Now let's create the view model here. 00:04.720 --> 00:10.760 Inside this package create another package named as view model. 00:10.760 --> 00:12.480 Inside the View Models package. 00:12.480 --> 00:15.760 Create a new Kotlin class. 00:15.800 --> 00:19.160 Name it as Firebase View model. 00:19.200 --> 00:30.760 Or you can join Firebase location directions and all the repositories and all the methods and functions 00:30.760 --> 00:35.400 and operations in one view model like this. 00:35.400 --> 00:37.960 Named as map View model. 00:38.000 --> 00:42.480 Okay, this is for simplicity and not being confused okay. 00:42.640 --> 00:46.920 So after the repository we need to create the view model. 00:46.920 --> 00:48.240 This view model. 00:48.240 --> 00:54.040 This class will be annotated with hilt view model. 00:54.040 --> 00:56.200 Did you remember this annotation. 00:56.200 --> 01:00.270 It's very common and we use it in the previous videos. 01:00.270 --> 01:08.750 Hilton ViewModel is an annotation you put on your ViewModel class to telehealth, a dependency injection 01:08.750 --> 01:13.710 library that this ViewModel needs to be created by. 01:13.830 --> 01:21.350 Hilt automatically provide its dependencies like repositories via constructor injection. 01:21.350 --> 01:28.910 Why we use it so there is no need to manually create ViewModel factory's dependencies are injected automatically. 01:29.110 --> 01:35.790 Works seamlessly seamlessly with Jetpack Compose and Hilt ViewModel function. 01:35.830 --> 01:42.270 Okay, so this is the idea behind the usage of hilt ViewModel annotation. 01:42.270 --> 01:44.230 It's an annotation to put your. 01:44.350 --> 01:51.630 You put it on your ViewModel class to tell health that this ViewModel needs to be created by hilt, 01:51.870 --> 01:57.670 automatically provide its dependencies like repositories via constructor injection. 01:57.710 --> 02:01.390 Okay, so this is the hilt ViewModel annotation. 02:01.390 --> 02:03.270 Let's continue with this class. 02:03.270 --> 02:10.510 And here we need to use another uh in another annotation called inject annotation okay. 02:10.750 --> 02:16.870 The constructor private val marker repository. 02:16.910 --> 02:22.790 It's of type marker repository okay Alt+ enter to import it. 02:22.790 --> 02:23.990 And here we go. 02:24.230 --> 02:30.470 So this hilt ViewModel will automatically provide its dependencies. 02:30.470 --> 02:35.550 And in this case it's a marker repository via constructor injection. 02:35.590 --> 02:41.230 The next step is to tell Android Studio that this map view model is a ViewModel. 02:41.270 --> 02:45.390 By extending from View model class. 02:45.430 --> 02:49.110 Okay, this inherits from the ViewModel class. 02:49.230 --> 02:59.700 Now we need to create the function and marker, Which we'll call the repository dot add marker function. 02:59.700 --> 03:11.380 So function add marker takes four parameters the marker name on success and on failure callbacks that 03:11.380 --> 03:17.780 let lung it's of type Google maps model.lat long string. 03:18.060 --> 03:25.500 Then we need another parameters which are the callbacks on success. 03:25.660 --> 03:34.340 It's a lambda expression that takes nothing and returns nothing on failure takes exception and return 03:34.380 --> 03:35.100 nothing. 03:35.220 --> 03:37.660 Okay, this is the add marker. 03:37.700 --> 03:41.900 Now we need to define the body of this function. 03:41.900 --> 03:45.940 Start with view model scoop dot launch. 03:45.980 --> 03:50.860 This launches a coroutine bound to the view models lifecycle. 03:51.100 --> 03:57.020 If the view model is cleared, the coroutine is automatically canceled. 03:57.020 --> 04:06.260 It keep or it keeps work off the main thread, so this will be done in the background thread. 04:06.300 --> 04:07.780 What happens here? 04:08.060 --> 04:14.340 Try to call repository dot, add marker and insert marker with the name. 04:14.340 --> 04:23.300 If it completes successfully, call Onsuccess callback to notify your UI if anything fails. 04:23.300 --> 04:24.140 No internet. 04:24.140 --> 04:33.060 For example, go and execute the catch block, catch the exception and call the Onfailure function with 04:33.060 --> 04:38.060 the error so your UI can show an error message. 04:38.060 --> 04:41.100 The control flow of the flow of control. 04:41.380 --> 04:49.220 In this case UI calls ViewModel dot add marker a ViewModel launches a coroutine. 04:49.300 --> 04:54.290 Calls the repository to add a marker in Firebase. 04:54.570 --> 04:57.770 Wait for completion if it's success. 04:57.970 --> 05:01.530 Go and execute Onsuccess function and callback. 05:01.570 --> 05:08.770 Show a toast message or update UI or make a alert dialog if failed. 05:08.970 --> 05:14.690 Go and execute the Onfailure callback function called with the error. 05:14.810 --> 05:19.130 This is a good way for separation of concerns. 05:19.170 --> 05:22.090 Lifecycle safety and flexibility. 05:22.290 --> 05:24.810 So ViewModel handles business logic. 05:24.810 --> 05:30.610 Repository handles data storage UI just reacts to success or failure. 05:30.890 --> 05:31.850 ViewModel. 05:31.890 --> 05:35.530 Safety for the ViewModel scope prevents memory leaks. 05:35.570 --> 05:41.050 You can easily swap marker repository implementations for testing. 05:41.210 --> 05:46.610 Also, you can unit test map a ViewModel by mocking the repository.