WEBVTT 00:00.120 --> 00:06.960 If you remember, we've added Hill Dependency Injection framework to our application. 00:07.000 --> 00:11.080 We need to use it for making dependency injection. 00:11.280 --> 00:15.080 So here inside this package, create a new Kotlin class. 00:15.080 --> 00:18.080 Name it as detection app. 00:18.120 --> 00:25.880 This class extends from application and if you want to learn more about dependency injection, please 00:25.880 --> 00:30.560 go back to the Dependency Injection section in the course. 00:30.600 --> 00:37.760 We need to annotate it with hilt Android application and use the Oncreate function. 00:37.880 --> 00:45.360 Set the log I for example detection application or tag and Oncreate. 00:45.400 --> 00:47.120 This is just for logging. 00:47.440 --> 00:53.080 Okay, but we need to create this class in order to specify it in the manifest. 00:53.080 --> 00:54.760 So back to the manifest. 00:54.760 --> 01:03.380 And here we don't specify the main activity or sorry the the name here, the name tag in the application 01:03.380 --> 01:06.940 name tag and set the detection app. 01:06.980 --> 01:07.620 Always. 01:07.620 --> 01:14.700 When you use Health Dependency injection, you should create a class that extends from application and 01:14.740 --> 01:17.140 annotate it with hilt Android app. 01:17.180 --> 01:26.540 The third step is to add the name attribute inside the application and specify this class. 01:26.540 --> 01:34.700 So after creating this class and specify it in the Android manifest, we need to make sure inside the 01:34.940 --> 01:39.780 ViewModel we use the hilt ViewModel annotation. 01:39.780 --> 01:44.420 So here the hilt ViewModel is set it used. 01:44.460 --> 01:49.820 The third thing we need to use for hilt is the main activity. 01:49.820 --> 01:57.580 So the detection app, the first part, the second part, the ViewModel, and the third part is the 01:57.580 --> 01:59.260 main activity. 01:59.420 --> 02:01.730 So inside this main activity. 02:01.730 --> 02:06.290 Annotate it with Android entry point annotation. 02:06.410 --> 02:12.490 So here we should specify it because it contains the Composables and the UI screen. 02:12.490 --> 02:15.650 And we are using Android with hilt. 02:15.690 --> 02:27.570 Now let me specify private val detection view model by view models and specify the detection view model. 02:27.730 --> 02:34.810 This line declares a ViewModel property using Kotlin's property delegation. 02:34.810 --> 02:40.810 So private detection ViewModel by Viewmodels. 02:40.850 --> 02:42.530 The detection ViewModel. 02:42.650 --> 02:51.250 The detection ViewModel is the name of the ViewModel property by is the Kotlin delegation keyword delegates 02:51.250 --> 03:03.030 property access to the delegate object, and the view models that delegate that creates or manages the 03:03.030 --> 03:04.750 ViewModel instance. 03:05.030 --> 03:06.750 This is very important. 03:06.750 --> 03:08.190 So this. 03:08.230 --> 03:13.230 This is the delegate that creates or manage the ViewModel instance. 03:13.550 --> 03:20.630 The ViewModel is created only when the first access, not when the class is initialized and the lifecycle 03:20.630 --> 03:21.150 management. 03:21.150 --> 03:25.910 The ViewModel survives configuration changes screen rotations. 03:25.950 --> 03:31.070 The same instance is reused across the fragments lifecycle, and we. 03:31.350 --> 03:40.830 We can also save the configuration changes across our compositions and make sure the that this delegation 03:40.830 --> 03:43.270 pattern is recommended. 03:43.270 --> 03:47.270 Way to access Viewmodels in Android development. 03:47.270 --> 03:52.590 Providing clean syntax with proper lifecycle management. 03:52.710 --> 03:57.910 Then inside the Oncreate remove the set content. 03:57.910 --> 04:02.060 So here object detection theme and remove it. 04:02.060 --> 04:06.340 Also remove the greeting composable and the preview okay. 04:06.540 --> 04:10.460 And inside this set content camera executor. 04:10.500 --> 04:12.780 We can create this variable here. 04:12.780 --> 04:19.540 Or we can make it like um like a global function like this detection ViewModel. 04:19.540 --> 04:25.820 So here private late initialize var camera executor. 04:25.940 --> 04:30.620 It's of type executor service alt plus enter to import the class. 04:30.660 --> 04:36.700 The executor service is a Java interface for managing thread execution. 04:36.700 --> 04:39.740 And this is used for camera operations. 04:39.740 --> 04:48.260 But why we use the late initialize fragments and activities are created by the system, so you can't 04:48.260 --> 04:56.020 pass parameters to the constructor you want to initialize when the component is ready on Oncreate or 04:56.020 --> 05:03.360 on view created, or any other composable, but here not when the class is created. 05:03.360 --> 05:07.600 So inside the set content we need to use this camera executor. 05:07.720 --> 05:13.760 Equals to executors dot new single thread executor. 05:13.800 --> 05:15.760 Alt plus enter to import it. 05:15.760 --> 05:17.280 And here we go. 05:17.320 --> 05:21.240 We created one single thread. 05:21.240 --> 05:25.440 Processes all camera tasks sequentially. 05:25.600 --> 05:27.600 This is a one single thread. 05:27.600 --> 05:34.240 Processes all camera tasks sequentially and good for simple camera operations. 05:34.240 --> 05:41.680 If you have multiple threads for parallel execution and processing, you can use new fixed new fixed 05:41.720 --> 05:44.760 thread pool, good for heavy image processing. 05:44.760 --> 05:52.080 But since our application is very simple and just for detecting objects, we don't make any process, 05:52.080 --> 05:55.240 any image process, any complex tasks. 05:55.280 --> 05:58.520 We use new single thread executor. 05:58.520 --> 06:03.910 So this is a pattern, a good pattern, no need for null checks everywhere. 06:04.150 --> 06:11.070 Initialize it at the right time in the life cycle and camera operations don't block the UI thread. 06:11.110 --> 06:13.150 This is the most important thing. 06:13.310 --> 06:16.870 The camera operations don't block the UI thread. 06:17.030 --> 06:19.790 Proper cleanup prevents memory leak. 06:20.030 --> 06:28.510 This pattern is essential for camera operations in Android to ensure smooth performance and proper resource 06:28.510 --> 06:29.510 management. 06:29.510 --> 06:38.150 And since it's a thread, we need to ensure that when when we destroy this function, when we exit this 06:38.190 --> 06:45.550 Oncreate function, we need to shut down this executor for this purpose. 06:45.790 --> 06:53.030 Override Ondestroy function and set the camera executor dot shut down.