Lonelywood/Android-Samples-IsolateComponents

Samples in this repository may help you explain how isolate components which must start another intent and wait for result.

How to isolate component from activity when it needs start the intent for result?

Stackoverflow question: Here

Problem:

I need to create a component whose task will be to provide photo file from camera intent. Until now, i did those things in activity by starting another activity for result and waiting for it. But now I want to use that component from business logic layer where is no access to UI layer (activities). How to create a component that meets these requirements?

Solution:

1. In custom Application class make available context through create static getter for instance App class.

    public class App extends Application {
        private static App instance;
   
        @Override
        public void onCreate() {
            instance = this;
        }
   
        public static App getInstance(){
            return instance;
        }
    }
   

   If you are using dependency injection I strongly recommend provide App class by it.

2. Create an interface for component that describes what component can do. Here we have function takePhoto() and two another functions for add and remove listener.

    public interface PhotoTakerComponent {
        void takePhoto();
        void addListener(PhotoTakerListener listener);
        void removeListener(PhotoTakerListener listener);
    }
   

3. Implementation of PhotoTakerComponent will communicate with our biusness layer class by listener - PhotoTakerListener.

    public interface PhotoTakerListener {
        void onPhotoTaken(Boolean success, String path);
    }
   

4. Now create PhotoTakerActivity. This activity will be component internal class without layout. We will start it only for start correct intent and wait for reslut at onActivityResult method. After all this will be instantly finished. User will never see this activity because we will not inflate any layout.

    public class PhotoTakerActivity extends AppCompatActivity {
   
        ...
   
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            
            ...
   
            Uri uri = Uri.parse(mFileName);
   
            Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
            intent.putExtra(MediaStore.EXTRA_OUTPUT, **uri**);
   
            if (intent.resolveActivity(getPackageManager()) != null) {
                startActivityForResult(intent, RequestImageCapture);
            }
        }
   
        @Override
        protected void onActivityResult(int requestCode, int resultCode, Intent data) {
            super.onActivityResult(requestCode, resultCode, data);
   
            if (requestCode == RequestImageCapture) {
                if (resultCode == RESULT_CANCELED){
                    for (PhotoTakerListener listener: listeners) {
                        listener.onPhotoTaken(false, null);
                    }
                } else if (resultCode == RESULT_OK){
                    for (PhotoTakerListener listener: listeners){
                        listener.onPhotoTaken(true, mFileName);
                    }
                }
            }
   
            finish();
        }
    }
   

5. In the last step we must create implementation of PhotoTakerComponent interface where in takePhoto() method we starting internal PhotoTakerActivity.

    public class DefaultPhotoTakerComponent implements PhotoTakerComponent {
        private Context mApplicationContext;
   
        public DefaultPhotoTakerComponent() {
            mApplicationContext = App.getInstance().getApplicationContext();
        }
   
        @Override
        public void takePhoto() {
            if (mApplicationContext.getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA)) {
                try {
                    
                    ...
   
                    Intent intent = new Intent(mApplicationContext, PhotoTakerActivity.class);
                    intent.putExtra(PhotoTakerActivity.ExtraFileName, Uri.fromFile(image).toString());
                    intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
   
                    mApplicationContext.startActivity(intent);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
   
        public void addListener(PhotoTakerListener listener){
            PhotoTakerActivity.addListener(listener);
        }
   
        public void removeListener(PhotoTakerListener listener){
            PhotoTakerActivity.removeListener(listener);
        }
    }
   

Sample application is available on Github:

For Java Android: Here and for C# Xamarin.Android: Here