android - LiveData 和 LifecycleObserver 有什么区别

Question

我已阅读有关 Life Cycle 的文档和 Live Data在android官方文档中。我知道该类实现了 LifeCycleObserver 并使位置监听器自动关闭或打开。我也知道实时数据可以自动使其处于 Activity 状态或不活动状态。我尝试使用这两种方式来实现 Location Observer。它有效，并且在更新位置时显示 Toast 2 次。

我的问题是，如果我真的想实现数据库连接、GPS 定位、下载图像、运行后台服务等功能，这两种方式有什么区别。我可以只使用 LiveData 类吗？因为我只需要实现 active 和 inactive 功能。

LocationLiveData.java

public class LocationLiveData extends LiveData<Location> {
    private LocationManager locationManager;
    private Context context;

    public LocationLiveData(Context context) {
        this.context = context;
        locationManager = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);
    }

    private LocationListener locationListener = new LocationListener() {
        @Override
        public void onLocationChanged(Location location) {
            setValue(location);
        }

        @Override
        public void onStatusChanged(String provider, int status, Bundle extras) {

        }

        @Override
        public void onProviderEnabled(String provider) {

        }

        @Override
        public void onProviderDisabled(String provider) {

        }
    };

    @Override
    protected void onActive() {
        super.onActive();
        if (ActivityCompat.checkSelfPermission(context, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(context, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            // TODO: Consider calling
            //    ActivityCompat#requestPermissions
            // here to request the missing permissions, and then overriding
            //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
            //                                          int[] grantResults)
            // to handle the case where the user grants the permission. See the documentation
            // for ActivityCompat#requestPermissions for more details.
            return;
        }
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);
    }

    @Override
    protected void onInactive() {
        super.onInactive();
        locationManager.removeUpdates(locationListener);
    }
}

MyLocationListener.java

public class MyLocationListener implements LifecycleObserver {
    private LocationManager locationManager;
    private Context context;
    private LocationListener locationListener;


    public MyLocationListener(LifecycleActivity lifecycleActivity, LocationListener callback) {
        // ...
        this.context = lifecycleActivity;
        locationManager = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);
        locationListener = callback;

    }

    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    public void onResume() {
        if (ActivityCompat.checkSelfPermission(context, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(context, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            // TODO: Consider calling
            //    ActivityCompat#requestPermissions
            // here to request the missing permissions, and then overriding
            //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
            //                                          int[] grantResults)
            // to handle the case where the user grants the permission. See the documentation
            // for ActivityCompat#requestPermissions for more details.
            return;
        }
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    public void onPause() {
        locationManager.removeUpdates(locationListener);
    }
}

ComponentActivity.java

public class ComponentActivity extends LifecycleActivity {
    public static final int REQUEST_CODE = 200;
    private MyLocationListener myLocationListener;
    public static class MyLiveData extends ViewModel {
        private LocationLiveData locationLiveData;

        public void init(Context context) {
            locationLiveData = new LocationLiveData(context);
        }

        public LocationLiveData getLocationLiveData() {
            return locationLiveData;
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_component);
//        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
//        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
        ActivityCompat.requestPermissions(this,
                new String[]{Manifest.permission.ACCESS_COARSE_LOCATION, Manifest.permission.ACCESS_FINE_LOCATION},
                REQUEST_CODE);
        // MY_PERMISSIONS_REQUEST_READ_CONTACTS is an
        // app-defined int constant. The callback method gets the
        // result of the request.

        //use the live data observer
        MyLiveData myLiveData = ViewModelProviders.of(this).get(MyLiveData.class);
        myLiveData.init(this);
        myLiveData.getLocationLiveData().observe(this, new Observer<Location>() {
            @Override
            public void onChanged(@Nullable Location s) {
                Toast.makeText(ComponentActivity.this, String.format("Lat : %.2f, Lon : %.2f", s.getLongitude(), s.getLatitude()), Toast.LENGTH_SHORT).show();
            }
        });
        //use the life cycle observer
        getLifecycle().addObserver(new MyLocationListener(this, new LocationListener() {
            @Override
            public void onLocationChanged(Location s) {
                Toast.makeText(ComponentActivity.this, String.format("Lat : %.2f, Lon : %.2f", s.getLongitude(), s.getLatitude()), Toast.LENGTH_SHORT).show();
            }

            @Override
            public void onStatusChanged(String provider, int status, Bundle extras) {

            }

            @Override
            public void onProviderEnabled(String provider) {

            }

            @Override
            public void onProviderDisabled(String provider) {

            }
        }));


    }

    @Override
    public void onRequestPermissionsResult(int requestCode,
                                           String permissions[], int[] grantResults) {
        switch (requestCode) {
            case 200: {
                // If request is cancelled, the result arrays are empty.
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {

                    // permission was granted, yay! Do the
                    // contacts-related task you need to do.

                } else {

                    // permission denied, boo! Disable the
                    // functionality that depends on this permission.
                }
                return;
            }

            // other 'case' lines to check for other
            // permissions this app might request
        }
    }

}

Answer 1

它们是完全不同的东西，担当着两个不同的角色。简而言之，

• LifeCycle以有效且简单的方式解决 Android 生命周期问题。它有两个主要部分。 LifecycleOwner公开其状态变化，并且 LifecycleObserver聆听这些变化以做出适当的步骤。
• LiveData另一方面，利用响应式(Reactive)编程帮助我们轻松地操作数据。它与 Stream 有一些相似之处在Java 8和 Observer (或 Flowable )在 RxJava .但是，LiveData 的一个优势是它具有特定于 Android 的生命周期感知能力。因此，它与 LifeCycle 组件紧密协作。