Annyce Davis

Davis Technology Consulting

Android: Overdraw, What is it and Why Should You Care?

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I recently read this blog post,  Android Performance Case Study by Romain Guy, on profiling an application that he used regularly to determine why there were occasional hiccups.  I used one of the tools he recommended, Debug GPU Overdraw, to see how the PostTV Application was behaving. With one minor tweak I was able to reduce the overdraw by 1x.  So what does overdraw mean anyway?

Overdraw is when you draw pixels on top of each other potentially effecting the speed with which your application draws views on the screen.  Ideally you don’t want to have more than “2.5 times the number of pixels on screen per frame.”  And the different colors each represent how many times the pixel has been painted on the screen.

Taken directly from Romain’s post:


So by simply removing the background color that was assigned to my main layout, I was able to get a 1x overdraw instead of a 2x. Which is why most of the app is now a happy blue color!

 

Android: Custom Gson Deserialization

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So here’s the scenario you have a JSON Object that contains a list of objects. Each one of the objects in the primary JSON Object also contain a list of objects. So for demonstration purposes we will use a car with a list of seats and each seat has a list of buckles (Car -> Seats -> Buckles). Completely random example, yes I know.

So if you have the use case where you don’t want to deserialize any seats that don’t have buckles this is how you can do it using a Custom GSON Deserializer.

First, this is a sample JSON response which contains the information for each car:

[{
    "description": "A nice car",
    "name": "Toyota",
    "seats": [{
        "buckles": [],
        "type": "front"
    }, {
        "buckles": ["latch", "snap"],
        "type": "front"
    }]
}]

What you will notice is that there is one Seat object that has an empty list of Buckle objects. So in that case you don’t want Gson to include that seat in the final list of seat objects.  We will use two advanced features of Gson: Exclusion Strategies and Custom Deserializer. 

Since we want to handle the “seats” array on our own we will create an Annotation that can be used by Gson to ignore the field during normal processing.

Car Class (portion):

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD})
public @interface SkipThis {

}

@SkipThis
private List<SeatVO> seats;

Now we can proceed to exclude any field that has our custom SkipThis annotation by means of an ExclusionStrategy.

private static class SkipThisAnnotationExclusionStrategy
implements ExclusionStrategy {
    public boolean shouldSkipClass(Class clazz) {
        return clazz.getAnnotation(CarVO.SkipThis.class) != null;
    }
 
    public boolean shouldSkipField(FieldAttributes f) {
        return f.getAnnotation(CarVO.SkipThis.class) != null;
    }
}

Finally, we can proceed to create the custom deserializer that will check for the existence of items in the “buckles” array.

@Override
public CarVO deserialize(JsonElement json, Type arg1,
                         JsonDeserializationContext arg2) throws JsonParseException {
  JsonObject carsJSON = json.getAsJsonObject();
  JsonArray seatsJSON = carsJSON.getAsJsonArray("seats");
 
  Gson g = new Gson();
  CarVO carVO = g.fromJson(json, CarVO.class);
  List<SeatVO> res = new ArrayList<SeatVO>();
 
  for (JsonElement elem : seatsJSON) {
    JsonArray bucklesJSON = elem.getAsJsonObject().getAsJsonArray("buckles");
    if (!bucklesJSON.isJsonNull() && bucklesJSON.size() > 0) {
      res.add(g.fromJson(elem, SeatVO.class));
    }
  }
 
  carVO.setSeats(res);
 
  return carVO;
}

The complete code:

Android: Location Updates with the FusedLocationApi

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If you want to retrieve the user’s location in your Android application you can take advantage of Google’s FusedLocationApi. Essentially you establish a connection to the GoogleApiClient and then set up a LocationRequest.  It’s up to you to configure the rate at which you would like to receive updates.  Here is an example of using the API:

import android.app.Activity;
import android.content.Intent;
import android.location.Location;
import android.net.Uri;
import android.os.Bundle;

import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesUtil;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.location.LocationListener;
import com.google.android.gms.location.LocationRequest;
import com.google.android.gms.location.LocationServices;

import java.util.List;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class MainActivity extends Activity implements
                                           LocationListener,
                                           GoogleApiClient.ConnectionCallbacks,
                                           GoogleApiClient.OnConnectionFailedListener {

    private static final long ONE_MIN = 1000 * 60;
    private static final long TWO_MIN = ONE_MIN * 2;
    private static final long FIVE_MIN = ONE_MIN * 5;
    private static final long POLLING_FREQ = 1000 * 30;
    private static final long FASTEST_UPDATE_FREQ = 1000 * 5;
    private static final float MIN_ACCURACY = 25.0f;
    private static final float MIN_LAST_READ_ACCURACY = 500.0f;

    private LocationRequest mLocationRequest;
    private Location mBestReading;

    private GoogleApiClient mGoogleApiClient;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if (!servicesAvailable()) {
            finish();
        }

        setContentView(R.layout.activity_main);

        mLocationRequest = LocationRequest.create();
        mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
        mLocationRequest.setInterval(POLLING_FREQ);
        mLocationRequest.setFastestInterval(FASTEST_UPDATE_FREQ);

        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .addApi(LocationServices.API)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .build();
    }

    @Override
    protected void onResume() {
        super.onResume();

        if (mGoogleApiClient != null) {
            mGoogleApiClient.connect();
        }
    }

    @Override
    protected void onPause() {
        super.onPause();

        if (mGoogleApiClient != null && mGoogleApiClient.isConnected()) {
            mGoogleApiClient.disconnect();
        }
    }

    @Override
    public void onLocationChanged(Location location) {
        // Determine whether new location is better than current best
        // estimate
        if (null == mBestReading || location.getAccuracy() < mBestReading.getAccuracy()) {
            mBestReading = location;

            if (mBestReading.getAccuracy() < MIN_ACCURACY) {
                LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, this);
            }
        }
    }

    @Override
    public void onConnected(Bundle dataBundle) {
        // Get first reading. Get additional location updates if necessary
        if (servicesAvailable()) {
            // Get best last location measurement meeting criteria
            mBestReading = bestLastKnownLocation(MIN_LAST_READ_ACCURACY, FIVE_MIN);

            if (null == mBestReading
                    || mBestReading.getAccuracy() > MIN_LAST_READ_ACCURACY
                    || mBestReading.getTime() < System.currentTimeMillis() - TWO_MIN) {

                LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this);
                
                // Schedule a runnable to unregister location listeners
                Executors.newScheduledThreadPool(1).schedule(new Runnable() {

                    @Override
                    public void run() {
                        LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, MainActivity.this);
                    }

                }, ONE_MIN, TimeUnit.MILLISECONDS);
            }
        }
    }

    @Override
    public void onConnectionSuspended(int i) {
        
    }

    private Location bestLastKnownLocation(float minAccuracy, long minTime) {
        Location bestResult = null;
        float bestAccuracy = Float.MAX_VALUE;
        long bestTime = Long.MIN_VALUE;

        // Get the best most recent location currently available
        Location mCurrentLocation = LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient);

        if (mCurrentLocation != null) {
            float accuracy = mCurrentLocation.getAccuracy();
            long time = mCurrentLocation.getTime();

            if (accuracy < bestAccuracy) {
                bestResult = mCurrentLocation;
                bestAccuracy = accuracy;
                bestTime = time;
            }
        }

        // Return best reading or null
        if (bestAccuracy > minAccuracy || bestTime < minTime) {
            return null;
        }
        else {
            return bestResult;
        }
    }

    @Override
    public void onConnectionFailed(ConnectionResult connectionResult) {
        
    }

    private boolean servicesAvailable() {
        int resultCode = GooglePlayServicesUtil.isGooglePlayServicesAvailable(this);

        if (ConnectionResult.SUCCESS == resultCode) {
            return true;
        }
        else {
            GooglePlayServicesUtil.getErrorDialog(resultCode, this, 0).show();
            return false;
        }
    }
}

Android: Determining if a Wearable Device is Connected

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I’m playing around with developing an application that integrates with the new Android Wear API. In my case I don’t want to perform certain actions locally if a wearable device is connected. So this is how you can detect if a device is connected. You would have this code included in the Main Activity of your primary (phone) application:

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