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Android

Posted by Sambhav Anand
Sambhav Anand
2,010 Points

I am getting an error while trying to code a basic location app

I am getting the following error when I am trying to run my code:

Unable to start activity ComponentInfo{com.example.sambhav.location/com.example.sambhav.location.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.location.Location.toString()' on a null object reference

My main activity code is:

public class MainActivity extends ActionBarActivity
implements GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener{

    private Location mLastLocation;
    private GoogleApiClient mGoogleApiClient;
    private TextView mTextView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mTextView = (TextView) findViewById(R.id.textView);
        buildGoogleApiClient();

        mTextView.setText(mLastLocation.toString());
    }

    protected synchronized void buildGoogleApiClient() {
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .addApi(LocationServices.API)
                .build();
    }

    @Override
    public void onConnected(Bundle bundle) {
        mLastLocation = LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient);

    }

    @Override
    public void onConnectionSuspended(int i) {

    }

    @Override
    public void onConnectionFailed(ConnectionResult connectionResult) {

    }
}

1 Answer

Kristen Law
Kristen Law
16,244 Points
Kristen Law
Kristen Law
16,244 Points

The error you are getting is basically saying that you are trying to call toString() on a null Location object. This means that mLastLocation hasn't been initialized yet and you are trying to use it. Moving this line

mTextView.setText(mLastLocation.toString());

into onConnected() after it has been initialized may accomplish what you are looking for.

Sambhav Anand
Sambhav Anand
2,010 Points

then how do initialize it so that i can use it inside the onCreate() method.

Kristen Law
Kristen Law
16,244 Points

Why do you need to set the text of mTextView inside the onCreate() method? You can't initialize mLastLocation in the onCreate() method because you need to wait for the onConnected() function callback to get called before you can get the location.

Sambhav Anand
Sambhav Anand
2,010 Points

So how do I handle the callback

Kristen Law
Kristen Law
16,244 Points

Have you tried what I suggested in my first comment?

Sambhav Anand
Sambhav Anand
2,010 Points

Ya I tried. The error has gone but my code is not running. How/When does the onConnected() method get called so that it can change the text of my TextView

Kristen Law
Kristen Law
16,244 Points

You'll need to add mGoogleApiClient.connect() somewhere, preferably in the onStart() method. From the Accessing Google APIs documentation:

With the callback interfaces defined, you're ready to call connect(). To gracefully manage the lifecycle of the connection, you should call connect() during the activity's onStart() (unless you want to connect later), then call disconnect() during the onStop() method.