java - 异常 : Attempt to invoke virtual method 'int com.google.android.gms.location.LocationRequest.b()' on a null object reference

Question

我已经阅读了一些相关主题，但未能解决我的问题。由于我处于学习阶段，我正在尝试实现谷歌的定位服务教程。问题是，我没有在代码中的任何地方使用“LocationRequest.b()”，但是当我按下“开始更新”按钮时出现以下错误。该应用程序随后崩溃。请让我知道我做错了什么。

错误:

Exception: Attempt to invoke virtual method 'int com.google.android.gms.location.LocationRequest.b()' on a null object reference

具体报错代码位置:

protected void startLocationUpdates() {
            LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient,mLocationRequest,mListener);
 }

MainActivity.java 的完整代码:

public class MainActivity extends Activity implements ConnectionCallbacks, OnConnectionFailedListener {
    protected GoogleApiClient mGoogleApiClient;

    /**
     * Represents a geographical location.
     */
    protected Location mCurrentLocation;
    protected LocationRequest mLocationRequest;
    protected static final String TAG = "basic-location-sample";

    //UI Widgets
    protected Button mStartUpdatesButton;
    protected Button mStopUpdatesButton;
    protected TextView mLastUpdateTimeTextView;
    protected TextView mLatitudeTextView;
    protected TextView mLongitudeTextView;


    boolean mRequestingLocationUpdates;
    protected String mLastUpdateTime;

    // keys
    protected final static String REQUESTING_LOCATION_UPDATES_KEY = "requesting-location-updates-key";
    protected final static String LOCATION_KEY = "location-key";
    protected final static String LAST_UPDATED_TIME_STRING_KEY = "last-updated-time-string-key";

   public LocationListener mListener;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_main);
               // Locate the UI widgets.
        mStartUpdatesButton = (Button) findViewById(R.id.start_updates_button);
        mStopUpdatesButton = (Button) findViewById(R.id.stop_updates_button);
        mLatitudeTextView = (TextView) findViewById(R.id.latitude_text);
        mLongitudeTextView = (TextView) findViewById(R.id.longitude_text);
        mLastUpdateTimeTextView = (TextView) findViewById(R.id.last_update_time_text);
        mRequestingLocationUpdates = false;
        mLastUpdateTime = "";
        buildGoogleApiClient();
        //LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient,mLocationRequest,mListener);

        updateValuesFromBundle(savedInstanceState);


   }

    private void updateValuesFromBundle(Bundle savedInstanceState) {
        Log.i(TAG, "Updating values from bundle");
        if (savedInstanceState != null) {
            // Update the value of mRequestingLocationUpdates from the Bundle, and
            // make sure that the Start Updates and Stop Updates buttons are
            // correctly enabled or disabled.
            if (savedInstanceState.keySet().contains(REQUESTING_LOCATION_UPDATES_KEY)) {
                mRequestingLocationUpdates = savedInstanceState.getBoolean(
                        REQUESTING_LOCATION_UPDATES_KEY);
                setButtonsEnabledState();
            }

            // Update the value of mCurrentLocation from the Bundle and update the
            // UI to show the correct latitude and longitude.
            if (savedInstanceState.keySet().contains(LOCATION_KEY)) {
                // Since LOCATION_KEY was found in the Bundle, we can be sure that
                // mCurrentLocationis not null.
                mCurrentLocation = savedInstanceState.getParcelable(LOCATION_KEY);
            }

            // Update the value of mLastUpdateTime from the Bundle and update the UI.
            if (savedInstanceState.keySet().contains(LAST_UPDATED_TIME_STRING_KEY)) {
                mLastUpdateTime = savedInstanceState.getString(
                        LAST_UPDATED_TIME_STRING_KEY);
            }
            updateUI();
        }
    }

    protected synchronized void buildGoogleApiClient() {
        Log.i(TAG, "Building GoogleApiClient");
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener((OnConnectionFailedListener) this)
                .addApi(LocationServices.API)
                .build();

        createLocationRequest();

    }

    protected void createLocationRequest() {
        LocationRequest mLocationRequest = new LocationRequest();
        mLocationRequest.setInterval(10000);
        mLocationRequest.setFastestInterval(5000);
        mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
    }

    public void startUpdatesButtonHandler(View view) {
        if (!mRequestingLocationUpdates) {
            mRequestingLocationUpdates = true;
            setButtonsEnabledState();
            startLocationUpdates();
        }
    }

    public void stopUpdatesButtonHandler(View view) {
        if (mRequestingLocationUpdates) {
            mRequestingLocationUpdates = false;
            setButtonsEnabledState();
            stopLocationUpdates();
        }
    }

    protected void startLocationUpdates() {
        LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient,mLocationRequest,mListener);
    }

       private void setButtonsEnabledState() {
        if (mRequestingLocationUpdates) {
            mStartUpdatesButton.setEnabled(false);
            mStopUpdatesButton.setEnabled(true);
        } else {
            mStartUpdatesButton.setEnabled(true);
            mStopUpdatesButton.setEnabled(false);
        }
    }

    private void updateUI() {
        if(mCurrentLocation!=null){
            mLatitudeTextView.setText(String.valueOf(mCurrentLocation.getLatitude()));
            mLongitudeTextView.setText(String.valueOf(mCurrentLocation.getLongitude()));
            mLastUpdateTimeTextView.setText(mLastUpdateTime);
        }}

    /**
     * Removes location updates from the FusedLocationApi.
     */
    protected void stopLocationUpdates() {
        // It is a good practice to remove location requests when the activity is in a paused or
        // stopped state. Doing so helps battery performance and is especially
        // recommended in applications that request frequent location updates.


        LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, mListener);
    }

    @Override
    protected void onStart() {
        super.onStart();
        mGoogleApiClient.connect();
    }


    @Override
    public void onResume() {
        super.onResume();
        // Within {@code onPause()}, we pause location updates, but leave the
        // connection to GoogleApiClient intact.  Here, we resume receiving
        // location updates if the user has requested them.

        if (mGoogleApiClient.isConnected() && mRequestingLocationUpdates) {
            startLocationUpdates();
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        // Stop location updates to save battery, but don't disconnect the GoogleApiClient object.
        stopLocationUpdates();
    }

    @Override
    public void onConnected(Bundle connectionHint) {
        Log.i(TAG, "Connected to GoogleApiClient");
        if (mCurrentLocation == null) {
            mCurrentLocation = LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient);
            mLastUpdateTime = DateFormat.getTimeInstance().format(new Date());
            updateUI();
        }
        if (mRequestingLocationUpdates) {
            startLocationUpdates();
        }
//        mLastLocation = LocationServices.FusedLocationApi.getLastLocation(
//                mGoogleApiClient);
//       if (mLastLocation!= null) {
//            mLatitudeText.setText(String.valueOf(mLastLocation.getLatitude()));
//            mLongitudeText.setText(String.valueOf(mLastLocation.getLongitude()));
//       }
    }

    public void onLocationChanged(Location location) {
        mCurrentLocation = location;
        mLastUpdateTime = DateFormat.getTimeInstance().format(new Date());
        updateUI();
        Toast.makeText(this, getResources().getString(R.string.location_updated_message),
                Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onConnectionSuspended(int i) {
        Log.i(TAG, "Connection suspended");
        mGoogleApiClient.connect();
    }

    @Override
    public void onConnectionFailed(ConnectionResult result) {
        Log.i(TAG, "Connection failed: ConnectionResult.getErrorCode() = " + result.getErrorCode());
    }

    public void onDisconnected() {
        Log.i(TAG, "Disconnected");
    }

    public void onSaveInstanceState(Bundle savedInstanceState) {

        savedInstanceState.putBoolean(REQUESTING_LOCATION_UPDATES_KEY,
                mRequestingLocationUpdates);
        savedInstanceState.putParcelable(LOCATION_KEY, mCurrentLocation);
        savedInstanceState.putString(LAST_UPDATED_TIME_STRING_KEY, mLastUpdateTime);
        super.onSaveInstanceState(savedInstanceState);
    }

   @Override
   protected void onStop() {
       super.onStop();
       if (mGoogleApiClient.isConnected()) {
           mGoogleApiClient.disconnect();
        }
    }}

Answer 1

问题是您已经为 protected LocationRequest mLocationRequest; 声明了一个变量，并且您正在使用相同的名称 LocationRequest mLocationRequest = new LocationRequest(); 重新创建和初始化它createLocationRequest() 方法。所以只需将其更改为

 mLocationRequest = new LocationRequest();

编辑:

您的mListener 可能为空。所以只需为您的类实现接口(interface)

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

现在使用

LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient,mLocationRequest,this);

也为

LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, this);