我已经阅读了一些相关主题，但我们无法解决我的问题。由于我处于学习阶段，我正在尝试实施Google的位置服务教程。问题是，我没有使用＆＃34; LocationRequest.b（）＆＃34;代码中的任何位置，但按下“开始更新”按钮时会出现以下错误。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
弹出错误的Sepcific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();
}
}}
答案 0 :(得分：8)
问题是您已经为protected LocationRequest mLocationRequest;声明了一个变量，并且您正在LocationRequest mLocationRequest = new LocationRequest();方法中使用同名createLocationRequest()重新创建并初始化它。所以只需用
mLocationRequest = new LocationRequest();
<强> 编辑：
您的mListener可能为空。所以只为你的类实现接口
public class MainActivity extends Activity implements ConnectionCallbacks, OnConnectionFailedListener, LocationListener {
现在使用
LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient,mLocationRequest,this);
以及
LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, this);
答案 1 :(得分：0)
您的mLocation似乎为null且未获得结果。确保您已在Mainfiest中添加了正确的权限。