这是我正在等待开始我的Udacity Advanced Android App Development课程的一个有趣的个人项目。我正在自己学习“待定意图和通知”，因此我对这一切真的很陌生。
当我尝试在离开活动时重新进入食欲活动时，该应用似乎崩溃了。第一次进入“食欲活动”时效果很好。这是我发现的错误：
致命异常：主要 流程：com.example.zzyzj.eloteroman，PID：26757 java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法“ void android.widget.TextView.setText（java.lang.CharSequence）” com.example.zzyzj.eloteroman.AppetiteActivity.onConnected（AppetiteActivity.java:82）
这是我的GitHub，可以更轻松地访问：（https://github.com/PoetryHorizon/eloteroMan2）
这是AppetiteActivity.java：
public class AppetiteActivity extends AppCompatActivity implements GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener, com.google.android.gms.location.LocationListener {
private static final String TAG = "AppetiteActivity";
private TextView mLatitudeTextView;
private TextView mLongitudeTextView;
private GoogleApiClient mGoogleApiClient;
private Location mLocation;
public LocationManager mLocationManager;
private LocationRequest mLocationRequest;
private com.google.android.gms.location.LocationListener listener;
private long UPDATE_INTERVAL = 2 * 1000; /* 10 secs */
private long FASTEST_INTERVAL = 2000; /* 2 sec */
private LocationManager locationManager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.appetite_layout);
mLatitudeTextView = (TextView) findViewById((R.id.latitude_textview));
mLongitudeTextView = (TextView) findViewById((R.id.longitude_textview));
mGoogleApiClient = new GoogleApiClient.Builder(this)
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.addApi(LocationServices.API)
.build();
mLocationManager = (LocationManager)this.getSystemService(Context.LOCATION_SERVICE);
checkLocation(); //check whether location service is enable or not in your phone
}
@Override
public void onConnected(Bundle bundle) {
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, 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;
}
startLocationUpdates();
mLocation = LocationServices.FusedLocationApi.getLastLocation(mGoogleApiClient);
if(mLocation == null){
startLocationUpdates();
}
if (mLocation != null) {
mLatitudeTextView.setText(String.valueOf(mLocation.getLatitude()));
mLongitudeTextView.setText(String.valueOf(mLocation.getLongitude()));
} else {
Toast.makeText(this, "Location not Detected", Toast.LENGTH_SHORT).show();
}
}
@Override
public void onConnectionSuspended(int i) {
Log.i(TAG, "Connection Suspended");
mGoogleApiClient.connect();
}
@Override
public void onConnectionFailed(ConnectionResult connectionResult) {
Log.i(TAG, "Connection failed. Error: " + connectionResult.getErrorCode());
}
@Override
protected void onStart() {
super.onStart();
if (mGoogleApiClient != null) {
mGoogleApiClient.connect();
}
}
@Override
protected void onStop() {
super.onStop();
if (mGoogleApiClient.isConnected()) {
mGoogleApiClient.disconnect();
}
}
protected void startLocationUpdates() {
// Create the location request
mLocationRequest = LocationRequest.create()
.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY)
.setInterval(UPDATE_INTERVAL)
.setFastestInterval(FASTEST_INTERVAL);
// Request location updates
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, 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;
}
LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient,
mLocationRequest, this);
Log.d("reque", "--->>>>");
}
@Override
public void onLocationChanged(Location location) {
String msg = "Updated Location: " +
Double.toString(location.getLatitude()) + "," +
Double.toString(location.getLongitude());
mLatitudeTextView.setText(String.valueOf(location.getLatitude()));
mLongitudeTextView.setText(String.valueOf(location.getLongitude() ));
Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();
// You can now create a LatLng Object for use with maps
LatLng latLng = new LatLng(location.getLatitude(), location.getLongitude());
}
private boolean checkLocation() {
if(!isLocationEnabled())
showAlert();
return isLocationEnabled();
}
private void showAlert() {
final AlertDialog.Builder dialog = new AlertDialog.Builder(this);
dialog.setTitle("Enable Location")
.setMessage("Your Locations Settings is set to 'Off'.\nPlease Enable Location to " +
"use this app")
.setPositiveButton("Location Settings", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface paramDialogInterface, int paramInt) {
Intent myIntent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
startActivity(myIntent);
}
})
.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface paramDialogInterface, int paramInt) {
}
});
dialog.show();
}
private boolean isLocationEnabled() {
locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
return locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER) ||
locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
}
}
非常感谢您的帮助和时间，我非常感谢！
答案 0 :(得分：0)
您的布局文件appetite_layout.xml包含LinearLayout，但没有其他内容。在onCreate()中，您可以这样做：
setContentView(R.layout.appetite_layout);
mLatitudeTextView = (TextView) findViewById((R.id.latitude_textview));
mLongitudeTextView = (TextView) findViewById((R.id.longitude_textview));
mLatitudeTextView和mLongitudeTextView都将是null，因为在布局文件中没有具有这些ID的TextView。
稍后，您尝试在这些setText()引用上调用null。
答案 1 :(得分：0)
从您的github链接中，我发现了appetite_layout.xml：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
</LinearLayout>
此布局xml文件中没有任何内容，因此发生了错误，但是在vendor_layout.xml文件中：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#b3ffff">
<ImageView
android:layout_width="203dp"
android:layout_height="203dp"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="49dp"
android:src="@drawable/vendor_activity_logo" />
<TextView
android:id="@+id/latitude"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="@+id/longitude_textview"
android:layout_alignParentStart="true"
android:layout_marginStart="67dp"
android:text="@string/latitude"
android:textSize="30sp" />
<TextView
android:id="@+id/latitude_textview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/latitude"
android:layout_marginLeft="10dp"
android:layout_toRightOf="@+id/latitude"
android:textSize="20sp" />
<TextView
android:id="@+id/longitude"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignStart="@+id/latitude"
android:layout_marginBottom="156dp"
android:text="@string/longitude"
android:textSize="30sp" />
<TextView
android:id="@+id/longitude_textview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/longitude"
android:layout_marginLeft="10dp"
android:layout_toRightOf="@+id/longitude"
android:textSize="20sp"/>
</RelativeLayout>
所以也许您拼写布局文件名称错误？