Question

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！

Answer 1

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。

Answer 2

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？

每当进入特定的活动屏幕时，应用程序就会以“待定意图”崩溃

2 个答案: