纬度和经度返回Null

Question

我正在尝试打印纬度和经度，以及我的应用程序中的加速计读数。但是，当我尝试在我的Main Activity类中使用我的GPS类的纬度和经度时，它总是返回null。有人能告诉我我做错了什么吗？我尝试了无数不同的方法（互联网上充满了它们），但似乎没有解决我的问题。感谢。

MainActivity.java

package com.explorer.extractor;

//import packages

import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TableLayout;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.util.Calendar;


public class MainActivity extends ActionBarActivity implements SensorEventListener,OnClickListener {

    GPSTracker gps;

    Button button1;
    Button button2;

    private SensorManager mSensorManager;
    Sensor accelerometer;

    private static final String TAG = MainActivity.class.getName();

    private static final String FILENAME = "newgps.txt"; //file where data is written


    //layout variables
    TableLayout t1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //initialize sensor manager
        mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
        //initialize accelerometer
        accelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
        //mSensorManager.registerListener(this, accelerometer, SensorManager.SENSOR_DELAY_FASTEST);

        t1 = (TableLayout) findViewById(R.id.main_table);
        button1 = (Button) findViewById(R.id.button1);
        button2 = (Button) findViewById(R.id.button2);

        button1.setOnClickListener(this);
        button2.setOnClickListener(this);
    }

    public void onAccuracyChanged(Sensor sensor, int accuracy){}

    /**onResume() registers the accelerometer for listening
     * to the events
     */
    /*
    protected void onResume(){
        super.onResume();
        mSensorManager.registerListener(this, accelerometer, SensorManager.SENSOR_DELAY_FASTEST);
    }
    */
    /*
    protected void onPause(){
        super.onPause();
        mSensorManager.unregisterListener(this);
    }
    */

    public void onSensorChanged(SensorEvent event){
       //if sensor status result is unreliable return
        if (event.accuracy == SensorManager.SENSOR_STATUS_UNRELIABLE){
            return;
        }

        Sensor sensor = event.sensor;

        //check sensor type
        if (sensor.getType() == Sensor.TYPE_ACCELEROMETER){
            //assign directions
            float x = event.values[0];
            float y = event.values[1];
            float z = event.values[2];

            try {
                //write to text file the x, y, and z values each type a sensor detects change
                writeToFile(Float.toString(x), Float.toString(y), Float.toString(z));
                Log.i("LIMA", "hey lily it got here!");

                /*
                String textFromFileString = readFromFile();
                TableRow tr = new TableRow(this);
                if(count%2!=0) {
                    tr.setBackgroundColor(Color.GRAY);
                }
                tr.setId(100 + count);
                tr.setLayoutParams(new TableRow.LayoutParams(TableRow.LayoutParams.MATCH_PARENT, TableRow.LayoutParams.WRAP_CONTENT));

                //show data read from file
                dataReading = new TextView(this);
                dataReading.setId(200 + count);
                dataReading.setText(textFromFileString);
                dataReading.setPadding(2, 0, 5, 0);
                dataReading.setTextColor(Color.WHITE);
                tr.addView(dataReading);
                //finally add data to table row
                t1.addView(tr, new TableLayout.LayoutParams(ActionBar.LayoutParams.MATCH_PARENT, ActionBar.LayoutParams.WRAP_CONTENT));
                count++;
                Log.i("LIMA","Add row. There are now " + t1.getChildCount()+"rows");
                */
            }catch (IOException e) {
                e.printStackTrace();
            }
        }

    }

    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.button1:
                mSensorManager.registerListener(this, accelerometer, SensorManager.SENSOR_DELAY_FASTEST);
                Log.i("LIME","I pressed start!!!");
                break;
            case R.id.button2:
                mSensorManager.unregisterListener(this);
                //gps.stopUsingGPS();
                Log.i("LIME","I pressed stop!!!");
        }
    }

    /**
     * writeToFile: writes data recordings of accelerometer to text file
     * @param x
     * @param y
     * @param z
     * @throws IOException
     */
    void writeToFile(String x, String y, String z) throws IOException {

        double latVal;
        double longVal;

        String s;

        //get exact instance of time in which call to write is being made
        Calendar c = Calendar.getInstance();
        //create string to print to text using values in parameter.
        GPSTracker track = new GPSTracker(this);
        latVal = track.getLatitude();
        Log.i("test", "this is the latitude" + latVal);
        longVal = track.getLongitude();
        s = "Time: " + c.get(Calendar.HOUR) + ":" + c.get(Calendar.MINUTE) + ":" + c.get(Calendar.SECOND) + ":" + c.get(Calendar.MILLISECOND) + " Coordinates: " + "x: " + x + " y: " + y + " z: " + z + " Latitude: " + latVal + " Longitude: " + longVal + "\n\r";

            //s = "Time: " + c.get(Calendar.HOUR) + ":" + c.get(Calendar.MINUTE) + ":" + c.get(Calendar.SECOND) + ":" + c.get(Calendar.MILLISECOND) + " Coordinates: " + "x: " + x + " y: " + y + " z: " + z + "\n\r";
            //Log.i("shucks", "it never got the gps.");



        try {
            //append new string to file
            FileOutputStream fos = openFileOutput(FILENAME, Context.MODE_APPEND | Context.MODE_WORLD_READABLE);
            //FileWriter fstream = new FileWriter(file, true);
            //BufferedWriter bw = new BufferedWriter(fstream);
            OutputStreamWriter bw = new OutputStreamWriter(fos);
            bw.append(s);
            bw.append("\n\r");
            bw.close();
            Log.i("LIMA","IT GOT HERE 2");
        } catch(IOException e) {
            Log.e(TAG, "File write failed: " + e.toString());
        }
    }

    /**
    private String readFromFile(){
        String ret = "";
        try {
            //open text file to read from
            InputStream inputStream = openFileInput(FILENAME);
            if (inputStream != null) {
                InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
                BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
                String receiveString = "";
                StringBuilder stringBuilder = new StringBuilder();

                while ((receiveString = bufferedReader.readLine()) != null) {
                    //continue appending to stringBuilder until you've reached the end of file
                    stringBuilder.append(receiveString);
                }
                inputStream.close();
                ret = stringBuilder.toString();
            }
        } catch (FileNotFoundException e) {
            Log.e(TAG, "File not found: " + e.toString());
        } catch (IOException e) {
            Log.e(TAG, "Can not read file: " + e.toString());
        }
        return ret;
    }
     */
}

GPSTracker.java

package com.explorer.extractor;

import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.os.IBinder;

public class GPSTracker extends Service implements LocationListener {

    // saving the context for later use
    public final Context mContext;

    // if GPS is enabled
    boolean isGPSEnabled = false;
    // if Network is enabled
    boolean isNetworkEnabled = false;
    // if Location co-ordinates are available using GPS or Network
    public boolean isLocationAvailable = false;

    // Location and co-ordinates coordinates
    Location mLocation;
    double mLatitude;
    double mLongitude;

    // Minimum time fluctuation for next update (in milliseconds)
    private static final long TIME = 0;
    // Minimum distance fluctuation for next update (in meters)
    private static final long DISTANCE = 0;

    // Declaring a Location Manager
    public LocationManager mLocationManager;

    public GPSTracker(Context context) {
        this.mContext = context;
        mLocationManager = (LocationManager) mContext
                .getSystemService(LOCATION_SERVICE);

    }

    /**
     * Returs the Location
     *
     * @return Location or null if no location is found
     */
    public Location getLocation() {
        try {

            // Getting GPS status
            isGPSEnabled = mLocationManager
                    .isProviderEnabled(LocationManager.GPS_PROVIDER);


            // If we are reaching this part, it means GPS was not able to fetch
            // any location
            // Getting network status
            isNetworkEnabled = mLocationManager
                    .isProviderEnabled(LocationManager.NETWORK_PROVIDER);

            if (isNetworkEnabled) {
                mLocationManager.requestLocationUpdates(
                        LocationManager.NETWORK_PROVIDER, TIME, DISTANCE, this);
                if (mLocationManager != null) {
                    mLocation = mLocationManager
                            .getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
                    if (mLocation != null) {
                        mLatitude = mLocation.getLatitude();
                        mLongitude = mLocation.getLongitude();
                        isLocationAvailable = true; // setting a flag that
                        // location is available
                        return mLocation;
                    }
                }
            }
            // If reaching here means, we were not able to get location neither
            // from GPS not Network,

        } catch (Exception e) {
            e.printStackTrace();
        }
        // if reaching here means, location was not available, so setting the
        // flag as false
        isLocationAvailable = false;
        return null;
    }

    /**
     * get latitude
     *
     * @return latitude in double
     */
    public double getLatitude() {
        if (mLocation != null) {
            mLatitude = mLocation.getLatitude();
        }
        return mLatitude;
    }

    /**
     * get longitude
     *
     * @return longitude in double
     */
    public double getLongitude() {
        if (mLocation != null) {
            mLongitude = mLocation.getLongitude();
        }
        return mLongitude;
    }

    /**
     * close GPS to save battery
     */
    public void closeGPS() {
        if (mLocationManager != null) {
            mLocationManager.removeUpdates(GPSTracker.this);
        }
    }

    /**
     * Updating the location when location changes
     */
    @Override
    public void onLocationChanged(Location location) {
        mLatitude = location.getLatitude();
        mLongitude = location.getLongitude();
    }

    @Override
    public void onProviderDisabled(String provider) {
    }

    @Override
    public void onProviderEnabled(String provider) {
    }

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {
    }

    @Override
    public IBinder onBind(Intent arg0) {
        return null;
    }

}

Answer 1

您是否在清单中声明了此权限？

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"></uses-permission>