java - 纬度和经度为空

Question

我正在开发一个应用程序，获取用户的当前位置并将其显示在 map 上，以及屏幕上的纬度和经度，到目前为止一切都很顺利， map 显示我当前的位置，并使用此代码在屏幕上显示纬度和经度

@Override
public void onLocationChanged(Location location) {

    TextView tvLocation = (TextView) findViewById(R.id.tv_location);

    // Getting latitude of the current location
    double latitude = location.getLatitude();

    // Getting longitude of the current location
    double longitude = location.getLongitude();

    // Creating a LatLng object for the current location
    LatLng latLng = new LatLng(latitude, longitude);

    // Showing the current location in Google Map
    googleMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));

    // Zoom in the Google Map
    googleMap.animateCamera(CameraUpdateFactory.zoomTo(15));

    // Setting latitude and longitude in the TextView tv_location
    tvLocation.setText("Latitude:" +  latitude  + ", Longitude:"+ longitude );

}

当我想在服务器上发送这个纬度和经度时出现问题，它抛出 NUll 指针异常

 01-04 23:27:38.759 29286-29286/io.xgear.geotag E/AndroidRuntime: FATAL
 EXCEPTION: main
  Process: io.xgear.geotag, PID: 29286
  java.lang.NullPointerException
      at io.xgear.geotag.MainActivity$GeoTagTask.<init>(MainActivity.java:234)
      at io.xgear.geotag.MainActivity$1.onClick(MainActivity.java:181)
      at android.view.View.performClick(View.java:4633)
      at android.view.View$PerformClick.run(View.java:19270)
      at android.os.Handler.handleCallback(Handler.java:733)
      at android.os.Handler.dispatchMessage(Handler.java:95)
      at android.os.Looper.loop(Looper.java:146)
      at android.app.ActivityThread.main(ActivityThread.java:5602)
      at java.lang.reflect.Method.invokeNative(Native Method)
      at java.lang.reflect.Method.invoke(Method.java:515)
      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
      at dalvik.system.NativeStart.main(Native Method)

这是获取要发送的纬度和经度的代码

 public class GeoTagTask extends AsyncTask<Void, Void, Boolean> {
        private final String shopCode;
       Location location;
        private String lat = Double.toString(location.getLatitude());
        private String lng = Double.toString(location.getLongitude());


        private boolean isConnect;
        GeoTagTask(String shopId) {
            shopCode = shopId;
            isConnect = false;

        }

        @Override
        protected Boolean doInBackground(Void... params) {
            boolean res = false;
     try {
                ContentValues nameValuePairs = new ContentValues();
                nameValuePairs.put("Id", shopCode);
                nameValuePairs.put("lat", lat);
                nameValuePairs.put("lng", lng);
         //Toast.makeText(getApplicationContext(), "Your Location is - \nLat: " + lat + "\nLong: " + lng, Toast.LENGTH_LONG).show();
               Log.i("Latitude", lat+"");

                Post post = new Post(getApplicationContext());
                String result = "";
//                isConnect = post.isConnected();
  //              if(isConnect) {
                    result = post.doPost(nameValuePairs);
                    jsonObj = new JSONObject(result);
                    Log.i("Result", result+"");
                    if(jsonObj.getInt("success") == 1)
                        res = true;
    //            }

            } catch (JSONException e) {
                e.printStackTrace();
            }
            return res;
        }

这是完整的代码

package io.xgear.geotag;


import android.Manifest;
import android.app.Dialog;
import android.app.FragmentTransaction;
import android.content.pm.PackageManager;
import android.location.Criteria;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.support.v4.app.ActivityCompat;
import android.support.v4.app.FragmentActivity;
import android.view.Menu;
import android.widget.TextView;
import android.support.v4.app.Fragment;

import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesUtil;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.GoogleMapOptions;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;

import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.annotation.TargetApi;
import android.content.ContentValues;
import android.os.AsyncTask;
import android.os.Build;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.InputType;
import android.text.TextUtils;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import org.json.JSONException;
import org.json.JSONObject;



import io.xgear.geotag.helper.Post;

public class MainActivity extends FragmentActivity implements LocationListener {
    GoogleMap googleMap;
    private GeoTagTask mAuthTask = null;
    GPSTracker gps;
    private JSONObject jsonObj;

    // UI references.
    private EditText txtShopCode;
    private EditText lblAddress;
    private View mProgressView;
    private View mGeoTagForm;
    private Button btnGeoTag;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        txtShopCode = (EditText) findViewById(R.id.txtShopCode);
        btnGeoTag = (Button) findViewById(R.id.btnGeoTag);
        mGeoTagForm = (View) findViewById(R.id.geoTagForm);
        mProgressView = findViewById(R.id.geoTagProgress);

        // Getting Google Play availability status
        int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(getBaseContext());

        // Showing status
        if (status != ConnectionResult.SUCCESS) { // Google Play Services are not available

            int requestCode = 10;
            Dialog dialog = GooglePlayServicesUtil.getErrorDialog(status, this, requestCode);
            dialog.show();

        } else { // Google Play Services are available

            // Getting reference to the SupportMapFragment of activity_main.xml
            SupportMapFragment fm = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);

            // Getting GoogleMap object from the fragment
            googleMap = fm.getMap();

            // Enabling MyLocation Layer of Google Map
            googleMap.setMyLocationEnabled(true);

            // Getting LocationManager object from System Service LOCATION_SERVICE
            LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);

            // Creating a criteria object to retrieve provider
            Criteria criteria = new Criteria();

            // Getting the name of the best provider
            String provider = locationManager.getBestProvider(criteria, true);

            // Getting Current Location
            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;
            }
            Location location = locationManager.getLastKnownLocation(provider);

            if(location!=null){
                onLocationChanged(location);
            }
            locationManager.requestLocationUpdates(provider, 20000, 0, this);
        }

        btnGeoTag.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View arg0) {
                String shopid = txtShopCode.getText().toString();
                boolean cancel = false;
                View focusView = null;

               //txtShopCode.setInputType(InputType.TYPE_CLASS_NUMBER);

                if (TextUtils.isEmpty(shopid)) {
                    txtShopCode.setError(getString(R.string.error_field_required));
                    focusView = txtShopCode;
                    cancel = true;

                }
                else {


                    showProgress(true);
                    mAuthTask = new GeoTagTask(shopid);
                    mAuthTask.execute((Void) null);
                }
            }

        });

    }

//


//    public void btnGeoTag_Click(View v){
//
//    }
    @TargetApi(Build.VERSION_CODES.HONEYCOMB_MR2)
    public void showProgress(final boolean show) {
        // On Honeycomb MR2 we have the ViewPropertyAnimator APIs, which allow
        // for very easy animations. If available, use these APIs to fade-in
        // the progress spinner.
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB_MR2) {
            int shortAnimTime = getResources().getInteger(android.R.integer.config_shortAnimTime);

            mGeoTagForm.setVisibility(show ? View.GONE : View.VISIBLE);
            mGeoTagForm.animate().setDuration(shortAnimTime).alpha(
                    show ? 0 : 1).setListener(new AnimatorListenerAdapter() {
                @Override
                public void onAnimationEnd(Animator animation) {
                    mGeoTagForm.setVisibility(show ? View.GONE : View.VISIBLE);
                }
            });

            mProgressView.setVisibility(show ? View.VISIBLE : View.GONE);
            mProgressView.animate().setDuration(shortAnimTime).alpha(
                    show ? 1 : 0).setListener(new AnimatorListenerAdapter() {
                @Override
                public void onAnimationEnd(Animator animation) {
                    mProgressView.setVisibility(show ? View.VISIBLE : View.GONE);
                }
            });
        } else {
            // The ViewPropertyAnimator APIs are not available, so simply show
            // and hide the relevant UI components.
            mProgressView.setVisibility(show ? View.VISIBLE : View.GONE);
            mGeoTagForm.setVisibility(show ? View.GONE : View.VISIBLE);
        }
    }

    public class GeoTagTask extends AsyncTask<Void, Void, Boolean> {
        private final String shopCode;
       Location location;
        private String lat = Double.toString(location.getLatitude());
        private String lng = Double.toString(location.getLongitude());


        private boolean isConnect;
        GeoTagTask(String shopId) {
            shopCode = shopId;
            isConnect = false;

        }

        @Override
        protected Boolean doInBackground(Void... params) {
            boolean res = false;
     try {
                ContentValues nameValuePairs = new ContentValues();
                nameValuePairs.put("Id", shopCode);
                nameValuePairs.put("lat", lat);
                nameValuePairs.put("lng", lng);
         //Toast.makeText(getApplicationContext(), "Your Location is - \nLat: " + lat + "\nLong: " + lng, Toast.LENGTH_LONG).show();
               Log.i("Latitude", lat+"");

                Post post = new Post(getApplicationContext());
                String result = "";
//                isConnect = post.isConnected();
  //              if(isConnect) {
                    result = post.doPost(nameValuePairs);
                    jsonObj = new JSONObject(result);
                    Log.i("Result", result+"");
                    if(jsonObj.getInt("success") == 1)
                        res = true;
    //            }

            } catch (JSONException e) {
                e.printStackTrace();
            }
            return res;
        }

        @Override
        protected void onPostExecute(final Boolean success) {
            mAuthTask = null;
            showProgress(false);

            if (success) {
//                Intent intent = new Intent(LoginActivity.this, MainActivity.class);
//                intent.putExtra("jsonObj", jsonObj.toString());
//                startActivity(intent);
                txtShopCode.getText().clear();
                txtShopCode.requestFocus();
                Toast.makeText(getBaseContext(), "Your shop is geo tagged ", Toast.LENGTH_LONG).show();

            } else {
//                if(isConnect){
//                    mPasswordView.setError(getString(R.string.error_incorrect_password));
//                    mPasswordView.requestFocus();

//                }
//                else
                    Toast.makeText(getBaseContext(), R.string.geoTagError, Toast.LENGTH_LONG).show();
            }
        }

        @Override
        protected void onCancelled() {
            mAuthTask = null;
            showProgress(false);
        }
    }


    @Override
    public void onLocationChanged(Location location) {

        TextView tvLocation = (TextView) findViewById(R.id.tv_location);

        // Getting latitude of the current location
        double latitude = location.getLatitude();

        // Getting longitude of the current location
        double longitude = location.getLongitude();

        // Creating a LatLng object for the current location
        LatLng latLng = new LatLng(latitude, longitude);

        // Showing the current location in Google Map
        googleMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));

        // Zoom in the Google Map
        googleMap.animateCamera(CameraUpdateFactory.zoomTo(15));

        // Setting latitude and longitude in the TextView tv_location
        tvLocation.setText("Latitude:" +  latitude  + ", Longitude:"+ longitude );

    }

    @Override
    public void onProviderDisabled(String provider) {
        // TODO Auto-generated method stub
    }

    @Override
    public void onProviderEnabled(String provider) {
        // TODO Auto-generated method stub
    }

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {
        // TODO Auto-generated method stub
    }

//    @Override
//    public boolean onCreateOptionsMenu(Menu menu) {
//        // Inflate the menu; this adds items to the action bar if it is present.
//        getMenuInflater().inflate(R.menu.activity_main, menu);
//        return true;
//    }
}

更新我已在 GeoTagTask 中添加了这些行，按钮正在工作，应用程序没有崩溃，但我不确定如果位置更改它是否会工作，因为

 if( location != null){
            onLocationChanged(location);
       }
     locationManager.requestLocationUpdates(provider, 20000, 0, this);

给我错误。

我添加的行

LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
        Criteria criteria = new Criteria();
        String provider = locationManager.getBestProvider(criteria, true);

        Location location = locationManager.getLastKnownLocation(provider);

Answer 1

问题

问题出在 GeoTagTask 内部，

Location location;
private String lat = Double.toString(location.getLatitude());
private String lng = Double.toString(location.getLongitude());

您正在访问未初始化的变量。

解决方案

将 onCreate location 设置为全局变量，

public class MainActivity extends FragmentActivity implements LocationListener {
    Location location;
    void onCreate() {
        ....
        location = locationManager.getLastKnownLocation(provider);
        ....
    }
}

在GeoTagTask中使用全局变量，

public class GeoTagTask extends AsyncTask<Void, Void, Boolean> {
        private String lat = Double.toString(location.getLatitude());
        private String lng = Double.toString(location.getLongitude());
        ...
}