为什么FusedLocationProviderClient不再提供位置了？

Question

我正在尝试使用FusedLocationProviderClient获取移动设备的位置。尽管花了一整天的时间来完成各自的任务，但我却找不到任何位置

这是我的代码（Java文件）：

import android.Manifest;
import android.content.pm.PackageManager;
import android.location.Location;
import android.os.Looper;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

import com.google.android.gms.location.FusedLocationProviderClient;
import com.google.android.gms.location.LocationCallback;
import com.google.android.gms.location.LocationRequest;
import com.google.android.gms.location.LocationResult;
import com.google.android.gms.location.LocationServices;
import com.google.android.gms.tasks.OnSuccessListener;

public class MainActivity extends AppCompatActivity {
    private static final int REQUEST_CODE = 1000;
    private TextView textView;
    private Button startButton, stopButton;

    private FusedLocationProviderClient fusedLocationProviderClient;
    private LocationRequest locationRequest;
    private LocationCallback locationCallback;

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);

        switch (requestCode) {
            case REQUEST_CODE: {
                if (grantResults.length > 0) {
                    if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {

                    } else if (grantResults[0] == PackageManager.PERMISSION_DENIED) {

                    }
                }
            }
        }
    }

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

        textView = findViewById(R.id.text_view);
        startButton = findViewById(R.id.button_start);
        stopButton = findViewById(R.id.button_stop);



        fusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(this);


        if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.ACCESS_FINE_LOCATION)) {
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, REQUEST_CODE);
        } else {
            buildLocationRequest();
            buildLocationCallBack();
        }

        fusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(this);

        startButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {


                if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED
                        && ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.ACCESS_COARSE_LOCATION )!= PackageManager.PERMISSION_GRANTED) {
                    ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, REQUEST_CODE);

                    return;
                }
                fusedLocationProviderClient.requestLocationUpdates(locationRequest, locationCallback, Looper.myLooper());
                startButton.setEnabled(!startButton.isEnabled());
                stopButton.setEnabled(!stopButton.isEnabled());

            }
        });

        stopButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED
                        && ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.ACCESS_COARSE_LOCATION )!= PackageManager.PERMISSION_GRANTED) {
                    ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, REQUEST_CODE);

                    return;
                }
                fusedLocationProviderClient.removeLocationUpdates(locationCallback);
                startButton.setEnabled(!startButton.isEnabled());
                stopButton.setEnabled(!stopButton.isEnabled());

            }
        });








    }

    private void buildLocationCallBack() {
        locationCallback = new LocationCallback()
        {
            @Override
            public void onLocationResult(LocationResult locationResult) {
                for(Location location: locationResult.getLocations()){
                    textView.setText(String.valueOf(location.getLatitude())+"/"+String.valueOf(location.getLongitude()));
                }

            }
        };
    }

    private void buildLocationRequest(){
        locationRequest = new LocationRequest();
        locationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
        locationRequest.setInterval(5000);
        locationRequest.setFastestInterval(3000);
        locationRequest.setSmallestDisplacement(10);
    }
}