FusedLocationApi.getLastLocation始终返回null

我在手机上尝试。它始终返回null。为什么？（已授予所有权限.ACCESS_COARSE_LOCATION ACCESS_FINE_LOCATION）

fusedLocationClient = LocationServices.getFusedLocationProviderClient(this);
    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)
            != PackageManager.PERMISSION_GRANTED &&
            ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION)
                    != PackageManager.PERMISSION_GRANTED) {
        return;
    }
    fusedLocationClient.getLastLocation()
            .addOnSuccessListener(this, new OnSuccessListener<Location>() {
                @Override
                public void onSuccess(Location location) {
                    if (location != null) {
                        Toast.makeText(MainActivity.this, "Location: "+location, Toast.LENGTH_SHORT).show();
                    }
                    else{
                        Toast.makeText(MainActivity.this, "null", Toast.LENGTH_SHORT).show();
                    }

            });```
依存关系：

dependencies { implementation fileTree(include: ['*.jar'], dir: 'libs') implementation 'com.android.support:appcompat-v7:28.0.0' implementation 'com.android.support.constraint:constraint-layout:1.1.3' testImplementation 'junit:junit:4.12' androidTestImplementation 'com.android.support.test:runner:1.0.2' androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2' implementation 'com.google.android.gms:play-services-location:16.0.0'}

表现：

问题来源：Stack Overflow