Fused Location Provider Client 始终将第一个位置返回为 null答案

【问题标题】：Fused Location Provider Client always returns first location as nullFused Location Provider Client 始终将第一个位置返回为 null
【发布时间】：2020-03-30 23:47:52
【问题描述】：

我有一个带有按钮的活动，单击该按钮时，应显示该位置。但是第一次点击总是返回null，第二次点击返回正确的信息。我尝试使用延迟，但这只会延迟警报对话框的创建，第一次单击按钮时的第一个值仍然为空。

public class MainActivity extends AppCompatActivity {
    private FusedLocationProviderClient fusedLocationClient;
    private Double longitude, latitude;
    private Float accuracy;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        fusedLocationClient = LocationServices.getFusedLocationProviderClient(this);

        Button testButton = findViewById(R.id.test_button);
        testButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getCurrentLocation();
                new AlertDialog.Builder(MainActivity.this)
                        .setTitle("Current Location")
                        .setMessage("Location: " + latitude +", "+ longitude +
                                "\nAccuracy: " + String.format(Locale.getDefault(),"%.2f", accuracy) +"m")
                        .setNegativeButton(android.R.string.cancel, null)
                        .show();
                }
            }
        });
    }

    private void getCurrentLocation() {
    fusedLocationClient.getLastLocation()
            .addOnSuccessListener(this, new OnSuccessListener<Location>() {
                    @Override
                    public void onSuccess(Location location) {
                        // Get last known location, and check for null.
                        if(location!=null) {
                            latitude = location.getLatitude();
                            longitude = location.getLongitude();
                            accuracy = location.getAccuracy();
                        }
                    }
                });
    }

【问题讨论】：

标签： android android-location

【解决方案1】：

尝试使变量受保护，这样做：

 protected FusedLocationProviderClient fusedLocationClient;
 protected Double longitude, latitude;
 protected Float accuracy;

取而代之的是：

private FusedLocationProviderClient fusedLocationClient;
private Double longitude, latitude;
private Float accuracy;

【讨论】：

不，没有任何改变。还是同样的问题。

【解决方案2】：

在 Location 可用后构建 AlertDialog，如下所示：

private void getCurrentLocation() {
    fusedLocationClient.getLastLocation()
            .addOnSuccessListener(this, new OnSuccessListener<Location>() {
                @Override
                public void onSuccess(Location location) {
                    // Get last known location, and check for null.
                    if (location != null) {
                        latitude = location.getLatitude();
                        longitude = location.getLongitude();
                        accuracy = location.getAccuracy();
                        new AlertDialog.Builder(context)
                                .setTitle("Current Location")
                                .setMessage("Location: " + latitude + ", " + longitude +
                                        "\nAccuracy: " + String.format(Locale.getDefault(), "%.2f", accuracy) + "m")
                                .setNegativeButton(android.R.string.cancel, null)
                                .show();

                    }
                }
            });
}

【讨论】：