android - 位置一开始是空的

Question

我正在重新设计我的最后一个问题，这个问题没有答案，我已经重写了 Google's BasicLocation 之后的问题.

我的主要 Activity 定义为:

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {
//    private LocationCallback locationCallback;
//     private FusedLocationProviderClient mFusedLocationClient;
    private FusedLocationProviderClient mFusedLocationClient;
    protected Location mLastLocation;
    private static final int REQUEST_PERMISSIONS_REQUEST_CODE = 34;
    private static final String TAG = MainActivity.class.getSimpleName();



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.drawer_main);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        mFusedLocationClient = LocationServices.getFusedLocationProviderClient(this);
        SectionsPagerAdapter sectionsPagerAdapter = new SectionsPagerAdapter(this, getSupportFragmentManager());
        ViewPager viewPager = findViewById(R.id.view_pager);
        viewPager.setAdapter(sectionsPagerAdapter);
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        NavigationView navigationView = findViewById(R.id.nav_view);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();
        navigationView.setNavigationItemSelectedListener(this);

        ImageButton leftNav = findViewById(R.id.left_nav);
        ImageButton rightNav = findViewById(R.id.right_nav);
        leftNav.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int tab = viewPager.getCurrentItem();
                if (tab > 0) {
                    tab--;
                    viewPager.setCurrentItem(tab);
                } else if (tab == 0) {
                    viewPager.setCurrentItem(tab);
                }
            }
        });

        rightNav.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int tab = viewPager.getCurrentItem();
                tab++;
                viewPager.setCurrentItem(tab);
            }
        });

    }
    @Override
    public void onStart() {
        super.onStart();
        if (!checkPermissions()) {
            requestPermissions();
        } else {
            getLastLocation();
        }
    }

with latlang.[Lat,Lang] 在一个单独的文件中:

public class latlang {
    public static double Lat;
    public static double Lang;
}

位置文件，即 viewpager 中的第一个 fragment ，定义为:

public class SunFragment extends Fragment {

    List<SunSession> sunsList;
    Typeface sunfont;


    //to be called by the MainActivity
    public SunFragment() {
        // Required empty public constructor
    }

    // Keys for storing activity state.
//  private static final String KEY_CAMERA_POSITION = "camera_position";
    private static final String KEY_LOCATION_NAME = "location_name";
    public String location;//="No location name found";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // Retrieve location and camera position from saved instance state.
        if (savedInstanceState != null) {
            location = savedInstanceState.getCharSequence(KEY_LOCATION_NAME).toString();
            System.out.println("OnCreate location  "+location);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View rootView = inflater.inflate(R.layout.fragment_sun, container, false);
        onSaveInstanceState(new Bundle());
        //SecondFragment secondFragment = new SecondFragment();
        //secondFragment.getDeviceLocation();

        RecyclerView rv = rootView.findViewById(R.id.rv_recycler_view);
        rv.setNestedScrollingEnabled(false);
        rv.setHasFixedSize(true);
        //MyAdapter adapter = new MyAdapter(new String[]{"Today", "Golden Hour", "Blue Hour", "Civil Twilight", "Nautical Twilight", "Astronomical Twilight", "Hello", "World"});
        //rv.setAdapter(adapter);
        LinearLayoutManager llm = new LinearLayoutManager(getActivity());
        rv.setLayoutManager(llm);
        System.out.println("location  "+location);



   /*
     Reversegeocoding location
     */
        String location="No location name found";
        String errorMessage = "";
        List<Address> addresses = null;

        Geocoder geocoder = new Geocoder(getContext(), Locale.getDefault());
        try {
            addresses = geocoder.getFromLocation(
                    latlang.Lat,
                    latlang.Lang,
                    1);
        } catch (IOException ioException) {
            // Catch network or other I/O problems.
            errorMessage = getString(R.string.service_not_available);
            // Log.e(TAG, errorMessage, ioException);
            if (getView() != null){
                Snackbar.make(getView(), errorMessage, Snackbar.LENGTH_LONG).show();
            }
        } catch (IllegalArgumentException illegalArgumentException) {
            // Catch invalid latitude or longitude values.
            errorMessage = getString(R.string.invalid_lat_long_used);
            if (getView() != null){
                Snackbar.make(getView(),
                        "Illegal Latitude = " + latlang.Lat + ", Longitude = " +
                                latlang.Lang, Snackbar.LENGTH_LONG).show();
            }
        }
        if (addresses == null || addresses.size() == 0) {
            if (errorMessage.isEmpty()) {
                System.out.println("Adress Empty No Address Found");// Snackbar.LENGTH_LONG).show();
                location = "Lat:"+latlang.Lat+" Lang: "+latlang.Lang;
            }
        } else {
            location = addresses.get(0).getAddressLine(0);//+", "+ addresses.get(0).getLocality();
        /* for(int i = 0; i <= addresses.get(0).getMaxAddressLineIndex(); i++) {
          location = addresses.get(0).getAddressLine(i);
        }*/
        }

从 logcat 可以明显看出这个问题:

I/System.out: location  null
 I/Google Maps Android API: Google Play services package version: 17785022
 I/Choreographer: Skipped 31 frames!  The application may be doing too much work on its main thread.
 I/System.out: Position:0
 I/System.out: Position:1
 I/System.out: Position:2
 I/zygote: Do full code cache collection, code=202KB, data=177KB
 I/zygote: After code cache collection, code=129KB, data=91KB
 I/zygote: JIT allocated 56KB for compiled code of void android.view.View.<init>(android.content.Context, android.util.AttributeSet, int, int)
 I/zygote: Background concurrent copying GC freed 44415(2MB) AllocSpace objects, 7(136KB) LOS objects, 49% free, 3MB/6MB, paused 294us total 102.458ms
 I/System.out: Position:3
 I/System.out: Position:4
 I/zygote: Do partial code cache collection, code=193KB, data=126KB
 I/zygote: After code cache collection, code=193KB, data=126KB
 I/zygote: Increasing code cache capacity to 1024KB
 I/zygote: JIT allocated 71KB for compiled code of void android.widget.TextView.<init>(android.content.Context, android.util.AttributeSet, int, int)
 I/zygote: Compiler allocated 4MB to compile void android.widget.TextView.<init>(android.content.Context, android.util.AttributeSet, int, int)
 E/MainActivity: Latit: 37.42342342342342

这表明，在开始时，位置为空，

I/System.out: location null

然后创建sunfragment的recyclerview

 I/System.out: Position:0
 I/System.out: Position:1
 I/System.out: Position:2

然后我得到了位置:

E/MainActivity: Latit: 37.42342342342342

完整代码链接:https://drive.google.com/file/d/1pMl_3Lf76sy82C0J4b-9ta4jbSHonJ2y/view?usp=sharing

是否有可能在创建 sunfragment 的 oncreateview 之前先获取位置？

Answer 1

我发现您的代码有问题(我可能错了):

1. 为什么 latlang 的字段是static？看起来他们不应该这样做。

2. 在 SunFragment.onCreate() 处，如果 savedInstanceState != null，您正在读取 location。 savedInstanceState 仅当保存此 fragment 的 Activity 从已保存状态恢复时才不为空。它可能根本不会发生。

3. 您应该使用 fragment 的参数(Bundle)将初始数据传递给 fragment

4. 您应该为 latlang 实现 Parcelable 接口(interface)，以便能够通过 Bundle 传递自定义类

我认为这还不是全部，但对我来说似乎足以让这段代码无法按预期工作