Android

Question

我知道有一些关于空白地图的问题，但答案始终是 API 关键问题。我知道这不是问题，因为如果我只使用标准的 MapsActivity 模板，在 Activity:

中使用以下运行，它就可以正常工作

SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                 .findFragmentById(R.id.map);
mapFragment.getMapAsync(this);

而Activity布局如下：

<FrameLayout android:id="@+id/container_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_below="@id/my_toolbar"
    xmlns:android="http://schemas.android.com/apk/res/android">
    <fragment xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:map="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/map"
        android:name="com.google.android.gms.maps.SupportMapFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MapsActivity" />

当我尝试拥有一个通用主机 Activity（为了单一 Activity 架构的目的）时出现问题，这需要我创建一个片段（而不是 Activity) 从中调用映射逻辑。当我这样做时，我得到一个空白屏幕而不是地图 - 但日志显示 GoogleMap 对象不为空并且调用了 onMapReady 回调。该应用程序没有崩溃，我也没有看到任何有启发性的错误。这是我的代码...

fragment_map.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MapFragment">

    <fragment xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:map="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/mapSubFragment"
        android:name="com.google.android.gms.maps.SupportMapFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MapFragment" />

</FrameLayout>

MapFragment.java

public class MapFragment extends Fragment implements OnMapReadyCallback, GoogleMap.OnInfoWindowClickListener {
    private GoogleMap mMap;

    public MapFragment() {
        //Not sure why this is necessary, boilerplate from Navigation editor
    }

    public static MapFragment newInstance() {
        //Not sure why this is necessary, boilerplate from Navigation editor
        MapFragment fragment = new MapFragment();
        return fragment;
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_map, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {    
        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        SupportMapFragment mapFragment = (SupportMapFragment) getChildFragmentManager()
                .findFragmentById(R.id.mapSubFragment);
        Log.i("Code", String.valueOf(R.id.mapSubFragment));
        mapFragment.getMapAsync(this);
    }

    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;
        Log.i("Code", String.valueOf(mMap == null));

        //Check if user has location permissions granted
        setupMap();
    }
    }

然后是宿主Actvity...

NavHostActivity.xml

public class NavHostActivity extends AppCompatActivity {

    private NavController navController;

    //Methods go here to inflate the toolbar
    
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_nav_host);

        navController = Navigation.findNavController(this, R.id.nav_host_fragment);

        Toolbar toolbar = findViewById(R.id.my_toolbar);
        setSupportActionBar(toolbar);

    }

    @Override
    public boolean onSupportNavigateUp() {
        // Allows NavigationUI to support proper up navigation or the drawer layout
        // drawer menu, depending on the situation.
        return navController.navigateUp();

    }
}

此主机的布局activity...

activity_nav_host.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".NavHostActivity">

    //Toolbar stuff goes here

    <fragment
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"

        app:defaultNavHost="true"
        app:navGraph="@navigation/nav_graph" />


</RelativeLayout>

最后我的清单包含这个：

<meta-data
            android:name="com.google.android.geo.API_KEY"
            android:value="@string/google_maps_key" />

感谢您的帮助，我很困惑！

Answer 1

天哪，我看到我的错误了。看起来我从 Google getting started documentation for Navigation.

为我的 activity_host_fragment.xml 复制了 xml

出于某种原因，其中包括：

android:layout_width="0dp"
android:layout_height="0dp"

我将“0dp”更改为 match_parent 并且地图出现了。看起来一切正常，但对于一个无限小的片段。

我会把这个问题留在这里，以防其他人盲目地从该文档复制或对从片段调用的地图片段的代码感兴趣（我找不到任何演练）。

Android - Google 即使调用了 onMapReady 且 GoogleMap 不为空，地图仍为空白

Android - Google map blank even though onMapReady is called and GoogleMap is not null

java

android-fragments

google-maps-android-api-2