android - 在 Android 中使用 GoogleMaps 出现 NullPointerException

Question

我的代码在我的代码中的这一行抛出 NullPointerException:

map=((MapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap()

我可以看到它在 LogCat 中抛出异常。我已经多次尝试解决这个问题，并且我已经阅读了该论坛上的所有类似问题。我尝试了一些解决方案，但没有成功。当我注释掉该行时，我会显示 Google map ，但是当我尝试在代码中获取该 fragment 时，我仍然遇到相同的异常。

这是我的代码:

package cs.exmpl;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;

import com.google.android.gms.maps.CameraUpdate;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.model.LatLng;

public class MainActivity extends ActionBarActivity {
    private GoogleMap map;
    private final LatLng loc=new LatLng(566544, 556554);

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

            map=((MapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();

        //SupportMapFragment mapFrag = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
       // map = mapFrag.getMap();



            map.setMapType(GoogleMap.MAP_TYPE_SATELLITE);
        CameraUpdate up=CameraUpdateFactory.newLatLngZoom(loc, 14);
        map.animateCamera(up);






        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment()).commit();
        }

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container,
                    false);
            return rootView;
        }
    }

}

这是我的 XML:

<RelativeLayout 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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="cs.exmpl.MainActivity$PlaceholderFragment" >

    <TextView
        android:id="@+id/header"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

    <fragment 
          android:id="@+id/map"
          android:name="com.google.android.gms.maps.MapFragment"
          android:layout_below="@+id/header"
          android:layout_width="match_parent"
          android:layout_height="match_parent"/>

</RelativeLayout>

Answer 1

getMap() 可能返回 null

引用文档

A GoogleMap can only be acquired using getMap() when the underlying maps system is loaded and the underlying view in the fragment exists. This class automatically initializes the maps system and the view; however you cannot be guaranteed when it will be ready because this depends on the availability of the Google Play services APK. If a GoogleMap is not available, getMap() will return null.

在初始化 GoogleMap 对象之前检查 Google Play 服务的可用性。

检查主题检查 Google Play 服务

http://developer.android.com/training/location/retrieve-current.html

编辑:

tools:context="cs.exmpl.MainActivity$PlaceholderFragment"

当您在 Activity 中初始化它时，MapFragment 看起来也处于 fragment 布局中。使用MapView跟随

Android - android.view.InflateException: Binary XML file line #8: Error inflating class fragment

或者扩展MapFragment而不是Fragment。

编辑3:

示例:

activity_main.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="cs.exmpl.MainActivity"
    tools:ignore="MergeRootFrame" />

fragment_main.xml

<RelativeLayout 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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="cs.exmpl.MainActivity$PlaceholderFragment" >

    <TextView
        android:id="@+id/header"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

   <com.google.android.gms.maps.MapView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/map"
    />


</RelativeLayout>

MainActivity.java

public class MainActivity extends ActionBarActivity {

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

        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment()).commit();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {
        MapView mapView;
        GoogleMap map;
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_main, container, false);
        // Gets the MapView from the XML layout and creates it

        MapsInitializer.initialize(getActivity());


        switch (GooglePlayServicesUtil.isGooglePlayServicesAvailable(getActivity()) )
        {
        case ConnectionResult.SUCCESS:
          Toast.makeText(getActivity(), "SUCCESS", Toast.LENGTH_SHORT).show();
          mapView = (MapView) v.findViewById(R.id.map);
          mapView.onCreate(savedInstanceState);
          // Gets to GoogleMap from the MapView and does initialization stuff
          if(mapView!=null)
          {
          map = mapView.getMap();
          map.getUiSettings().setMyLocationButtonEnabled(false);
          map.setMyLocationEnabled(true);
          CameraUpdate cameraUpdate = CameraUpdateFactory.newLatLngZoom(new LatLng(43.1, -87.9), 10);
          map.animateCamera(cameraUpdate);
          }
          break;
        case ConnectionResult.SERVICE_MISSING: 
          Toast.makeText(getActivity(), "SERVICE MISSING", Toast.LENGTH_SHORT).show();
          break;
        case ConnectionResult.SERVICE_VERSION_UPDATE_REQUIRED: 
          Toast.makeText(getActivity(), "UPDATE REQUIRED", Toast.LENGTH_SHORT).show();
          break;
        default: Toast.makeText(getActivity(), GooglePlayServicesUtil.isGooglePlayServicesAvailable(getActivity()), Toast.LENGTH_SHORT).show();
        }




        // Updates the location and zoom of the MapView

        return v;
        }

        @Override
        public void onResume() {
        mapView.onResume();
        super.onResume();
        }
        @Override
        public void onDestroy() {
        super.onDestroy();
        mapView.onDestroy();
        }
        @Override
        public void onLowMemory() {
        super.onLowMemory();
        mapView.onLowMemory();
        }
        }

}

list

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="cs.exmpl"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="19" />
    <uses-feature
        android:glEsVersion="0x00020000"
        android:required="true"/> 

     <uses-permission android:name="android.permission.INTERNET"/>
     <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
     <uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES"/>
     <!-- The following two permissions are not required to use
     Google Maps Android API v2, but are recommended. -->
     <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
     <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="cs.exmpl.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
               <meta-data
    android:name="com.google.android.maps.v2.API_KEY"
    android:value="YOUR API KEY FROM GOOGLE API CONSOLE"/>
        <meta-data android:name="com.google.android.gms.version"
          android:value="@integer/google_play_services_version" />
    </application>

</manifest>

固定在设备上