Question

我是在Android上使用地图的初学者。当我尝试将以下语句添加到我的代码中时，我遇到了问题：

map = ((mapfragment) getfragmentmanager().findfragmentbyid(r.id.map)).getmap()

应用程序启动时会一直崩溃。有人可以帮我找到解决方案吗？

main.java

package com.example.myfirstapp;

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 final LatLng location= new LatLng(49.27645, -122.917587);
    private GoogleMap map; 

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

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


    @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;
    }

    public void onClick_Search(View view) {
        CameraUpdate update = CameraUpdateFactory.newLatLng(location);
        map.animateCamera(update);
        map.setMapType(GoogleMap.MAP_TYPE_SATELLITE);
    }
}

xml文件

<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"
    tools:context="com.example.myfirstapp.MainActivity$PlaceholderFragment" >

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

    <EditText
        android:id="@+id/Longitude"
        android:layout_width="110dp"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/Latitude"
        android:layout_alignParentTop="true"
        android:layout_toRightOf="@+id/Latitude"
        android:ems="10"
        android:hint="@string/Longitude" />

    <EditText
        android:id="@+id/Latitude"
        android:layout_width="110dp"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:ems="10"
        android:hint="@string/Latitude" />

    <Button
        android:id="@+id/Search"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:onClick="onClick_Search"
        android:text="@string/search" />

</RelativeLayout>

清单文件

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

    <uses-sdk
        android:minSdkVersion="11"
        android:targetSdkVersion="19" />

    <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"/>

    <uses-feature
        android:glEsVersion="0x00020000"
        android:required="true"/>

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >

        <meta-data android:name="com.google.android.gms.version"
           android:value="@integer/google_play_services_version" />

        <activity
            android:name="com.example.myfirstapp.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="AIzaSyCR9Zwp4m9nrKNWmfd1jAoeC8icski08_c" />

    </application>

</manifest>

logcat的

05-16 12:07:10.600: E/AndroidRuntime(1007): FATAL EXCEPTION: main
05-16 12:07:10.600: E/AndroidRuntime(1007): Process: com.example.myfirstapp, PID: 1007
05-16 12:07:10.600: E/AndroidRuntime(1007): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myfirstapp/com.example.myfirstapp.MainActivity}: java.lang.NullPointerException
05-16 12:07:10.600: E/AndroidRuntime(1007):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
05-16 12:07:10.600: E/AndroidRuntime(1007):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
05-16 12:07:10.600: E/AndroidRuntime(1007):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
05-16 12:07:10.600: E/AndroidRuntime(1007):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
05-16 12:07:10.600: E/AndroidRuntime(1007):     at android.os.Handler.dispatchMessage(Handler.java:102)
05-16 12:07:10.600: E/AndroidRuntime(1007):     at android.os.Looper.loop(Looper.java:136)
05-16 12:07:10.600: E/AndroidRuntime(1007):     at android.app.ActivityThread.main(ActivityThread.java:5017)
05-16 12:07:10.600: E/AndroidRuntime(1007):     at java.lang.reflect.Method.invokeNative(Native Method)
05-16 12:07:10.600: E/AndroidRuntime(1007):     at java.lang.reflect.Method.invoke(Method.java:515)
05-16 12:07:10.600: E/AndroidRuntime(1007):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
05-16 12:07:10.600: E/AndroidRuntime(1007):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
05-16 12:07:10.600: E/AndroidRuntime(1007):     at dalvik.system.NativeStart.main(Native Method)
05-16 12:07:10.600: E/AndroidRuntime(1007): Caused by: java.lang.NullPointerException
05-16 12:07:10.600: E/AndroidRuntime(1007):     at com.example.myfirstapp.MainActivity.onCreate(MainActivity.java:27)
05-16 12:07:10.600: E/AndroidRuntime(1007):     at android.app.Activity.performCreate(Activity.java:5231)
05-16 12:07:10.600: E/AndroidRuntime(1007):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
05-16 12:07:10.600: E/AndroidRuntime(1007):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
05-16 12:07:10.600: E/AndroidRuntime(1007):     ... 11 more

Answer 1

看起来你想要Map内的Fragment。您需要使用MapView或扩展MapFragment本身。

http://developer.android.com/reference/com/google/android/gms/maps/MapView.html

你的min sdk是11.动作栏可以从api 11级获得。所以没有必要延长ActionBarActivity。您可以扩展标准Activity。

将片段中的布局更改为

<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"
    tools:context="com.example.myfirstapp.MainActivity$PlaceholderFragment" >


    <EditText
        android:id="@+id/Longitude"
        android:layout_width="110dp"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/Latitude"
        android:layout_alignParentTop="true"
        android:layout_toRightOf="@+id/Latitude"
        android:ems="10"
        android:hint="@string/Longitude" />

    <EditText
        android:id="@+id/Latitude"
        android:layout_width="110dp"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:ems="10"
        android:hint="@string/Latitude" />

    <Button
        android:id="@+id/Search"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:onClick="onClick_Search"
        android:text="@string/search" />
    <com.google.android.gms.maps.MapView
        android:layout_above="@+id/Search"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/map"
    />

 </RelativeLayout>

在你的片段中

public class MyFragment extends Fragment {
MapView mapView;
GoogleMap map;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment2, container, false);
// Initialize otheres view here 
// Gets the MapView from the XML layout and creates it

try {
    MapsInitializer.initialize(getActivity());
} catch (GooglePlayServicesNotAvailableException e) {
    Log.e("Address Map", "Could not initialize google play", e);
}

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();
}
}

编辑：

事实上，我没有看到片段。

所以改为

public class MainActivity extends Activity {  
private final LatLng location= new LatLng(49.27645, -122.917587);
private GoogleMap map; 

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

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

注意：getMap()可以返回null。您应该在初始化Map对象之前检查google平台服务的可用性。

引用文档

GoogleMap只能在底层使用getMap（）获取加载了地图系统，并且片段中的基础视图存在。该类自动初始化地图系统和视图; 但是，因为这样，你就无法保证准备就绪取决于Google Play服务APK的可用性。如果一个 GoogleMap不可用，getMap（）将返回null。

Answer 2

这是因为 findViewById（）在 activity_main 布局中进行搜索，而地图位于片段的布局 fragment_main 中。

在片段的onCreateView()方法中移动该段代码

<强>例如

//...

View rootView = inflater.inflate(R.layout.fragment_main, container, false);
Button buttonClick = (Button)rootView.findViewById(R.id.button);
buttonClick.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        onButtonClick((Button) view);
    }
});

请注意，现在您可以通过rootView视图访问它：

Button buttonClick = (Button)rootView.findViewById(R.id.button);

否则你会再次 NullPointerException 。

map =（（mapfragment）getfragmentmanager（）。findfragmentbyid（r.id.map））。getmap（）一直给我一个错误

2 个答案: