Question

我正在使用Android中的Googl Maps API v2。

MapExample.java代码

 public class MapExample extends FragmentActivity {  
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);             
}

main.xml代码

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

清单文件代码

<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="17" />

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

<permission
    android:name="com.example.android.mapexample.permission.MAPS_RECEIVE"
    android:protectionLevel="signature"/>

                                                                                                                                                                                                                                                                         <uses_permission                                                                                 android:name="com.example.android.mapexample.permission.MAPS_RECEIVE"/>
<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" />    
<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" >

    <meta-data
android:name="com.google.android.maps.v2.API_KEY"
android:value="My API_KEY"/>

    <activity
        android:name=".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>


</application>

我在模拟器中运行此代码它在模拟器中显示一条消息并在LogCat中显示警告

消息：您的某些应用程序所依赖的Google Play服务不受您的设备支持。请通过ok按钮与制造商联系以获取帮助。警告：Google Play签名无效。

点击该按钮时出现错误

03-02 13:17:30.746: D/AndroidRuntime(905): Shutting down VM
03-02 13:17:30.746: W/dalvikvm(905): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
03-02 13:17:30.776: E/AndroidRuntime(905): FATAL EXCEPTION: main
03-02 13:17:30.776: E/AndroidRuntime(905): java.lang.NullPointerException
03-02 13:17:30.776: E/AndroidRuntime(905):  at android.app.Instrumentation.execStartActivity(Instrumentation.java:1409)
03-02 13:17:30.776: E/AndroidRuntime(905):  at android.app.Activity.startActivityForResult(Activity.java:3351)
03-02 13:17:30.776: E/AndroidRuntime(905):  at android.app.Activity.startActivityForResult(Activity.java:3312)
03-02 13:17:30.776: E/AndroidRuntime(905):  at android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:817)
03-02 13:17:30.776: E/AndroidRuntime(905):  at android.app.Activity.startActivity(Activity.java:3522)
03-02 13:17:30.776: E/AndroidRuntime(905):  at android.app.Activity.startActivity(Activity.java:3490)
03-02 13:17:30.776: E/AndroidRuntime(905):  at com.google.android.gms.internal.e$2.onClick(Unknown Source)
03-02 13:17:30.776: E/AndroidRuntime(905):  at android.view.View.performClick(View.java:4084)
03-02 13:17:30.776: E/AndroidRuntime(905):  at android.view.View$PerformClick.run(View.java:16966)
03-02 13:17:30.776: E/AndroidRuntime(905):  at android.os.Handler.handleCallback(Handler.java:615)
03-02 13:17:30.776: E/AndroidRuntime(905):  at android.os.Handler.dispatchMessage(Handler.java:92)
03-02 13:17:30.776: E/AndroidRuntime(905):  at android.os.Looper.loop(Looper.java:137)
03-02 13:17:30.776: E/AndroidRuntime(905):  at android.app.ActivityThread.main(ActivityThread.java:4745)
03-02 13:17:30.776: E/AndroidRuntime(905):  at java.lang.reflect.Method.invokeNative(Native Method)
03-02 13:17:30.776: E/AndroidRuntime(905):  at java.lang.reflect.Method.invoke(Method.java:511)
03-02 13:17:30.776: E/AndroidRuntime(905):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
03-02 13:17:30.776: E/AndroidRuntime(905):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-02 13:17:30.776: E/AndroidRuntime(905):  at dalvik.system.NativeStart.main(Native Method)

我该如何解决这个问题？