关于 android:MapView google maps api V2 看起来是空白的，只显示带有 /- 按钮的网格

import android.os.Bundle;
import android.app.Activity;

import com.google.android.gms.common.GooglePlayServicesUtil;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapView;
import com.google.android.gms.maps.MapsInitializer;

public class MainActivity extends Activity {
  GoogleMap map;
  MapView m;
  com.google.android.gms.maps.Projection projection;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
     setContentView(R.layout.activity_main);
     m=(MapView) findViewById(R.id.mapview);
    m.onCreate(savedInstanceState);
    map = m.getMap();
    if (map != null) {
        // The Map is verified. It is now safe to manipulate the map.

    }else{
        // check if google play service in the device is not available or out-dated.
        GooglePlayServicesUtil.isGooglePlayServicesAvailable(this);

        // nothing anymore, cuz android will take care of the rest (to remind user to update google play service).
    }

    try{map.getUiSettings().setMyLocationButtonEnabled(false);
    map.setMyLocationEnabled(true);
    }catch(Exception ex){ex.printStackTrace();}

    MapsInitializer.initialize(this);

}
@Override
public void onResume() {

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

   super.onLowMemory();
   m.onLowMemory();
}
 @Override
public void onSaveInstanceState(Bundle outState){
    super.onSaveInstanceState(outState);
     m.onSaveInstanceState(outState);
  }
}

<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=".MainActivity">

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

</RelativeLayout>

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

android:versionCode="1"
android:versionName="1.0">

<uses-sdk
    android:minSdkVersion="9"
    android:targetSdkVersion="15" />

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

<uses-permission android:name="com.example.voicesee.permission.MAPS_RECEIVE" />
<!– Copied from Google Maps Library/AndroidManifest.xml. –>
<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.voicesee.MainActivity"
        android:label="@string/app_name">
        <intent-filter>
           

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

     <meta-data
       android:name="com.google.android.maps.v2.API_KEY"
       android:value="AIzaSyAguDjIFiVWi18ll7Yh0oa8C7hWju1PUzI"/>

</application>

MapsInitializer.initialize(this);