java - GetMap() return null on Android with Google Maps API v2 -

i have problems google maps api v2. have tried many tutorials , searched many answers (include stack overflow) have found not work. can draw map xml tag <fragment>. no problem, works. when try map in mainactivity.java getmap() return null , don't know why.

mainactivity.java

package com.example.testmaps;  import android.app.activity; import android.os.bundle;  import com.google.android.gms.maps.googlemap; import com.google.android.gms.maps.mapfragment; import com.google.android.gms.maps.model.latlng; import com.google.android.gms.maps.model.markeroptions;  public class mainactivity extends activity {  private googlemap mmap; @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);       mmap = ((mapfragment) getfragmentmanager().findfragmentbyid(r.id.map)).getmap();     //here mmap null     mmap.addmarker(new markeroptions()             .position(new latlng(10, 10))             .title("hello world"));     } } 

activity_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"     tools:context=".mainactivity" >      <fragment            android:id="@+id/map"           android:layout_width="match_parent"           android:layout_height="match_parent"           android:name="com.google.android.gms.maps.mapfragment"/>  </relativelayout>  

manifest.xml

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"     package="com.example.testmaps"     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"/> <!-- following 2 permissions not required use      google maps android api v2, 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" >         <activity             android:name="com.example.testmaps.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="my_key" />         <meta-data     android:name="com.google.android.gms.version"     android:value="@integer/google_play_services_version" />     </application>  </manifest> 

add api key

<meta-data         android:name="com.google.android.maps.v2.api_key"         android:value="aizasya_ywwmn2h21nvvzuiqcpqsipzoalaix7z" />      // place api key 

and can write below

 android.support.v4.app.fragmentmanager myfm = getsupportfragmentmanager();  final supportmapfragment mymapf = (supportmapfragment) myfm.findfragmentbyid(r.id.mapview);  googlemap = mymapf.getmap(); 

my layout file like

<?xml version="1.0" encoding="utf-8"?> <relativelayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:paddingbottom="@dimen/activity_vertical_margin" android:paddingleft="@dimen/activity_horizontal_margin" android:paddingright="@dimen/activity_horizontal_margin" android:paddingtop="@dimen/activity_horizontal_margin" >  <fragment     android:id="@+id/mapview"     android:layout_width="match_parent"     android:name="com.google.android.gms.maps.supportmapfragment"     android:layout_height="fill_parent"     android:layout_alignparenttop="true" />  <button     android:padding="5dp"     android:layout_margin="10dp"     android:background="@drawable/button"     android:id="@+id/refreshmap"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_alignparentbottom="true"     android:layout_centerhorizontal="true"     android:text="@string/button_refresh_map" />   </relativelayout>