java - App is not opening , though no errors..! -

i have tried make simple app . first app in android , not new java . app has customised background , sound (song) playing on homescreen . builds . no errors @ all..!!! have taken care of warnings..

but app doesn't work on device (i dont use emulator..!!) says , "unfortunately [appname] has stopped "..

why????

here java code..:

package com.exmple.worth;  import android.app.activity; import android.media.mediaplayer; import android.os.bundle; import android.view.view; import android.widget.button;  public class mainactivity extends activity {      mediaplayer bfmv = mediaplayer.create(mainactivity.this, r.raw.saf ) ;     button b1 ;     @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);         b1 = (button) findviewbyid(r.id.b1) ;         bfmv.start() ;          b1.setonclicklistener(new view.onclicklistener() {              @override             public void onclick(view v) {                 // todo auto-generated method stub                 bfmv.stop() ;             }         });     }  } 

here xml file :

<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="${packagename}.${activityclass}"      android:background="@drawable/qwe" >"      <textview         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="@string/hello_world" />      <button         android:id="@+id/b1"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_alignparentbottom="true"         android:layout_centerhorizontal="true"         android:layout_marginbottom="14dp"         android:text="pause" />  </relativelayout> 

and here android manifest :

    <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"     package="com.exmple.worth"     android:versioncode="1"     android:versionname="1.0" >      <uses-sdk         android:minsdkversion="13"         android:targetsdkversion="18" />      <application         android:allowbackup="true"         android:icon="@drawable/ic_launcher"         android:label="@string/app_name"         android:theme="@style/apptheme" >         <activity             android:name="com.exmple.worth.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>  </manifest> 

i tried code. way instantiate bfmv wrong.

mediaplayer bfmv = mediaplayer.create(mainactivity.this, r.raw.saf ) ; 

it should this: on outer class declare object:

mediaplayer bfmv; 

and on oncreate method instantiate it:

bfmv = mediaplayer.create(mainactivity.this, r.raw.saf ) ; 

the reason force close context mainactivity.this null before oncreate called.