适用于Media Player的Android Singleton类

Question

我有以下代码

静态课程

import android.content.Context;
import android.media.MediaPlayer;
import android.os.Handler;
import android.view.View;
import android.widget.SeekBar;
import android.widget.TextView;

import java.util.concurrent.TimeUnit;

public class CustomMedia {

    public static MediaPlayer mediaPlayer,englishmediaPlayer;
    public static TextView duration,englishduration;
    public static double timeElapsed = 0, finalTime = 0;
    public static double englishtimeElapsed = 0, englishfinalTime = 0;
    public static int forwardTime = 2000, backwardTime = 2000;
    public static Handler durationHandler = new Handler();
    public static int englishforwardTime = 2000, englishbackwardTime = 2000;
    public static Handler englishdurationHandler = new Handler();
    public static SeekBar seekbar,englishseekbar;


    public static void initializeViews(View v,Context context,Integer songName){

        mediaPlayer = MediaPlayer.create(context,songName);


        finalTime = mediaPlayer.getDuration();


        duration = (TextView)v.findViewById(R.id.song_duration_display);
        seekbar = (SeekBar)v.findViewById(R.id.media_seekbar);



        seekbar.setMax((int) finalTime);
        seekbar.setClickable(false);


    }

    // play mp3 song
    public static void play() {

        mediaPlayer.start();



        timeElapsed = mediaPlayer.getCurrentPosition();
        seekbar.setProgress((int) timeElapsed);
        durationHandler.postDelayed(updateSeekBarTime, 100);

    }
    //handler to change seekBarTime
    private static Runnable updateSeekBarTime = new Runnable() {
     public void run() {
            //get current position
            timeElapsed = mediaPlayer.getCurrentPosition();
            //set seekbar progress
            seekbar.setProgress((int) timeElapsed);
            //set time remaing
            double timeRemaining = finalTime - timeElapsed;
            duration.setText(String.format("%d min, %d sec", TimeUnit.MILLISECONDS.toMinutes((long) timeRemaining), TimeUnit.MILLISECONDS.toSeconds((long) timeRemaining) - TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes((long) timeRemaining))));

            //repeat yourself that again in 100 miliseconds
            durationHandler.postDelayed(this, 100);
        }
    };

    // pause mp3 song
    public static void pause() {
        mediaPlayer.pause();
    }

    // go forward at forwardTime seconds
    public static void forward(View view) {
        //check if we can go forward at forwardTime seconds before song endes
        if ((timeElapsed + forwardTime) <= finalTime) {
            timeElapsed = timeElapsed + forwardTime;

            //seek to the exact second of the track
            mediaPlayer.seekTo((int) timeElapsed);
        }
    }
    // go backwards at backwardTime seconds
    public static void rewind(View view) {
        //check if we can go back at backwardTime seconds after song starts
        if ((timeElapsed - backwardTime) > 0) {
            timeElapsed = timeElapsed - backwardTime;

            //seek to the exact second of the track
            mediaPlayer.seekTo((int) timeElapsed);
        }
    }

    public static void stop(View view) {

        mediaPlayer.seekTo(0);
        mediaPlayer.pause();
    }
}

音乐片段

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;



public class OldMusic extends Fragment {
    View v;
  ImageView play;
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

         v = inflater.inflate(R.layout.old_music, container, false);
        play= (ImageView) v.findViewById(R.id.btn_play);

        return v;
    }



    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        CustomMedia.initializeViews(v,getContext(),R.raw.somya);
        play.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                CustomMedia.play();
            }
        });

    }

    @Override
    public void onPause() {
        super.onPause();
    }


}

我已经为medial播放器创建了静态类，所以我可以在很多片段中调用它。但是我得到了以下空指针异常。任何人都可以帮我解决这个问题吗？

更新

FATAL EXCEPTION: main
                                                                               java.lang.NullPointerException
                                                                                   at com.example.asd.learn.OldMusic.onActivityCreated(OldMusic.java:34)
                                                                                   at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1970)
                                                                                   at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1041)
                                                                                   at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1197)
                                                                                   at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
                                                                                   at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1562)
                                                                                   at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:483)
                                                                                   at android.os.Handler.handleCallback(Handler.java:615)
                                                                                   at android.os.Handler.dispatchMessage(Handler.java:92)
                                                                                   at android.os.Looper.loop(Looper.java:137)
                                                                                   at android.app.ActivityThread.main(ActivityThread.java:4960)
                                                                                   at java.lang.reflect.Method.invokeNative(Native Method)
                                                                                   at java.lang.reflect.Method.invoke(Method.java:511)
                                                                                   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038)
                                                                                   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)
                                                                                   at dalvik.system.NativeStart.main(Native Method)