如何从“ onCreate（）”访问同一类的另一个方法中的Arraylist变量？

Question

I want to access an Arraylist variable ( mySongs ) declared globally and used in the onCreate() method in another method called btnNext() . The value of this variable is taken from another class using Intent .

But I'm not able to get the value of that variable in the btnNext() method.

Intent i = getIntent();
Bundle b = i.getExtras();
mySongs = (ArrayList) b.getParcelableArrayList("songlist");
position = b.getInt("pos",0);

It's giving a null pointer exception on this variable. When checked in the Log, it's showing 'null' in the method whereas when checked on Log outside the btnNext() method, it works fine.

public void btnNext(){
    Log.d("DATA", "songs"+mySongs);

    if(isRepeat==true || isShuffle==true)
    {
        isRepeat = false;
        btnRepeat.setImageResource(R.drawable.btn_repeat_default);

        isShuffle = false;
        btnShuffle.setImageResource(R.drawable.btn_shuffle_default);
    }
    mp.stop();
    mp.release();
    position = (position+1) % mySongs.size();
    Log.d("DATA", "p"+position);
    u = Uri.parse(mySongs.get(position).toString());
    mp = MediaPlayer.create(getApplicationContext(),u);
    displaySongName(position);
    mp.start();
    btnPlay.setImageResource(R.drawable.btn_pause);
    //Toast.makeText(this, "Method called", Toast.LENGTH_SHORT).show();
    Log.d("DATA", "p");    
}

What could be the problem?

Answer 1

replace this

mySongs = (ArrayList) b.getParcelableArrayList("songlist"); 

with this

mySongs = new ArrayList<Object>(b.getParcelableArrayList("songlist"));

Answer 2

Make it public static and you will be able to pass your ArrayList to Another Class. But, better way would be to use Serializable or Parcelable to pass it.

Use it

mySongs = new ArrayList<Object>(b.getParcelableArrayList("songlist"));

Answer 3

您在全局上声明了mySongs，但是是否在onCreate（）中创建了它的实例？

mySongs = new ArrayList(); ?