在fragment转换中出现java.lang.NullPointerException

最近学校让做个android音乐播放器，我跟着论坛的教学做到这里时会出现闪退的问题，不知道怎么解决，求助（我是小白，如果可以请说详细些，谢谢啦）

放置fragment的activity没有实现OnMainFragmentInteractionListener这个接口。
楼主如果不需要用到这个接口， 就把@Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof OnMainFragmentInteractionListener) {
mListener = (OnMainFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()

• " must implement OnFragmentInteractionListener"); } } 注释掉吧！！！ 另外 import static com.example.ycxh.atry.R.id.myMusicButton;

but = (Button)rootView.findViewById(myMusicButton);
这种写法实在不提倡

这个是出错的代码

package com.example.ycxh.atry;

import android.app.Fragment;
import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;

import static com.example.ycxh.atry.R.id.myMusicButton;

public class MainFragment extends Fragment {

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.fragment_main, container, false);


    but = (Button)rootView.findViewById(myMusicButton);                                                 //切换至我的音乐Fragment
            but.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            mListener.onMainFragmentInteraction(AppConstant.PlayerMsg.CHANGE_TO_MY_MUSIC_FRAGMENT);
        }
    });
    return rootView;
}

      public interface OnMainFragmentInteractionListener {
    // TODO: Update argument type and name
   // void onFragmentInteraction(int message);

    void onMainFragmentInteraction(int message);

}

空指针异常一般都是最容易解决的。
你看看报的错误是对应那一行的代码，这一行代码中的那个对象是空指针异常的原因。
检查这个对象为空的原因以及该对象在上下文的使用。

mListener.onMainFragmentInteraction(AppConstant.PlayerMsg.CHANGE_TO_MY_MUSIC_FRAGMENT);
mListener这个变量没定义吧？多看几遍

package com.example.ycxh.atry;

import android.app.Fragment;
import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import static com.example.ycxh.atry.R.id.myMusicButton;

/**

• A simple {@link Fragment} subclass.
• Activities that contain this fragment must implement the
• {@link MainFragment.OnMainFragmentInteractionListener} interface
• to handle interaction events.
• Use the {@link MainFragment#newInstance} factory method to

• create an instance of this fragment.
  */
  public class MainFragment extends Fragment {
  // TODO: Rename parameter arguments, choose names that match
  // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
  private static final String ARG_PARAM1 = "param1";
  private static final String ARG_PARAM2 = "param2";

  // TODO: Rename and change types of parameters
  private String mParam1;
  private String mParam2;

  private Button but;
  private OnMainFragmentInteractionListener mListener;

  public MainFragment() {
  // Required empty public constructor
  }

  /**

  • Use this factory method to create a new instance of
  • this fragment using the provided parameters. *
  • @param param1 Parameter 1.
  • @param param2 Parameter 2.
  • @return A new instance of fragment MainFragment. */ // TODO: Rename and change types and number of parameters public static MainFragment newInstance(String param1, String param2) { MainFragment fragment = new MainFragment(); Bundle args = new Bundle(); args.putString(ARG_PARAM1, param1); args.putString(ARG_PARAM2, param2); fragment.setArguments(args); return fragment; }

  @Override
  public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  if (getArguments() != null) {
  mParam1 = getArguments().getString(ARG_PARAM1);
  mParam2 = getArguments().getString(ARG_PARAM2);
  }
  }

  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container,
  Bundle savedInstanceState) {

  View rootView = inflater.inflate(R.layout.fragment_main, container, false);
  
  but = (Button)rootView.findViewById(myMusicButton);                                                 //切换至我的音乐Fragment
          but.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
          mListener.onMainFragmentInteraction(AppConstant.PlayerMsg.CHANGE_TO_MY_MUSIC_FRAGMENT);
      }
  });
  return rootView;
  

  }

  // TODO: Rename method, update argument and hook method into UI event
  public void onButtonPressed(int message) {
  if (mListener != null) {
  mListener.onMainFragmentInteraction(message);
  }
  }

  @Override
  public void onAttach(Context context) {
  super.onAttach(context);
  if (context instanceof OnMainFragmentInteractionListener) {
  mListener = (OnMainFragmentInteractionListener) context;
  } else {
  throw new RuntimeException(context.toString()
  + " must implement OnFragmentInteractionListener");
  }
  }

  @Override
  public void onDetach() {
  super.onDetach();
  mListener = null;
  }

  /**

  • This interface must be implemented by activities that contain this
  • fragment to allow an interaction in this fragment to be communicated
  • to the activity and potentially other fragments contained in that
  • activity.
  • See the Android Training lesson <a href=
  • "http://developer.android.com/training/basics/fragments/communicating.html"

  • Communicating with Other Fragments for more information.
    */
    public interface OnMainFragmentInteractionListener {
    // TODO: Update argument type and name
    // void onFragmentInteraction(int message);

    void onMainFragmentInteraction(int message);
    }
    }