android - fragment 中的多个音频

Question

完全是菜鸟，看不懂这个问题。一个应用程序有一个 Activity ，两个 fragment ，每个 fragment 包含 15 行，每行有两个 TextView 和一个按钮(用于播放音频 fragment )。启动成功，我注意到，如果我不播放音频，它工作正常，我可以导航到任何地方，任何 fragment ，或者轻松地来回导航到 Activity ，但如果我播放音频，然后尝试移动到另一个 fragment 或 Activity ，应用程序崩溃。开始时启动的 Activity 仅带有两个 Button 以导航到 fragment 。这个应用程序有什么问题？我只添加了第一个 fragment 和一些行..请建议..

  package com.misty.multiaudioexperiments;
    import android.os.Bundle;
    import androidx.annotation.NonNull;
    import androidx.annotation.Nullable;
    import androidx.fragment.app.Fragment;
    import androidx.fragment.app.FragmentTransaction;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.content.Intent;
    import android.media.MediaPlayer;
    import android.widget.Button;



    public class FragmentOne extends Fragment {
        MediaPlayer mp = new MediaPlayer();

        @Nullable
        @Override
        public View onCreateView(@NonNull final LayoutInflater inflater, @Nullable final ViewGroup container, @Nullable Bundle savedInstanceState) {
            //return super.onCreateView(inflater, container, savedInstanceState);

            View view = inflater.inflate(R.layout.fragment_fragment_one, container, false);




            final Button buttonInFragmentOneToPlayAudioMenInEnglishVar = (Button)view.findViewById(R.id.buttonInFragmentOneToPlayAudioMenInEnglishId);
            final Button buttonInFragmentOneToPlayAudioPencilInEnglishVar = (Button)view.findViewById(R.id.buttonInFragmentOneToPlayAudioPencilInEnglishId);
            final Button buttonInFragmentOneToPlayAudioPilotInEnglishVar = (Button)view.findViewById(R.id.buttonInFragmentOneToPlayAudioPilotInEnglishId);
            final Button buttonInFragmentOneToPlayAudioRunInEnglishVar = (Button)view.findViewById(R.id.buttonInFragmentOneToPlayAudioRunInEnglishId);
            final Button buttonInFragmentOneToPlayAudioShoeInEnglishVar = (Button)view.findViewById(R.id.buttonInFragmentOneToPlayAudioShoeInEnglishId);



            final Button buttonInFragmentOneForTransitionToContentsVar = (Button)view.findViewById(R.id.buttonInFragmentOneForTransitionToContentsId);
            final Button buttonInFragmentOneForTransitionToNextFragmentVar = (Button)view.findViewById(R.id.buttonInFragmentOneForTransitionToNextFragmentId);





        buttonInFragmentOneToPlayAudioMenInEnglishVar.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


                if(mp != null) {
                    if(mp.isPlaying()){
                        mp.stop();
                        mp.release();
                    }
                }

                mp = MediaPlayer.create(getActivity().getApplicationContext(), R.raw.men);
                mp.start();
                mp.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
                    public void onCompletion(MediaPlayer mediaPlayer) {
                        mp.release();
                        mp = null;




                    }
                });



            }
        });


















        buttonInFragmentOneToPlayAudioPencilInEnglishVar.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


                if(mp != null) {
                    if(mp.isPlaying()){
                        mp.stop();
                        mp.release();
                    }
                }

                mp = MediaPlayer.create(getActivity().getApplicationContext(), R.raw.pencil);
                mp.start();
                mp.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
                    public void onCompletion(MediaPlayer mediaPlayer) {
                        mp.release();
                        mp = null;




                    }
                });



            }
        });
















        buttonInFragmentOneToPlayAudioPilotInEnglishVar.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


                if(mp != null) {
                    if(mp.isPlaying()){
                        mp.stop();
                        mp.release();
                    }
                }

                mp = MediaPlayer.create(getActivity().getApplicationContext(), R.raw.pilot);
                mp.start();
                mp.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
                    public void onCompletion(MediaPlayer mediaPlayer) {
                        mp.release();
                        mp = null;




                    }
                });



            }
        });















        buttonInFragmentOneToPlayAudioRunInEnglishVar.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


                if(mp != null) {
                    if(mp.isPlaying()){
                        mp.stop();
                        mp.release();
                    }
                }

                mp = MediaPlayer.create(getActivity().getApplicationContext(), R.raw.run);
                mp.start();
                mp.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
                    public void onCompletion(MediaPlayer mediaPlayer) {
                        mp.release();
                        mp = null;




                    }
                });



            }
        });



















        buttonInFragmentOneToPlayAudioShoeInEnglishVar.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


                if(mp != null) {
                    if(mp.isPlaying()){
                        mp.stop();
                        mp.release();
                    }
                }

                mp = MediaPlayer.create(getActivity().getApplicationContext(), R.raw.shoe);
                mp.start();
                mp.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
                    public void onCompletion(MediaPlayer mediaPlayer) {
                        mp.release();
                        mp = null;




                    }
                });



            }
        });

















        buttonInFragmentOneForTransitionToContentsVar.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Intent intent1 = new Intent(getActivity(), MainActivity.class);
                startActivity(intent1);
                mp.reset();
                mp.release();
                mp = null;

            }
        });




//THIS BUTTON TAKES TO THE NEXT OR FRAGMENT TWO PAGE STOPPING MEDIAPLAYER IF PLAYING

        buttonInFragmentOneForTransitionToNextFragmentVar.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                FragmentTransaction ft = getFragmentManager().beginTransaction();
                ft.replace(R.id.fragmentContainer, new FragmentTwo());
                ft.commit();
                mp.reset();
                mp.release();
                mp = null;



            }
        });



        return view;
    }
}

Answer 1

您收到异常是因为当您尝试退出 fragment 时 mp 实例为空。

1. 在创建 fragment 的新实例时实例化 mp 引用

public class FragmentOne extends Fragment {
    MediaPlayer mp = new MediaPlayer();

1. 每次播放音频时 mp 引用都会失效

mp.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
    public void onCompletion(MediaPlayer mediaPlayer) {
         mp.release();
         mp = null;
    }
});

案例 1:

如果您离开 fragment 而不播放任何音频，则实例不会被更改，因此您不会得到任何异常。

案例 2:

如果您在播放一些音频后离开 fragment ，mp 实例将设置为 null，因此当您尝试在 null 实例上调用 mp.reset() 时，会导致异常。

解决方案

用 if block 包围退出检查:-

if(mp != null){
     mp.reset();
     mp.release();
     mp = null;
}

作为最佳实践，在两个 fragment 的 onStop() 方法中执行此检查，并将其从 onClick()

中删除

    @Override
    public void onStop() {
        if(mp != null){
            mp.reset();
            mp.release();
            mp = null;
        }
        super.onStop();
    }

希望对你有帮助