java如何使媒体播放器在按设备后退按钮从片段返回活动时停止

Question

我的问题是，当我按下设备后退按钮时，媒体播放器一直在播放。当按下设备后退按钮时，如何完全销毁碎片、媒体播放器和其中的所有内容，使其在屏幕上不可见

我是编程新手，所以欢迎所有关于如何改进代码的建议和评论。多谢各位

活动：

import 安卓x.appcompat.app.AppCompatActivity;
import 安卓x.fragment.app.FragmentManager;
import 安卓.os.Bundle;
import 安卓.view.View;
import 安卓.widget.Button;

public class MainActivity extends AppCompatActivity {

    Button button1;
    Button button2;
    Button button3;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        button1 = findViewById(R.id.button1);
        button2 = findViewById(R.id.button2);
        button3 = findViewById(R.id.button3);

        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                FragmentManager fm= getSupportFragmentManager();
                fragment1 fragment = new fragment1();
                fm.beginTransaction()
                        .replace(R.id.container,fragment)
                        .addToBackStack(null)
                        .commit();
            }
        });

        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                FragmentManager fm= getSupportFragmentManager();
                fragment2 fragment= new fragment2();
                fm.beginTransaction()
                        .replace(R.id.container,fragment)
                        .addToBackStack(null)
                        .commit();
            }
        });

        button3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                FragmentManager fm= getSupportFragmentManager();
                fragment3 fragment= new fragment3();
                fm.beginTransaction()
                        .replace(R.id.container,fragment)
                        .addToBackStack(null)
                        .commit();
            }
        });
    }
}

片段：

import 安卓x.fragment.app.Fragment;
import 安卓.media.MediaPlayer;
import 安卓.view.LayoutInflater;
import 安卓.view.ViewGroup;
import 安卓.widget.Button;
import 安卓.os.Bundle;
import 安卓.widget.SeekBar;
import 安卓.os.Handler;
import 安卓.os.Message;
import 安卓.view.View;
import 安卓.widget.TextView;
import java.io.IOException;

public class fragment1 extends Fragment {

    MediaPlayer mp;
    Button play;
    SeekBar seekBar;
    TextView elapsedTimeLabel;
    TextView remainingTimeLabel;
    int totalTime;

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

        View rootView = inflater.inflate(R.layout.fragment_fragment1, container, false);

        final MediaPlayer mp = new MediaPlayer();
        try {
            mp.setDataSource("https://firebasestorage.googleapis.com...");
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            mp.prepare();
        } catch (IOException e) {
            e.printStackTrace();
        }

        final Button play = rootView.findViewById(R.id.play);
        elapsedTimeLabel = rootView.findViewById(R.id.elapsedTimeLabel);
        remainingTimeLabel = rootView.findViewById(R.id.remainingTimeLabel);
        totalTime = mp.getDuration();
        mp.seekTo(0);
        seekBar = rootView.findViewById(R.id.seekBar);
        seekBar.setMax(totalTime);
        seekBar.setOnSeekBarChangeListener

                (new SeekBar.OnSeekBarChangeListener() {
                     @Override
                     public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                         if (fromUser) {
                             mp.seekTo(progress);
                             seekBar.setProgress(progress);
                         }
                     }
                     @Override
                     public void onStartTrackingTouch(SeekBar seekBar) {
                     }
                     @Override
                     public void onStopTrackingTouch(SeekBar seekBar) {
                     }
                 }
                );

        new Thread(new Runnable() {
            @Override
            public void run() {
                while (mp != null) {
                    try {
                        Message msg = new Message();
                        msg.what = mp.getCurrentPosition();
                        handler.sendMessage(msg);
                        Thread.sleep(1000);
                    } catch (InterruptedException ignored) {
                    }
                }
            }
        }).start();

        mp.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {

            public void onCompletion(MediaPlayer sound) {

                play.setBackgroundResource(R.drawable.play);
            }
        });

        play.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (mp.isPlaying()) {
                    mp.pause();
                    play.setBackgroundResource(R.drawable.play);

                } else {

                    mp.start();
                    play.setBackgroundResource(R.drawable.pause);
                }

            }

        });

        return rootView;
    }

    private Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            int currentPosition = msg.what;
            seekBar.setProgress(currentPosition);

            String elapsedTime = createTimeLabel(currentPosition);
            elapsedTimeLabel.setText(elapsedTime);

            String remainingTime;
            remainingTime = createTimeLabel(totalTime - currentPosition);
            remainingTimeLabel.setText("-" + remainingTime);
        }
    };

    public String createTimeLabel(int time) {
        String timelabel;
        int min = time / 1000 / 60;
        int sec = time / 1000 % 60;

        timelabel = min + ":";
        if (sec < 10) timelabel += "0";
        timelabel += sec;
        return timelabel;

    }


    public void play(View view) {
        if (mp == null) {
            mp.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
                @Override
                public void onCompletion(MediaPlayer mp) {
                    stopPlayer();
                }
            });
        }

        mp.start();
    }

    public void pause(View view) {
        if (mp != null) {
            mp.pause();
        }
    }

    private void stopPlayer() {
        if (mp != null) {
            mp.release();
            mp = null;

        }
    }
}

编辑：

我尝试了提供的解决方案，但不知何故，片段中的mediaplayer没有被破坏。当我回到片段时，其中的seekbar被重置，但音频文件仍在播放。当我再次按“播放”时，它会在上一个文件的基础上再次开始播放，以便同时播放两个文件

Answer 1

@Override
public void onDestroy() {
    stopPlayer();
    super.onDestroy();
}

在Fragment中，重写OnDestroy函数。然后在调用super之前停止玩家。onDestroy（）

Answer 2

每个片段都有一个onDestroy()回调，用于在片段从后堆栈弹出并销毁时进行回调。您可以从该方法调用stopPlayer()

@Override
public void onDestroy() {
    super.onDestroy();
    stopPlayer();
}

Answer 3

不幸的是，由于片段没有onBackPressed()方法，因此没有直接的方法可以做到这一点，您必须进行回调并在片段中实现它才能使其工作

首先，您需要创建一个实现其接口的接口和类，以拥有一个泛型方法

1. 创建类接口OnBackPressedListener

打开反压侦听器。java

public interface OnBackPressedListener {
    void goBack();
}

1. 在MainActivity中，创建侦听器并为其创建一个setter，并在重写它之后在onBackPressed()方法中使用它

你的MainActivity应该是这样的

主要活动。java

public class MainActivity extends AppCompatActivity {

    private OnBackPressedListener onBackPressedListener;

    public void setOnBackPressedListener(OnBackPressedListener onBackPressedListener) {
        this.onBackPressedListener = onBackPressedListener;
    }
    
    @Override
    public void onBackPressed() {
        if (onBackPressedListener != null){
            onBackPressedListener.goBack();
        }
        super.onBackPressed();
    }
}

1. 在Fragment you should implement the OnBackPressedListener`界面中，使用它停止播放机

片段1。java

public class fragment1 extends Fragment implements OnBackPressedListener {
    
    @Override
    public void goBack() {
        stopPlayer();
    }
}

旁注

• 考虑将fragment1名称重构为Fragment1大写F