android实现背景音乐播放功能

参考了一下网上别人写的，再使用的时候是放在新开的线程中来播放音乐的，后来发现每次进入Activity后就会重复开始一个音乐播放的声音。为了避免重复开启播放功能我在原来代码的基础上增加了单例模式。这样就避免了出现重复播放。

package com.liu.zhen.utils; 

import android.content.Context;
import android.content.res.AssetFileDescriptor;
import android.media.MediaPlayer;
import android.util.Log; 

/**
 *
 * This class is used for controlling background music
 *
 */
public class BackgroundMusic {
  private static BackgroundMusic backgroundMusic = null;
  private static final String TAG = "Bg_Music";
  private float mLeftVolume;
  private float mRightVolume;
  private Context mContext;
  private MediaPlayer mBackgroundMediaPlayer;
  private boolean mIsPaused;
  private String mCurrentPath; 

  private BackgroundMusic(Context context) {
    this.mContext = context;
    initData();
  } 

  public static BackgroundMusic getInstance(Context context) {
    if (backgroundMusic == null) {
      backgroundMusic = new BackgroundMusic(context);
    }
    return backgroundMusic;
  } 

  // 初始化一些数据
  private void initData() {
    mLeftVolume = 0.5f;
    mRightVolume = 0.5f;
    mBackgroundMediaPlayer = null;
    mIsPaused = false;
    mCurrentPath = null;
  } 

  /**
   * 根据path路径播放背景音乐
   *
   * @param path
   *      :assets中的音频路径
   * @param isLoop
   *      :是否循环播放
   */
  public void playBackgroundMusic(String path, boolean isLoop) {
    if (mCurrentPath == null) {
      // 这是第一次播放背景音乐--- it is the first time to play background music
      // 或者是执行end()方法后，重新被叫---or end() was called
      mBackgroundMediaPlayer = createMediaplayerFromAssets(path);
      mCurrentPath = path;
    } else {
      if (!mCurrentPath.equals(path)) {
        // 播放一个新的背景音乐--- play new background music
        // 释放旧的资源并生成一个新的----release old resource and create a new one
        if (mBackgroundMediaPlayer != null) {
          mBackgroundMediaPlayer.release();
        }
        mBackgroundMediaPlayer = createMediaplayerFromAssets(path);
        // 记录这个路径---record the path
        mCurrentPath = path;
      }
    } 

    if (mBackgroundMediaPlayer == null) {
      Log.e(TAG, "playBackgroundMusic: background media player is null");
    } else {
      // 若果音乐正在播放或已近中断，停止它---if the music is playing or paused, stop it
      mBackgroundMediaPlayer.stop();
      mBackgroundMediaPlayer.setLooping(isLoop);
      try {
        mBackgroundMediaPlayer.prepare();
        mBackgroundMediaPlayer.seekTo(0);
        mBackgroundMediaPlayer.start();
        this.mIsPaused = false;
      } catch (Exception e) {
        Log.e(TAG, "playBackgroundMusic: error state");
      }
    }
  } 

  /**
   * 停止播放背景音乐
   */
  public void stopBackgroundMusic() {
    if (mBackgroundMediaPlayer != null) {
      mBackgroundMediaPlayer.stop();
      // should set the state, if not , the following sequence will be
      // error
      // play -> pause -> stop -> resume
      this.mIsPaused = false;
    }
  } 

  /**
   * 暂停播放背景音乐
   */
  public void pauseBackgroundMusic() {
    if (mBackgroundMediaPlayer != null
        && mBackgroundMediaPlayer.isPlaying()) {
      mBackgroundMediaPlayer.pause();
      this.mIsPaused = true;
    }
  } 

  /**
   * 继续播放背景音乐
   */
  public void resumeBackgroundMusic() {
    if (mBackgroundMediaPlayer != null && this.mIsPaused) {
      mBackgroundMediaPlayer.start();
      this.mIsPaused = false;
    }
  } 

  /**
   * 重新播放背景音乐
   */
  public void rewindBackgroundMusic() {
    if (mBackgroundMediaPlayer != null) {
      mBackgroundMediaPlayer.stop();
      try {
        mBackgroundMediaPlayer.prepare();
        mBackgroundMediaPlayer.seekTo(0);
        mBackgroundMediaPlayer.start();
        this.mIsPaused = false;
      } catch (Exception e) {
        Log.e(TAG, "rewindBackgroundMusic: error state");
      }
    }
  } 

  /**
   * 判断背景音乐是否正在播放
   *
   * @return：返回的boolean值代表是否正在播放
   */
  public boolean isBackgroundMusicPlaying() {
    boolean ret = false;
    if (mBackgroundMediaPlayer == null) {
      ret = false;
    } else {
      ret = mBackgroundMediaPlayer.isPlaying();
    }
    return ret;
  } 

  /**
   * 结束背景音乐，并释放资源
   */
  public void end() {
    if (mBackgroundMediaPlayer != null) {
      mBackgroundMediaPlayer.release();
    }
    // 重新“初始化数据”
    initData();
  } 

  /**
   * 得到背景音乐的“音量”
   *
   * @return
   */
  public float getBackgroundVolume() {
    if (this.mBackgroundMediaPlayer != null) {
      return (this.mLeftVolume + this.mRightVolume) / 2;
    } else {
      return 0.0f;
    }
  } 

  /**
   * 设置背景音乐的音量
   *
   * @param volume
   *      ：设置播放的音量，float类型
   */
  public void setBackgroundVolume(float volume) {
    this.mLeftVolume = this.mRightVolume = volume;
    if (this.mBackgroundMediaPlayer != null) {
      this.mBackgroundMediaPlayer.setVolume(this.mLeftVolume,
          this.mRightVolume);
    }
  } 

  /**
   * create mediaplayer for music
   *
   * @param path
   *      the path relative to assets
   * @return
   */
  private MediaPlayer createMediaplayerFromAssets(String path) {
    MediaPlayer mediaPlayer = null;
    try {
      AssetFileDescriptor assetFileDescritor = mContext.getAssets()
          .openFd(path);
      mediaPlayer = new MediaPlayer();
      mediaPlayer.setDataSource(assetFileDescritor.getFileDescriptor(),
          assetFileDescritor.getStartOffset(),
          assetFileDescritor.getLength());
      mediaPlayer.prepare();
      mediaPlayer.setVolume(mLeftVolume, mRightVolume);
    } catch (Exception e) {
      mediaPlayer = null;
      Log.e(TAG, "error: " + e.getMessage(), e);
    }
    return mediaPlayer;
  }
} 

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