android實現背景音樂播放

參考了一下網上比人寫的，再使用的時候是放在新開的線程中來播放音樂的，後來發現每次進入Activity後就會重復開始一個音樂播放的聲音。為了避免重復開啟播放功能我在原來代碼的基礎上增加了單例模式。這樣就避免了出現重復播放。

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;
	}

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

	/**
	 * 根據path路徑播放背景音樂
	 * 
	 * @param path
	 *            :assets中的音頻路徑
	 * @param isLoop
	 *            :是否循環播放
	 */
	public void playBackgroundMusic(String path, boolean isLoop) {
		if (mCurrentPath == null) {
			// 這是第一次播放背景音樂--- it is the first time to play background music
			// 或者是執行end()方法後，重新被叫---or end() was called
			mBackgroundMediaPlayer = createMediaplayerFromAssets(path);
			mCurrentPath = path;
		} else {
			if (!mCurrentPath.equals(path)) {
				// 播放一個新的背景音樂--- play new background music
				// 釋放舊的資源並生成一個新的----release old resource and create a new one
				if (mBackgroundMediaPlayer != null) {
					mBackgroundMediaPlayer.release();
				}
				mBackgroundMediaPlayer = createMediaplayerFromAssets(path);
				// 記錄這個路徑---record the path
				mCurrentPath = path;
			}
		}

		if (mBackgroundMediaPlayer == null) {
			Log.e(TAG, "playBackgroundMusic: background media player is null");
		} else {
			// 若果音樂正在播放或已近中斷，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");
			}
		}
	}

	/**
	 * 停止播放背景音樂
	 */
	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;
		}
	}

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

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

	/**
	 * 重新播放背景音樂
	 */
	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");
			}
		}
	}

	/**
	 * 判斷背景音樂是否正在播放
	 * 
	 * @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;
	}

	/**
	 * 結束背景音樂，並釋放資源
	 */
	public void end() {
		if (mBackgroundMediaPlayer != null) {
			mBackgroundMediaPlayer.release();
		}
		// 重新“初始化數據”
		initData();
	}

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

	/**
	 * 設置背景音樂的音量
	 * 
	 * @param volume
	 *            ：設置播放的音量，float類型
	 */
	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;
	}
}