在Android问题上播放带有MediaPlayer类的mp3

我的代码出了什么问题？ 我有一个切换按钮，我想播放/停止一个MP3。 我猜代码应该如下：

package com.android.iFocus; import android.app.Activity; import android.media.MediaPlayer; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.ToggleButton; public class iFocusActivity extends Activity implements OnClickListener { public int count; MediaPlayer mediaPlayer = MediaPlayer.create(this, R.raw.rain); /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); ToggleButton toggleRain = (ToggleButton)findViewById(R.id.toggleRain); //Define Listeners toggleRain.setOnClickListener(this); count = 0; } @Override public void onClick(View toggleRain) { if(count==0){ mediaPlayer.start(); count=1; } else { //MediaPlayer mediaPlayer = MediaPlayer.create(this, R.raw.rain); mediaPlayer.pause(); mediaPlayer.stop(); mediaPlayer.release(); count=0; } } } 

问题是：Eclipse没有给出任何错误，但是在模拟器/手机上它给了我一个exception并在启动后立即死亡。 开始：

 10-02 20:28:24.312: INFO/ActivityManager(59): Starting activity: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.android.iFocus/.iFocusActivity } 10-02 20:28:24.392: DEBUG/AndroidRuntime(960): Shutting down VM 10-02 20:28:24.402: DEBUG/dalvikvm(960): Debugger has detached; object registry had 1 entries 10-02 20:28:24.462: INFO/ActivityManager(59): Start proc com.android.iFocus for activity com.android.iFocus/.iFocusActivity: pid=967 uid=10036 gids={} 10-02 20:28:24.502: INFO/AndroidRuntime(960): NOTE: attach of thread 'Binder Thread #3' failed 10-02 20:28:25.822: DEBUG/AndroidRuntime(967): Shutting down VM 10-02 20:28:25.822: WARN/dalvikvm(967): threadid=1: thread exiting with uncaught exception (group=0x4001d800) 10-02 20:28:25.932: ERROR/AndroidRuntime(967): FATAL EXCEPTION: main 10-02 20:28:25.932: ERROR/AndroidRuntime(967): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.android.iFocus/com.android.iFocus.iFocusActivity}: java.lang.NullPointerException 

好吧，当我在onClick内部类中初始化mediaPlayer时，它不会给我任何错误，并且应用程序不会给我任何启动歌曲的错误。 但它并没有停止。 所以，当我点击toggleButton时，它会启动，当我再次点击时，它没有做任何事情，只是给了我一个关于log cat的错误：

首次按切换按钮时出错并且歌曲开始正常（但是会出现此错误）：

 10-02 20:39:02.712: INFO/ActivityManager(59): Start proc com.android.iFocus for activity com.android.iFocus/.iFocusActivity: pid=996 uid=10036 gids={} 10-02 20:39:02.782: INFO/AndroidRuntime(989): NOTE: attach of thread 'Binder Thread #3' failed 10-02 20:39:04.432: INFO/ActivityManager(59): Displayed activity com.android.iFocus/.iFocusActivity: 1804 ms (total 640049 ms) 10-02 20:39:08.672: DEBUG/AudioSink(34): bufferCount (4) is too small and increased to 12 10-02 20:39:08.982: WARN/AudioFlinger(34): write blocked for 73 msecs, 2105 delayed writes, thread 0xb3b8 10-02 20:39:09.682: DEBUG/dalvikvm(437): GC_EXPLICIT freed 686 objects / 38192 bytes in 216ms 10-02 20:39:14.502: WARN/AudioFlinger(34): write blocked for 86 msecs, 2110 delayed writes, thread 0xb3b8 10-02 20:39:14.642: DEBUG/dalvikvm(188): GC_EXPLICIT freed 164 objects / 11408 bytes in 176ms 10-02 20:39:19.622: DEBUG/dalvikvm(261): GC_EXPLICIT freed 43 objects / 1912 bytes in 154ms 10-02 20:39:20.352: WARN/AudioFlinger(34): write blocked for 78 msecs, 2119 delayed writes, thread 0xb3b8 

当我再次按下toggleButton并且歌曲应该停止时出错：

 10-02 20:43:22.412: ERROR/MediaPlayer(1032): pause called in state 8 10-02 20:43:22.412: ERROR/MediaPlayer(1032): error (-38, 0) 10-02 20:43:22.412: ERROR/MediaPlayer(1032): stop called in state 0 10-02 20:43:22.412: ERROR/MediaPlayer(1032): error (-38, 0) 10-02 20:43:22.612: WARN/MediaPlayer(1032): mediaplayer went away with unhandled events 10-02 20:43:22.612: WARN/MediaPlayer(1032): mediaplayer went away with unhandled events 10-02 20:43:22.622: WARN/MediaPlayer(1032): mediaplayer went away with unhandled events 10-02 20:43:22.622: WARN/MediaPlayer(1032): mediaplayer went away with unhandled events 

Answer 1

首先，我的分析：1。你没有在onCreate（）中初始化MediaPlayer：

 MediaPlayer mediaPlayer = MediaPlayer.create(this, R.raw.rain); 

‘this’<---这个东西是NULL，所以你在运行时有一个NullPointerException，首先加载应用程序时间。
2.在第二次点击按钮时，你已经打过电话

 mediaPlayer.release(); 

下次单击MediaPlayer State时的exception

好吧，修复非常简单，你需要考虑Android编程的最佳实践：

 package pete.android.study; import android.app.Activity; import android.media.MediaPlayer; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.ToggleButton; public class Main extends Activity implements OnClickListener { // declare controls public int count = 0; MediaPlayer mediaPlayer = null; ToggleButton toggleRain = null; /* * (non-Javadoc) * @see android.app.Activity#onCreate(android.os.Bundle) */ @Override public void onCreate(Bundle savedInstanceState) { // load layout super.onCreate(savedInstanceState); setContentView(R.layout.main); // load controls toggleRain = (ToggleButton)findViewById(R.id.toggleRain); // init player mediaPlayer = MediaPlayer.create(this, R.raw.rain); // set click event handler toggleRain.setOnClickListener(this); // init state for playing count = 0; } /* * (non-Javadoc) * @see android.view.View.OnClickListener#onClick(android.view.View) */ @Override public void onClick(View toggleRain) { if(count == 0){ mediaPlayer.start(); count = 1; } else { mediaPlayer.pause(); count = 0; } } /* * (non-Javadoc) * @see android.app.Activity#onDestroy() */ @Override protected void onDestroy() { if(mediaPlayer != null) { mediaPlayer.stop(); mediaPlayer.release(); mediaPlayer = null; } } } 

当然它像魅力^^一样工作！ 有很多方法可以改进这个简单的应用程序，但是，我猜您可以通过查看Android开发人员的参考文档来查找:)

Answer 2

您是否尝试过在onCreate内部而不是仅仅在类体内部进行初始化？ 这将是最好的地方。

如果在onClick内部初始化，则会显示您显示的错误。 这是因为每次单击时都会创建一个新的MediaPlayer实例。

Answer 3

你的问题在于release()声明：

 if(count==0){ mediaPlayer.start(); count = 1; } else { //MediaPlayer mediaPlayer = MediaPlayer.create(this, R.raw.rain); mediaPlayer.pause(); mediaPlayer.stop(); mediaPlayer.release(); count = 0; } 

根据您的预期结果，您可以通过几种不同的方式对其进行更改。 如果您只是想播放/暂停，正如您所说，那么您只需要删除stop()和release()调用。 特别release() 。 该调用将音频资源释放回系统，这意味着您需要先将其恢复到准备状态，然后才能再次使用它。

我强烈建议非常彻底地阅读此参考文档 。 MediaPlayer类相当复杂，当状态管理不当时，这样的错误就很容易出现。