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异常并在启动后立即死亡。在这里：
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，只是给我一个关于log cat的错误：
首次按下切换按钮并且歌曲开始正常时出错（但是出现此错误）：
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并且歌曲应停止时出现错误：
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
答案 0 :(得分：4)
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'＆lt; ---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。在第二次单击按钮时，您已调用
mediaPlayer.release();
下次点击MediaPlayer State
时出现异常嗯，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;
}
}
}
当然它的功能就像魅力^^！ 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了解：）
答案 1 :(得分：0)
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。
答案 2 :(得分：0)
您的问题在于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。如果你只是想播放/暂停，就像你说的那样，那么你只需要删除stop()和release()来电。特别是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。
我强烈建议您彻底阅读this reference document。 MediaPlayer类相当复杂，当状态管理不当时，这样的错误很容易出现。