当您在未单击播放的情况下按暂停或停止时,Android 广播流媒体应用程序崩溃
当我启动我的应用程序并按停止或暂停时,Android 应用程序将崩溃。如果您先按播放然后停止或暂停,效果很好。我在 google 和 stackoverflow 上搜索过,但找不到太多相关信息。我认为问题是因为 NullPointerException 但由于我也是 java 新手,它并没有告诉我太多有关问题的信息
代码:
import android.app.Activity;
import android.media.AudioManager;
import android.media.MediaPlayer;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class myMain extends Activity implements
MediaPlayer.OnCompletionListener, MediaPlayer.OnPreparedListener,
MediaPlayer.OnErrorListener, MediaPlayer.OnBufferingUpdateListener, OnClickListener {
private String TAG = getClass().getSimpleName();
private MediaPlayer mp= null;
private Button play;
private Button pause;
private Button stop;
@Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
setContentView(R.layout.main);
play = (Button) findViewById(R.id.play);
pause = (Button) findViewById(R.id.pause);
stop = (Button) findViewById(R.id.stop);
play.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
play();
}
});
pause.setOnClickListener(new View.OnClickListener() {
public void onClick(View view){
pause();
}
});
stop.setOnClickListener(new View.OnClickListener() {
public void onClick(View view){
stop();
}
});
}
private void play() {
Uri myUri = Uri.parse("url");
try {
if (mp == null) {
this.mp = new MediaPlayer();
} else {
mp.stop();
mp.reset();
}
mp.setDataSource(this, myUri); // Go to Initialized state
mp.setAudioStreamType(AudioManager.STREAM_MUSIC);
mp.setOnPreparedListener(this);
mp.setOnBufferingUpdateListener(this);
mp.setOnErrorListener(this);
mp.prepareAsync();
Log.d(TAG, "LoadClip Done");
} catch (Throwable t) {
Log.d(TAG, t.toString());
}
}
public void onPrepared(MediaPlayer mp) {
Log.d(TAG, "Stream is prepared");
mp.start();
}
private void pause() {
mp.pause();
}
private void stop() {
mp.stop();
}
@Override
public void onDestroy() {
super.onDestroy();
stop();
}
public void onCompletion(MediaPlayer mp) {
stop();
}
public boolean onError(MediaPlayer mp, int what, int extra) {
StringBuilder sb = new StringBuilder();
sb.append("Media Player Error: ");
switch (what) {
case MediaPlayer.MEDIA_ERROR_NOT_VALID_FOR_PROGRESSIVE_PLAYBACK:
sb.append("Not Valid for Progressive Playback");
break;
case MediaPlayer.MEDIA_ERROR_SERVER_DIED:
sb.append("Server Died");
break;
case MediaPlayer.MEDIA_ERROR_UNKNOWN:
sb.append("Unknown");
break;
default:
sb.append(" Non standard (");
sb.append(what);
sb.append(")");
}
sb.append(" (" + what + ") ");
sb.append(extra);
Log.e(TAG, sb.toString());
return true;
}
public void onBufferingUpdate(MediaPlayer mp, int percent) {
Log.d(TAG, "PlayerService onBufferingUpdate : " + percent + "%");
}
public void onClick(View v) {
// TODO Auto-generated method stub
}
}
错误:
02-11 20:45:43.837: D/AndroidRuntime(338): Shutting down VM
02-11 20:45:43.837: W/dalvikvm(338): threadid=1: thread exiting with uncaught exception (group=0x40015560)
02-11 20:45:43.857: E/AndroidRuntime(338): FATAL EXCEPTION: main
02-11 20:45:43.857: E/AndroidRuntime(338): java.lang.NullPointerException
02-11 20:45:43.857: E/AndroidRuntime(338): at wadio.media.internetradio.myMain.stop(myMain.java:95)
02-11 20:45:43.857: E/AndroidRuntime(338): at wadio.media.internetradio.myMain.access$2(myMain.java:94)
02-11 20:45:43.857: E/AndroidRuntime(338): at wadio.media.internetradio.myMain$3.onClick(myMain.java:55)
02-11 20:45:43.857: E/AndroidRuntime(338): at android.view.View.performClick(View.java:2485)
02-11 20:45:43.857: E/AndroidRuntime(338): at android.view.View$PerformClick.run(View.java:9080)
02-11 20:45:43.857: E/AndroidRuntime(338): at android.os.Handler.handleCallback(Handler.java:587)
02-11 20:45:43.857: E/AndroidRuntime(338): at android.os.Handler.dispatchMessage(Handler.java:92)
02-11 20:45:43.857: E/AndroidRuntime(338): at android.os.Looper.loop(Looper.java:123)
02-11 20:45:43.857: E/AndroidRuntime(338): at android.app.ActivityThread.main(ActivityThread.java:3683)
02-11 20:45:43.857: E/AndroidRuntime(338): at java.lang.reflect.Method.invokeNative(Native Method)
02-11 20:45:43.857: E/AndroidRuntime(338): at java.lang.reflect.Method.invoke(Method.java:507)
02-11 20:45:43.857: E/AndroidRuntime(338): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
02-11 20:45:43.857: E/AndroidRuntime(338): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
02-11 20:45:43.857: E/AndroidRuntime(338): at dalvik.system.NativeStart.main(Native Method)
When i start my app and press stop or pause the android app will crash. It works fine if you press play first and then stop or pause. I searched on google and stackoverflow but i couldn't find much about it. I think the problem is because of a NullPointerException but since i'm new too java it doesn't tell me much about the problem
The code:
import android.app.Activity;
import android.media.AudioManager;
import android.media.MediaPlayer;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class myMain extends Activity implements
MediaPlayer.OnCompletionListener, MediaPlayer.OnPreparedListener,
MediaPlayer.OnErrorListener, MediaPlayer.OnBufferingUpdateListener, OnClickListener {
private String TAG = getClass().getSimpleName();
private MediaPlayer mp= null;
private Button play;
private Button pause;
private Button stop;
@Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
setContentView(R.layout.main);
play = (Button) findViewById(R.id.play);
pause = (Button) findViewById(R.id.pause);
stop = (Button) findViewById(R.id.stop);
play.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
play();
}
});
pause.setOnClickListener(new View.OnClickListener() {
public void onClick(View view){
pause();
}
});
stop.setOnClickListener(new View.OnClickListener() {
public void onClick(View view){
stop();
}
});
}
private void play() {
Uri myUri = Uri.parse("url");
try {
if (mp == null) {
this.mp = new MediaPlayer();
} else {
mp.stop();
mp.reset();
}
mp.setDataSource(this, myUri); // Go to Initialized state
mp.setAudioStreamType(AudioManager.STREAM_MUSIC);
mp.setOnPreparedListener(this);
mp.setOnBufferingUpdateListener(this);
mp.setOnErrorListener(this);
mp.prepareAsync();
Log.d(TAG, "LoadClip Done");
} catch (Throwable t) {
Log.d(TAG, t.toString());
}
}
public void onPrepared(MediaPlayer mp) {
Log.d(TAG, "Stream is prepared");
mp.start();
}
private void pause() {
mp.pause();
}
private void stop() {
mp.stop();
}
@Override
public void onDestroy() {
super.onDestroy();
stop();
}
public void onCompletion(MediaPlayer mp) {
stop();
}
public boolean onError(MediaPlayer mp, int what, int extra) {
StringBuilder sb = new StringBuilder();
sb.append("Media Player Error: ");
switch (what) {
case MediaPlayer.MEDIA_ERROR_NOT_VALID_FOR_PROGRESSIVE_PLAYBACK:
sb.append("Not Valid for Progressive Playback");
break;
case MediaPlayer.MEDIA_ERROR_SERVER_DIED:
sb.append("Server Died");
break;
case MediaPlayer.MEDIA_ERROR_UNKNOWN:
sb.append("Unknown");
break;
default:
sb.append(" Non standard (");
sb.append(what);
sb.append(")");
}
sb.append(" (" + what + ") ");
sb.append(extra);
Log.e(TAG, sb.toString());
return true;
}
public void onBufferingUpdate(MediaPlayer mp, int percent) {
Log.d(TAG, "PlayerService onBufferingUpdate : " + percent + "%");
}
public void onClick(View v) {
// TODO Auto-generated method stub
}
}
The errors:
02-11 20:45:43.837: D/AndroidRuntime(338): Shutting down VM
02-11 20:45:43.837: W/dalvikvm(338): threadid=1: thread exiting with uncaught exception (group=0x40015560)
02-11 20:45:43.857: E/AndroidRuntime(338): FATAL EXCEPTION: main
02-11 20:45:43.857: E/AndroidRuntime(338): java.lang.NullPointerException
02-11 20:45:43.857: E/AndroidRuntime(338): at wadio.media.internetradio.myMain.stop(myMain.java:95)
02-11 20:45:43.857: E/AndroidRuntime(338): at wadio.media.internetradio.myMain.access$2(myMain.java:94)
02-11 20:45:43.857: E/AndroidRuntime(338): at wadio.media.internetradio.myMain$3.onClick(myMain.java:55)
02-11 20:45:43.857: E/AndroidRuntime(338): at android.view.View.performClick(View.java:2485)
02-11 20:45:43.857: E/AndroidRuntime(338): at android.view.View$PerformClick.run(View.java:9080)
02-11 20:45:43.857: E/AndroidRuntime(338): at android.os.Handler.handleCallback(Handler.java:587)
02-11 20:45:43.857: E/AndroidRuntime(338): at android.os.Handler.dispatchMessage(Handler.java:92)
02-11 20:45:43.857: E/AndroidRuntime(338): at android.os.Looper.loop(Looper.java:123)
02-11 20:45:43.857: E/AndroidRuntime(338): at android.app.ActivityThread.main(ActivityThread.java:3683)
02-11 20:45:43.857: E/AndroidRuntime(338): at java.lang.reflect.Method.invokeNative(Native Method)
02-11 20:45:43.857: E/AndroidRuntime(338): at java.lang.reflect.Method.invoke(Method.java:507)
02-11 20:45:43.857: E/AndroidRuntime(338): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
02-11 20:45:43.857: E/AndroidRuntime(338): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
02-11 20:45:43.857: E/AndroidRuntime(338): at dalvik.system.NativeStart.main(Native Method)
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在您的
stop()
方法中,您访问mp
变量。但是,在您按下播放键(并且调用play()
方法)之前,mp
变量为 null。因此,当您尝试访问 null 变量时,会引发 NullPointerException。停止 NullPointerException 的一个非常简单的方法是执行以下操作:
当然,此解决方案不考虑调用两次暂停或停止的情况。查看
MediaPlayer
文档有关状态管理的更多信息。In your
stop()
method you access themp
variable. However, themp
variable is null until you press play (and theplay()
method is called). So when you try to access the null variable a NullPointerException is thrown.A very simple way to stop the NullPointerException is to do something like this:
Of course this solution doesn't account for cases where pause or stop is called twice. Take a look at the
MediaPlayer
documentation for more info on state management.