我有一个媒体播放器在一个名为
但是当屏幕关闭(无论是超时还是按按钮)时,音乐停止播放,当回到并尝试关闭活动时,程序会进入“应用程序未响应”状态,因为查询时出现了
如何防止媒体播放器在屏幕关闭时停止播放?
它必须通过服务来完成吗?
假设答案是肯定的,我尝试将
在主 Activity 中,唯一新增的两行代码是
但现在我在尝试启动服务时遇到了
以下是异常信息:
Music
的类中,该类从另一个次要的Activity
中调用。它工作得很好。但是当屏幕关闭(无论是超时还是按按钮)时,音乐停止播放,当回到并尝试关闭活动时,程序会进入“应用程序未响应”状态,因为查询时出现了
IllegalStateException
,如mediaplayer.isPlaying()
。如何防止媒体播放器在屏幕关闭时停止播放?
它必须通过服务来完成吗?
假设答案是肯定的,我尝试将
Music
类转换为服务(见下文)。我还将<service android:enabled="true" android:name=".Music" />
添加到Manifest.xml
中,并像这样调用Music
类:startService(new Intent(getBaseContext(), Music.class));
Music track = Music(fileDescriptor);
在主 Activity 中,唯一新增的两行代码是
startService(new Intent(getBaseContext(), Music.class));
和 stopService(new Intent(getBaseContext(), Music.class));
,以及相应的导入。但现在我在尝试启动服务时遇到了
InstantiationException
错误,因为无法实例化类。我漏掉了什么?以下是异常信息:
E/AndroidRuntime(16642): FATAL EXCEPTION: main
E/AndroidRuntime(16642): java.lang.RuntimeException: Unable to instantiate service com.floritfoto.apps.ave.Music: java.lang.InstantiationException: can't instantiate class com.floritfoto.apps.ave.Music; no empty constructor
E/AndroidRuntime(16642): at android.app.ActivityThread.handleCreateService(ActivityThread.java:2249)
E/AndroidRuntime(16642): at android.app.ActivityThread.access$1600(ActivityThread.java:127)
E/AndroidRuntime(16642): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1213)
E/AndroidRuntime(16642): at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime(16642): at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime(16642): at android.app.ActivityThread.main(ActivityThread.java:4507)
E/AndroidRuntime(16642): at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(16642): at java.lang.reflect.Method.invoke(Method.java:511)
E/AndroidRuntime(16642): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:980)
E/AndroidRuntime(16642): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:747)
E/AndroidRuntime(16642): at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime(16642): Caused by: java.lang.InstantiationException: can't instantiate class com.floritfoto.apps.ave.Music; no empty constructor
E/AndroidRuntime(16642): at java.lang.Class.newInstanceImpl(Native Method)
E/AndroidRuntime(16642): at java.lang.Class.newInstance(Class.java:1319)
E/AndroidRuntime(16642): at android.app.ActivityThread.handleCreateService(ActivityThread.java:2246)
E/AndroidRuntime(16642): ... 10 more
这是Music.class:
package com.floritfoto.apps.ave;
import java.io.FileDescriptor;
import java.io.IOException;
import android.app.Service;
import android.content.Intent;
import android.media.MediaPlayer;
import android.media.MediaPlayer.OnCompletionListener;
import android.os.IBinder;
import android.widget.Toast;
public class Music extends Service implements OnCompletionListener{
MediaPlayer mediaPlayer;
boolean isPrepared = false;
//// TEstes de servico
@Override
public void onCreate() {
super.onCreate();
info("Servico criado!");
}
@Override
public void onDestroy() {
info("Servico fudeu!");
}
@Override
public void onStart(Intent intent, int startid) {
info("Servico started!");
}
@Override
public IBinder onBind(Intent intent) {
return null;
}
public void info(String txt) {
Toast toast = Toast.makeText(getApplicationContext(), txt, Toast.LENGTH_LONG);
toast.show();
}
//// Fim testes de servico
public Music(FileDescriptor fileDescriptor){
mediaPlayer = new MediaPlayer();
try{
mediaPlayer.setDataSource(fileDescriptor);
mediaPlayer.prepare();
isPrepared = true;
mediaPlayer.setOnCompletionListener(this);
} catch(Exception ex){
throw new RuntimeException("Couldn't load music, uh oh!");
}
}
public void onCompletion(MediaPlayer mediaPlayer) {
synchronized(this){
isPrepared = false;
}
}
public void play() {
if(mediaPlayer.isPlaying()) return;
try{
synchronized(this){
if(!isPrepared){
mediaPlayer.prepare();
}
mediaPlayer.seekTo(0);
mediaPlayer.start();
}
} catch(IllegalStateException ex){
ex.printStackTrace();
} catch(IOException ex){
ex.printStackTrace();
}
}
public void stop() {
mediaPlayer.stop();
synchronized(this){
isPrepared = false;
}
}
public void switchTracks(){
mediaPlayer.seekTo(0);
mediaPlayer.pause();
}
public void pause() {
mediaPlayer.pause();
}
public boolean isPlaying() {
return mediaPlayer.isPlaying();
}
public boolean isLooping() {
return mediaPlayer.isLooping();
}
public void setLooping(boolean isLooping) {
mediaPlayer.setLooping(isLooping);
}
public void setVolume(float volumeLeft, float volumeRight) {
mediaPlayer.setVolume(volumeLeft, volumeRight);
}
public String getDuration() {
return String.valueOf((int)(mediaPlayer.getDuration()/1000));
}
public void dispose() {
if(mediaPlayer.isPlaying()){
stop();
}
mediaPlayer.release();
}
}