我有一個Music
類中的媒體播放器,這個類是從另一箇中學Activity
調用的。它工作正常。如何防止mediaplayer在屏幕熄滅時停止?
但是當屏幕熄滅(通過超時或按鈕)時,音樂停止播放,當回來並嘗試關閉活動時,程序進入「應用程序未響應」狀態,因爲在查詢mediaplayer.isPlaying()
處查詢IllegalStateException
。
如何防止mediaplayer在屏幕熄滅時停止?
是否需要通過服務?
假設答案是肯定的,我試圖將Music
類轉換成服務(見下文)。我還添加<service android:enabled="true" android:name=".Music" />
到Manifest.xml
,和我打電話的Music
類是這樣的:
startService(new Intent(getBaseContext(), Music.class));
Music track = Music(fileDescriptor);
只有2中的主要活動新線startService(new Intent(getBaseContext(), Music.class));
和stopService(new Intent(getBaseContext(), Music.class));
,與相應的進口在一起。
但是現在我得到InstantiationException
錯誤,因爲can't instantiate class
嘗試啓動服務時。我錯過了什麼?
這是例外:
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
,這是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();
}
}
你讀過關於如何使用服務的文檔? http://developer.android.com/reference/android/app/Service.html – deefactorial
@deefactorial當然不是!我只是想實現有史以來最基本的媒體播放器!我不希望(也不期望不需要)知道所有的細節。我只是想在這裏http://marakana.com/forums/android/examples/60.html去關注(着名的?)marakana例子。我做錯了什麼... –