问题
I am making a media player which plays music using an URL. I implemented a foreground service and also a notification. They are working fine. The problem is when I implement .stop function in media player , which is (rathu.stop)in my code, Apps gives an error displaying app stops working. I understand that I have used stop media player function in onDestroy method of service, but I dont know other place to implement that function. Then I have to set that method to a Onclicklistner also. Please help me.
Following are my codes.
MainActivity.java
package com.example.yomal.rathumakarafm;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.content.Context;
import android.content.Intent;
import android.media.AudioManager;
import android.media.MediaPlayer;
import android.os.Build;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Gravity;
import android.view.KeyEvent;
import android.view.View;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.SeekBar;
import android.widget.Toast;
import java.io.IOException;
import java.security.Key;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
private SeekBar volumeSeekbar = null;
private AudioManager audioManager = null;
int Volume=0;
ImageView aboutImage;
private Button buttonStart;
private Button buttonStop;
private Button buttonPause;
public static final String CHANNEL_ID = "exampleServiceChannel";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setVolumeControlStream(AudioManager.STREAM_MUSIC);
setContentView(R.layout.activity_main);
initControls();
buttonStart = (Button) findViewById(R.id.buttonStart);
buttonStop = (Button) findViewById(R.id.buttonStop);
// buttonPause = (Button)findViewById(R.id.buttonPause);
aboutImage = (ImageView) findViewById(R.id.about);
buttonStart.setOnClickListener(this);
buttonStop.setOnClickListener(this);
aboutImage.setOnClickListener(this);
}
@Override
public void onClick(View v) {
if (v == buttonStart) {
startService(new Intent(this, RathuMakara.class));
buttonStart.setEnabled(false);
buttonStop.setEnabled(true);
Toast play = Toast.makeText(getApplicationContext(), "හරි 3, 2, 1 ... සද්දෙට අහමු", Toast.LENGTH_LONG);
play.setGravity(Gravity.BOTTOM | Gravity.CENTER_HORIZONTAL, 0, 0);
play.show();
} else if (v == buttonStop) {
stopService(new Intent(this, RathuMakara.class));
Toast play = Toast.makeText(getApplicationContext(), "Stopping Play", Toast.LENGTH_SHORT);
play.setGravity(Gravity.BOTTOM | Gravity.CENTER_HORIZONTAL, 0, 0);
play.show();
buttonStop.setEnabled(false);
buttonStart.setEnabled(true);
} else if (v == aboutImage)
aboutImage = (ImageView) findViewById(R.id.about);
aboutImage.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent aboutIntent = new Intent(MainActivity.this, AboutActivity.class);
startActivity(aboutIntent);
}
});
/*else if (v == buttonPause){
onPause();
}*/
}
private void initControls()
{
try {
volumeSeekbar = (SeekBar) findViewById(R.id.sb);
audioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
volumeSeekbar.setMax(audioManager
.getStreamMaxVolume(AudioManager.STREAM_MUSIC));
volumeSeekbar.setProgress(audioManager
.getStreamVolume(AudioManager.STREAM_MUSIC));
volumeSeekbar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
@Override
public void onStopTrackingTouch(SeekBar arg0) {
Toast volume = Toast.makeText(getApplicationContext(), "Volume: " + Integer.toString(Volume), Toast.LENGTH_SHORT);
volume.setGravity(Gravity.BOTTOM | Gravity.CENTER_HORIZONTAL, 0, 0);
volume.show();
}
@Override
public void onStartTrackingTouch(SeekBar arg0) {
}
@Override
public void onProgressChanged(SeekBar arg0, int progress, boolean arg2) {
audioManager.setStreamVolume(AudioManager.STREAM_MUSIC,
Volume = progress , 0);
}
});
} catch (Exception e) {
e.printStackTrace();
}
}
public boolean onKeyDown(int keyCode, KeyEvent event){
AudioManager audio = (AudioManager)this.getSystemService(Context.AUDIO_SERVICE);
int currentVolume = audio.getStreamVolume(AudioManager.STREAM_MUSIC);
if (keyCode == KeyEvent.KEYCODE_VOLUME_UP){
volumeSeekbar.setProgress(currentVolume);
return false;
} else if (keyCode == KeyEvent.KEYCODE_VOLUME_DOWN){
volumeSeekbar.setProgress(currentVolume);
return false;
}
return super.onKeyDown(keyCode, event);
}
}RathuMakara.java (Service class)
package com.example.yomal.rathumakarafm;
import android.app.Notification;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.media.AudioManager;
import android.media.MediaPlayer;
import android.os.Build;
import android.os.IBinder;
import android.provider.SyncStateContract;
import android.support.annotation.Nullable;
import android.support.annotation.RequiresApi;
import android.support.v4.app.NotificationCompat;
import android.widget.SeekBar;
import android.widget.Toast;
import java.io.IOException;
import static com.example.yomal.rathumakarafm.MainActivity.CHANNEL_ID;
public class RathuMakara extends Service {
private MediaPlayer rathu;
@Nullable
@Override
public IBinder onBind(Intent intent) {
return null;
}
@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
@Override
public int onStartCommand(Intent intent,int flags , int startID){
String url ="http://206.189.34.189:8000/rathumakara.mp3";
MediaPlayer rathu = new MediaPlayer();
rathu.setAudioStreamType(AudioManager.STREAM_MUSIC);
try {
rathu.setDataSource(url);
rathu.prepare();
rathu.start();
Intent notificationIntent = new Intent(this, MainActivity.class);
PendingIntent pendingIntent = PendingIntent.getActivity(this,
0, notificationIntent, 0);
Intent playIntent = new Intent(this, MainActivity.class);
// PendingIntent playPending = PendingIntent.
Bitmap icon = BitmapFactory.decodeResource(getResources(),
R.drawable.logo);
Notification notification = new NotificationCompat.Builder(this, CHANNEL_ID)
.setContentTitle("රතු මකරා FM \uD83D\uDC32")
.setContentText("Now Playing")
.setSmallIcon(R.drawable.logo)
.setLargeIcon(icon)
.setOngoing(true)
// .addAction(android.R.drawable.ic_media_play, "Play", )
.setContentIntent(pendingIntent)
.build();
startForeground(1, notification);
}
catch (IOException e){
e.printStackTrace();
}catch (IllegalArgumentException e){
e.printStackTrace();
}catch (SecurityException e){
e.printStackTrace();
}catch (IllegalStateException e){
e.printStackTrace();
}
return START_NOT_STICKY;
}
@Override
public void onDestroy(){
rathu.stop();
}
}Update
LogCat
2018-10-16 23:00:21.892 20437-20437/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.yomal.rathumakarafm:remote, PID: 20437
java.lang.RuntimeException: Unable to stop service com.example.yomal.rathumakarafm.RathuMakara@78b36d4: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.media.MediaPlayer.stop()' on a null object reference
at android.app.ActivityThread.handleStopService(ActivityThread.java:4114)
at android.app.ActivityThread.-wrap27(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2025)
at android.os.Handler.dispatchMessage(Handler.java:108)
at android.os.Looper.loop(Looper.java:166)
at android.app.ActivityThread.main(ActivityThread.java:7425)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.media.MediaPlayer.stop()' on a null object reference
at com.example.yomal.rathumakarafm.RathuMakara.onDestroy(RathuMakara.java:113)
at android.app.ActivityThread.handleStopService(ActivityThread.java:4090)
at android.app.ActivityThread.-wrap27(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2025)
at android.os.Handler.dispatchMessage(Handler.java:108)
at android.os.Looper.loop(Looper.java:166)
at android.app.ActivityThread.main(ActivityThread.java:7425)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)
回答1:
Remove the word MediaPlayer from inside onStartCommand(). You declared a local variable with the same name as a member variable, causing the member variable to be "shadowed". That left it uninitialized, which caused an NPE in your onDestroy().
来源：https://stackoverflow.com/questions/52840281/app-stops-working-when-mediaplayer-is-stopped-in-service-class