尝试从远程MP3文件检索元数据时出错Android

Question

我正在为Android安装Radio Streming应用程序。 音乐很好地被MediaPlayer类播放，但问题是当我尝试检索元数据，应用程序块并返回错误时。 这是代码：

package com.tests.mediaplayer1; 
import java.io.IOException; 
import android.media.AudioManager; 
import android.media.MediaMetadataRetriever; 
import android.media.MediaPlayer; 
import android.os.Bundle; 
import android.app.Activity; 
import android.content.Context; 
import android.util.Log; 
import android.view.Menu; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.widget.SeekBar; 
import android.widget.SeekBar.OnSeekBarChangeListener; 
import android.widget.TextView; 

public class MainActivity extends Activity { 

private Button btn_prev; 
private Button btn_pause; 
private Button btn_play; 
private Button btn_next; 
private TextView txt_song_title; 
private SeekBar seekBar_volume; 

private MediaPlayer mediaPlayer; 
private MediaMetadataRetriever retriever; 
private String url = "http://support.k-designed.net/test-z/music/Accordossie.mp3"; 
private AudioManager audioManager; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    btn_prev = (Button) findViewById(R.id.btn_prev); 
    btn_pause = (Button) findViewById(R.id.btn_pause); 
    btn_play = (Button) findViewById(R.id.btn_play); 
    btn_next = (Button) findViewById(R.id.btn_next); 
    txt_song_title = (TextView) findViewById(R.id.txt_song_title); 
    seekBar_volume = (SeekBar) findViewById(R.id.seekBar_volume); 
    mediaPlayer = new MediaPlayer(); 
    mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC); 

    audioManager = (AudioManager)getSystemService(Context.AUDIO_SERVICE); 
    int maxVolume = audioManager.getStreamMaxVolume(AudioManager.STREAM_MUSIC); 
    int curVolume = audioManager.getStreamVolume(AudioManager.STREAM_MUSIC); 

    seekBar_volume.setMax(maxVolume); 
    seekBar_volume.setProgress(curVolume); 

    seekBar_volume.setOnSeekBarChangeListener(new OnSeekBarChangeListener() { 

     @Override 
     public void onStopTrackingTouch(SeekBar seekBar) { 
      // TODO Auto-generated method stub 

     } 

     @Override 
     public void onStartTrackingTouch(SeekBar seekBar) { 
      // TODO Auto-generated method stub 

     } 

     @Override 
     public void onProgressChanged(SeekBar seekBar, int progress, 
       boolean fromUser) { 
      audioManager.setStreamVolume(AudioManager.STREAM_MUSIC, progress, 0); 

     } 
    }); 

    btn_play.setOnClickListener(new OnClickListener() { 

     @Override 
     public void onClick(View v) { 
      try { 
       mediaPlayer.setDataSource(url); 
       retriever.setDataSource(url); 
       mediaPlayer.prepare(); // might take long! (for buffering, etc) 
       mediaPlayer.start(); 
       txt_song_title.setText(retriever.extractMetadata(MediaMetadataRetriever.METADATA_KEY_TITLE)); 
      } catch(Exception e) { 
       e.printStackTrace(); 
      } 
     } 
    }); 

    btn_pause.setOnClickListener(new OnClickListener() { 

     @Override 
     public void onClick(View v) { 
      mediaPlayer.pause(); 

     } 
    }); 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.main, menu); 
    return true; 
} 
    } 

这是我的错误：

java.lang.IllegalStateException 
at android.media.MediaPlayer.setDataSource(Native Method) 
at com.tests.mediaplayer1.MainActivity$2.onClick(MainActivity.java:84) 
at android.view.View.performClick(View.java:2485) 
at android.view.View$PerformClick.run(View.java:9080) 
at android.os.Handler.handleCallback(Handler.java:587) 
at android.os.Handler.dispatchMessage(Handler.java:92) 
at android.os.Looper.loop(Looper.java:130) 
at android.app.ActivityThread.main(ActivityThread.java:3687) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:507) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625) 
at dalvik.system.NativeStart.main(Native Method) 

Answer 1

从错误代码，我们可以观察报告如下错误

java.lang.IllegalStateException 
at android.media.MediaPlayer.setDataSource(Native Method) 

如果您MediaPlayer执行native,IllegalStateException当MediaPlayer对象为空时抛出。

从源，如果我们检查retriever，我们可以观察到，你声明这个变量，但还没有创建的对象。在您的来源中，请在创建mediaPlayer对象之前尝试以下代码。

retreiver = new MediaMetadataRetriever(); 

随着这一变化，retriever对象将被创建和你的setDataSource即retriever.setDataSource(url);调用会成功。