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我正在制作一个 android 应用程序，它将文件从 sdcard 上的目录加载到列表中。一旦一个项目被点击，它就会解析它的路径，并将其放入一个字符串中。我正在尝试使用 .SetDataSource() 方法将字符串加载到媒体播放器中，但它会强制关闭并导致异常。我怎样才能解决这个问题？请帮助我，谢谢！代码如下：

package com.mysoftwaremobileapps.Cross;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import android.app.ListActivity;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListAdapter;
import android.widget.ListView;

public class MusicActivity extends ListActivity {
//Called when the activity is first created
List<String> myList = new ArrayList<String>();
EditText AddItemToListViewEditText;
  static final String[] COUNTRIES = new String[] {
      "Movies"
      };
  MediaPlayer mp1;
  String musicUri;
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.musicscreen);

    //Setup ListView
    setListAdapter((ListAdapter) new ArrayAdapter<String>(this, R.layout.list_item, COUNTRIES));
    setListAdapter((ListAdapter) new ArrayAdapter<String>(this, R.layout.list_item, myList));

    ListView lv = getListView();
    lv.setTextFilterEnabled(true);

    File mFile = new File(Environment.getExternalStorageDirectory() + "/Music/");
    myList.addAll(Arrays.asList(mFile.list()));
    setListAdapter((ListAdapter) new ArrayAdapter<String>(this, R.layout.list_item, myList));


    lv.setOnItemClickListener(new OnItemClickListener() {
      public void onItemClick(AdapterView<?> parent, View view,
          int position, long id) {
        //When an item is clicked, play it on a MediaPlayer
          try {
              musicUri = Environment.getExternalStorageDirectory() + "/Music/" + myList.get(position);
            mp1.setDataSource(musicUri);
        } catch (IllegalArgumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalStateException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
  }
    });
}
}

日志猫：

    07-03 21:25:42.031: D/ViewConsistency(5165): AbsListView android.widget.ListView@40588c48 enabled= true
07-03 21:25:42.051: D/ViewConsistency(5165): AbsListView android.widget.ListView@40588c48 enabled= true
07-03 21:25:43.691: D/AndroidRuntime(5165): Shutting down VM
07-03 21:25:43.691: W/dalvikvm(5165): threadid=1: thread exiting with uncaught exception (group=0x40015560)
07-03 21:25:43.721: E/AndroidRuntime(5165): FATAL EXCEPTION: main
07-03 21:25:43.721: E/AndroidRuntime(5165): java.lang.NullPointerException
07-03 21:25:43.721: E/AndroidRuntime(5165):     at com.mysoftwaremobileapps.Cross.MusicActivity$1.onItemClick(MusicActivity.java:52)
07-03 21:25:43.721: E/AndroidRuntime(5165):     at android.widget.AdapterView.performItemClick(AdapterView.java:284)
07-03 21:25:43.721: E/AndroidRuntime(5165):     at android.widget.ListView.performItemClick(ListView.java:3513)
07-03 21:25:43.721: E/AndroidRuntime(5165):     at android.widget.AbsListView$PerformClick.run(AbsListView.java:1877)
07-03 21:25:43.721: E/AndroidRuntime(5165):     at android.os.Handler.handleCallback(Handler.java:587)
07-03 21:25:43.721: E/AndroidRuntime(5165):     at android.os.Handler.dispatchMessage(Handler.java:92)
07-03 21:25:43.721: E/AndroidRuntime(5165):     at android.os.Looper.loop(Looper.java:130)
07-03 21:25:43.721: E/AndroidRuntime(5165):     at android.app.ActivityThread.main(ActivityThread.java:3835)
07-03 21:25:43.721: E/AndroidRuntime(5165):     at java.lang.reflect.Method.invokeNative(Native Method)
07-03 21:25:43.721: E/AndroidRuntime(5165):     at java.lang.reflect.Method.invoke(Method.java:507)
07-03 21:25:43.721: E/AndroidRuntime(5165):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:864)
07-03 21:25:43.721: E/AndroidRuntime(5165):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:622)
07-03 21:25:43.721: E/AndroidRuntime(5165):     at dalvik.system.NativeStart.main(Native Method)
07-03 21:25:45.171: I/Process(5165): Sending signal. PID: 5165 SIG: 9
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1 回答 1

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您从未实例化 MediaPlayer 对象，这正是抛出您得到的 NPE 的原因；你只留下它：MediaPlayer m1p

在设置数据源之前，您需要使用以下命令对其进行实例化：

 m1p = new MediaPlayer();
于 2012-07-03T19:42:39.637 回答