Android:如何访问音频文件？

Question

在我的应用程序中，我使用此方法来访问音频文件:

public Cursor pobierzPlikiAudio(){
    String[] STAR = {"*"};
    String selection = MediaStore.Audio.Media.IS_MUSIC + " != 0";
    Uri uri= Uri.parse("content://pl/aplikacja/app/provider/MediaStore/Audio");
    return getContentResolver().query(uri, STAR, selection, null, null);
}

但在我的 LogCat 中我得到一个 nullPointerException。怎么了？

Logcat 出现错误:

10-29 07:04:17.729: E/AndroidRuntime(24354): FATAL EXCEPTION: main
10-29 07:04:17.729: E/AndroidRuntime(24354): java.lang.RuntimeException: Unable to start activity ComponentInfo{pl.aplikacja.app/pl.aplikacja.app.MainActivity}: java.lang.NullPointerException
10-29 07:04:17.729: E/AndroidRuntime(24354):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1967)
10-29 07:04:17.729: E/AndroidRuntime(24354):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1992)
10-29 07:04:17.729: E/AndroidRuntime(24354):    at android.app.ActivityThread.access$600(ActivityThread.java:127)
10-29 07:04:17.729: E/AndroidRuntime(24354):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1158)
10-29 07:04:17.729: E/AndroidRuntime(24354):    at android.os.Handler.dispatchMessage(Handler.java:99)
10-29 07:04:17.729: E/AndroidRuntime(24354):    at android.os.Looper.loop(Looper.java:137)
10-29 07:04:17.729: E/AndroidRuntime(24354):    at android.app.ActivityThread.main(ActivityThread.java:4441)
10-29 07:04:17.729: E/AndroidRuntime(24354):    at java.lang.reflect.Method.invokeNative(Native Method)
10-29 07:04:17.729: E/AndroidRuntime(24354):    at java.lang.reflect.Method.invoke(Method.java:511)
10-29 07:04:17.729: E/AndroidRuntime(24354):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
10-29 07:04:17.729: E/AndroidRuntime(24354):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
10-29 07:04:17.729: E/AndroidRuntime(24354):    at dalvik.system.NativeStart.main(Native Method)
10-29 07:04:17.729: E/AndroidRuntime(24354): Caused by: java.lang.NullPointerException
10-29 07:04:17.729: E/AndroidRuntime(24354):    at pl.aplikacja.app.MainActivity.onCreate(MainActivity.java:18)
10-29 07:04:17.729: E/AndroidRuntime(24354):    at android.app.Activity.performCreate(Activity.java:4465)
10-29 07:04:17.729: E/AndroidRuntime(24354):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
10-29 07:04:17.729: E/AndroidRuntime(24354):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1931)
10-29 07:04:17.729: E/AndroidRuntime(24354):    ... 11 more

这是 MainActivity.java

package pl.aplikacja.app;

import android.os.Bundle;
import android.database.Cursor;
import android.app.Activity;
import android.view.Menu;
import android.widget.TextView;
import android.provider.MediaStore;

public class MainActivity extends Activity {

    private Dostawca dostawca;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

       Cursor tablicaPlikow = dostawca.pobierzPlikiAudio();

       if (tablicaPlikow.moveToFirst()) {

           String title; 
           String artist;  
           String album; 
           int titleColumn = tablicaPlikow.getColumnIndex(MediaStore.EXTRA_MEDIA_TITLE); 
           int artistColumn = tablicaPlikow.getColumnIndex(MediaStore.EXTRA_MEDIA_ARTIST);
           int albumColumn =tablicaPlikow.getColumnIndex(MediaStore.EXTRA_MEDIA_ALBUM); 


               // Get the field values
               title = tablicaPlikow.getString(titleColumn);
               artist = tablicaPlikow.getString(artistColumn); 
               album = tablicaPlikow.getString(albumColumn);

         TextView widok = (TextView) findViewById(R.id.tekst);
         widok.setText(""+title+" "+ artist + " " + album);
   } 

        setContentView(R.layout.activity_main);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }
}

Answer 1

我认为您输入了错误的 uri。在此 Uri 上没有媒体文件，这就是您收到空指针异常的原因。请点击以下链接
GetMedia Information