Question

我尝试使用AsyncTask加载专辑封面，但我得到NullPointerException：

ImageLoader的：

public class ImageLoader extends AsyncTask<String, Void, Bitmap>{
    Context mcontext;
    private ImageView image;
    Cursor cursor;
    private Bitmap artwork = null;
    SongsListAdapter songsAdapter;

    public ImageLoader(ImageView image) {
        this.image = image;
    }

    protected Bitmap doInBackground(String... uri) {
        for (int i=0; i < songsAdapter.getCount(); i++) {
            cursor.moveToPosition(i);
            Uri sArtworkUri = Uri.parse("content://media/external/audio/albumart");
            Long albumid = cursor.getLong(cursor
                    .getColumnIndexOrThrow(MediaStore.Audio.Media.ALBUM_ID));
            Uri art = ContentUris.withAppendedId(sArtworkUri, albumid);
            ContentResolver res = mcontext.getContentResolver();
            InputStream in = null;
            try {
                in = res.openInputStream(art);
            } catch (FileNotFoundException e1) {
                e1.printStackTrace();
            }
            artwork = BitmapFactory.decodeStream(in);
        }
        return null;
    }

    protected void onPostExecute(Void arg) {
        // Display the image
        image.setImageBitmap(artwork);
    }
}

SongsListAdapter ：

public class SongsListAdapter extends BaseAdapter {

    private Context mContext;
    private ArrayList<MusikUntil> songList;

    public SongsListAdapter(Context context, ArrayList<MusikUntil> list) {
        this.mContext = context;
        this.songList = list;
    }

    public int getCount() {
        return songList.size();
    }

    public MusikUntil getItem(int position) {
        return null;
    }

    public long getItemId(int position) {
        return 0;
    }

    @SuppressLint("InflateParams")
    public View getView(int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            convertView = LayoutInflater.from(mContext).inflate(R.layout.song_item, null);
        }

        ImageView mImgIcon = (ImageView)convertView.findViewById(R.id.list_image);
        TextView mTxtJudul = (TextView)convertView.findViewById(R.id.Judul_Musik);
        TextView mTxtMusisi = (TextView)convertView.findViewById(R.id.Artis);

        new ImageLoader(mImgIcon).execute();
        mTxtJudul.setText(songList.get(position).getSongName());
        mTxtMusisi.setText(songList.get(position).getArtistName());

        return convertView;
    }

    public void setSongsList (ArrayList<MusikUntil> list) {
        songList = list;
        this.notifyDataSetChanged();
    }

}

logcat的：

Process: com.karyaanaknegeri.musikq, PID: 5736
java.lang.RuntimeException: An error occured while executing doInBackground()
        at android.os.AsyncTask$3.done(AsyncTask.java:304)
        at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
        at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
        at java.util.concurrent.FutureTask.run(FutureTask.java:242)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
        at java.lang.Thread.run(Thread.java:818)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int com.karyaanaknegeri.musikq.adapters.SongsListAdapter.getCount()' on a null object reference
        at com.karyaanaknegeri.musikq.loader.ImageLoader.doInBackground(ImageLoader.java:40)
        at com.karyaanaknegeri.musikq.loader.ImageLoader.doInBackground(ImageLoader.java:28)
        at android.os.AsyncTask$2.call(AsyncTask.java:292)
        at java.util.concurrent.FutureTask.run(FutureTask.java:237)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
        at java.lang.Thread.run(Thread.java:818)

Answer 1

<强> 1。 ImageLoader中的问题

您只声明了SongsListAdapter songsAdapter;。在使用之前，您必须首先初始化此对象。

您没有初始化Cursor cursor;，因此它也会抛出NullPointerException。

<强> 2。 SongsListAdapter中的问题

变化：

public MusikUntil getItem(int position) {
    return null;
}

public long getItemId(int position) {
    return 0;
}

到

public MusikUntil getItem(int position) {
    return songList.get(position);
}

public long getItemId(int position) {
    return position;
}

第3。提示

您的代码看起来像某些教程中的复制粘贴。如果您遇到AsyncTask问题，请尝试Picasso或Universal Image Loader for Android。这些库非常易于使用，可以帮助您处理加载图像。

如何在Java中调试java.lang.NullPointerException错误？

1 个答案: