imageView获取图片空指针异常

Question

通过URL获取图片时，然后在imageView中设置，结果系统给我报出空指针异常。

请高手帮忙解决一下，谢谢。

public class DetailsActivity extends Activity {
    ImageView thumbnail = (ImageView) findViewById(R.id.btnThumbnail);
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.detail);

        final Bundle extras = getIntent().getExtras();
        String img = extras.getString("Thumbnail");
        new DownloadImageTask((ImageView) findViewById(R.id.btnThumbnail))
                .execute("http://mysite.com/images/"
                        + img);

        }
    class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {

        public DownloadImageTask(ImageView bmImage) {
            thumbnail = bmImage;
        }

        protected Bitmap doInBackground(String... urls) {
            String urldisplay = urls[0];
            Log.e("URL",urldisplay);
            Bitmap mIcon11 = null;
            try {
                InputStream in = new java.net.URL(urldisplay).openStream();
                mIcon11 = BitmapFactory.decodeStream(in);
            } catch (Exception e) {
                Log.e("Error", e.getMessage());
                e.printStackTrace();
            }
            return mIcon11;
        }

        protected void onPostExecute(Bitmap result) {
            thumbnail.setImageBitmap(result);
        }
    }

}

Answer 1

写法没问题，只不过thumbnail不应该在外部去查找指向他的id
ImageView thumbnail = (ImageView) findViewById(R.id.btnThumbnail);
改成：
ImageView thumbnail即可