Null pointer exception when getting image from url to put in imageview

问题

I'm getting my image through an URL and trying to set that to my imageView. But I'm getting a Null Pointer Exception. It is not even entering my asynchtask.

Is there something I'm doing wrong or not seeing?

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);
        }
    }

}

回答1:

ImageView thumbnail = (ImageView) findViewById(R.id.btnThumbnail);

You need to get your image after inflating the layout, otherwise findViewById will returns null :

ImageView thumbnail; 

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

来源：https://stackoverflow.com/questions/17095311/null-pointer-exception-when-getting-image-from-url-to-put-in-imageview