java - 下面的代码中 asynctask 是否正确使用？

Question

i am trying to use asynctask to download images from internet.i have this in my custom pager adapter which sets imageview with the image downloaded.

哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈)哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈

 public class pageradapter extends PagerAdapter {
    Button load_img;
    ImageView imgview;
    Bitmap bitmap;



    Context mContext;
    LayoutInflater mLayoutInflater;
    List<String> l = MainActivity.list;
    ImageLoader mImageLoader;

    public pageradapter(Context context) {
        mContext = context;


    }

    @Override
    public int getCount() {
        return 4;
    }


    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        ImageLoader mImageLoader = ImageLoader.getInstance();
        mLayoutInflater = ((LayoutInflater) container.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE));
        View view = mLayoutInflater.inflate(R.layout.img, container, false);
          imgview = (ImageView) view.findViewById(R.id.imageView3);

   new LoadImage().execute(l.get(position));


        container.addView(view);

        return view;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        container.removeView((LinearLayout) object);
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return view == object;
    }

    public class LoadImage extends AsyncTask<String, String, Bitmap> {

        ProgressDialog pDialog = new ProgressDialog(mContext);
        @Override
        protected void onPreExecute() {
            super.onPreExecute();

            pDialog.setMessage("Loading Image ....");
            pDialog.show();

        }
        protected Bitmap doInBackground(String... args) {

            try {
                bitmap = BitmapFactory.decodeStream((InputStream) new URL(args[0]).getContent());

            } catch (Exception e) {
                e.printStackTrace();
            }
            return bitmap;
        }

        protected void onPostExecute(Bitmap image) {

            if(image != null){
                imgview.setImageBitmap(image);
                pDialog.dismiss();

            }else{

                pDialog.dismiss();
                Toast.makeText(mContext, "Image Does Not exist or Network Error", Toast.LENGTH_SHORT).show();

            }
        }
    }

}

images do not appear in the view pager.

Answer 1

您应该更改您的 LoadImage 类。

 public class LoadImage extends AsyncTask<String, Void, Bitmap> {  
    ImageView view;

    public LoadImage(ImageView view){
        this.view = view;
    }

    ProgressDialog pDialog = new ProgressDialog(mContext);
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog.setMessage("Loading Image ....");
        pDialog.setCancelable(false);
        pDialog.show();

    }
    protected Bitmap doInBackground(String... args) {

        try {
            URL URL = new URL(args[0]);
            URLConnection connection = URL.openConnection();
            connection.connect();
            InputStream input = new BufferedInputStream(URL.openStream());
            return BitmapFactory.decodeStream(input);
        } catch (Exception e) {}
        return null;
    }

    protected void onPostExecute(Bitmap image) {
        if (pDialog.isShowing())
            pDialog.dismiss();

        if(image != null){
            view.setImageBitmap(image);

        }else{
            Toast.makeText(mContext, "Image Does Not exist or Network Error", Toast.LENGTH_SHORT).show();
        }
    }
}

像这样使用它:

new LoadImage(imgview).execute(l.get(position));