从自定义适配器调用AsyncTask

Question

I have created a listview with a custom adapter. One of the fields is an image to show the avatar of each user. I must obtain those images from an url.

I have created a class that converts an image from URL into a Bitmap.

I think this should be done from an asyntask. The problem is that I do not know how to call this method from a custom adapter.

This is my class:

private class obtAvatar2 extends AsyncTask<Void , Void, Bitmap>{
    Bitmap bm;

    @Override
    protected Bitmap doInBackground(Void... voids) {
        try {

            URL url = new URL("https://www.bellatores.cl/wp-content/uploads/2018/01/Avatar-Mujer.png");
            URLConnection con = url.openConnection();
            con.connect();
            InputStream is = con.getInputStream();
            BufferedInputStream bis = new BufferedInputStream(is);
            bm = BitmapFactory.decodeStream(bis);
            bis.close();
            is.close();

        }catch (IOException e){

        }

        return bm;
    }
}

This return a Bitmap. Then from my custom adapter, i need to put that Bitmap in a ImageView

for example, i'm trying:

ImageView avatarView = (ImageView)view.findViewById(R.id.imageViewAvatarMensa);
avatarView.setImageBitmap(new obtAvatar2().execute());

But, it's wrong :(

any advice?

Answer 1

I suggest to you to either work with Glide or Picasso libaries, they are the most used image library on android application :

To import to you project with gradle :

PICASSO :

dependencies {
    compile 'com.squareup.picasso:picasso:2.5.1'
}

GLIDE :

dependencies {
    compile 'com.github.bumptech.glide:glide:3.5.2'
}

Usage :

PICASSO :

Picasso.with(myFragment)
    .load(url)
    .into(myImageView);

GLIDE :

Glide.with(myFragment)
    .load(url)
    .into(myImageView);

Hope this helps

Answer 2

You can use Glide or Picasso . As those are very helpful libraries for setting image in adapter (here views are reusable).

If you still want to use asynctask then check below:

In adapter each time scroll will lead to new network call, that can be avoided using saving bitmap object.

You are trying to get image by using below code:

ImageView avatarView = (ImageView)view.findViewById(R.id.imageViewAvatarMensa);
avatarView.setImageBitmap(new obtAvatar2().execute());

This will not work as:

new obtAvatar2().execute()

It will execute in background and return response in onPostExucute() . And result is:

avatarView.setImageBitmap(null)

If you want to use asytask then probably you need make your code like:

private class obtAvatar2 extends AsyncTask<Void, Void, Bitmap> {
        Bitmap bm;

        @Override
        protected Bitmap doInBackground(Void... voids) {
            try {

                URL url = new URL("https://www.bellatores.cl/wp-content/uploads/2018/01/Avatar-Mujer.png");
                URLConnection con = url.openConnection();
                con.connect();
                InputStream is = con.getInputStream();
                BufferedInputStream bis = new BufferedInputStream(is);
                bm = BitmapFactory.decodeStream(bis);
                bis.close();
                is.close();

            } catch (IOException e) {

            }

            return bm;
        }

        @Override
        protected void onPostExecute(Bitmap bitmap) {
            super.onPostExecute(bitmap);
            ImageView avatarView = (ImageView)view.findViewById(R.id.imageViewAvatarMensa);
                avatarView.setImageBitmap(bitmap);
                //set bitmap to imageview and save in local list, so in future no need to download
            }
        }

You can pass reference of ImageView in constructor.

Answer 3

First of all you should add obtAvatar2 async task in your custom adapter.

I hope you are using ViewHolder in your customadapter, then in you getView(), before assigning value to your Imageview, call the async task. For example:

 public static class ViewHolder {

    public ImageView display_adImage;

}

public View getView(final int position, View convertView, ViewGroup parent) {
    View vi = convertView;

    try {
        if (convertView == null) {

            vi = inflater.inflate(R.layout.test_layout, null);
            holder = new ViewHolder();

            holder.display_adImage = vi.findViewById(R.id.IvAdImage);


            vi.setTag(holder);
        } else {
            holder = (ViewHolder) vi.getTag();
        }

        ...


        Bitmap b =  new GetImageTask().execute().get();
    holder.display_adImage.setImageBitmap(b);
}
}

 private class obtAvatar2 extends AsyncTask<Void , Void, Bitmap>{
Bitmap bm;

@Override
protected Bitmap doInBackground(Void... voids) {
    try {

        URL url = new URL("https://www.bellatores.cl/wp-content/uploads/2018/01/Avatar-Mujer.png");
        URLConnection con = url.openConnection();
        con.connect();
        InputStream is = con.getInputStream();
        BufferedInputStream bis = new BufferedInputStream(is);
        bm = BitmapFactory.decodeStream(bis);
        bis.close();
        is.close();

    }catch (IOException e){

    }

    return bm;
}

}