Android load images from URL into custom listview adapter without Picasso

Question

I am trying to load images from a url and I have used Picasso, however I'd like to know how to do it without an external library if possible. I know I have to get an Asynctask going but I'm not sure how to implement it.

This is my getview code

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    View row = convertView;
    if(position==0){

        NewsObj currNews = news.get(position);
        DataHandler dh;
        if(convertView==null){
            LayoutInflater inflater = (LayoutInflater)this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            row = inflater.inflate(R.layout.firstnews,parent,false);
            dh = new DataHandler();
            dh.newsTitle = (TextView)row.findViewById(R.id.newsTitle);
            dh.newsDate = (TextView)row.findViewById(R.id.newsDate);
            dh.newsIcon = (ImageView)row.findViewById(R.id.newsIcon);
            row.setTag(dh);
        }else{
            dh = (DataHandler)row.getTag();
        }
        NewsObj no = (NewsObj)this.getItem(position);
        new AsyncDownloadTask().execute(row,no.getImgurl());
        dh.newsTitle.setText(no.getTitle());
        dh.newsDate.setText(no.getDate());

    }else{

        NewsObj currNews = news.get(position);
        DataHandler dh;
        if(convertView==null){
            LayoutInflater inflater = (LayoutInflater)this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            row = inflater.inflate(R.layout.newslist,parent,false);
            dh = new DataHandler();
            dh.newsTitle = (TextView)row.findViewById(R.id.newsTitle);
            dh.newsDate = (TextView)row.findViewById(R.id.newsDate);
            dh.newsIcon = (ImageView)row.findViewById(R.id.newsIcon);
            row.setTag(dh);
        }else{
            dh = (DataHandler)row.getTag();
        }
        NewsObj no = (NewsObj)this.getItem(position);
        new AsyncDownloadTask().execute(row,no.getImgurl());

        dh.newsTitle.setText(no.getTitle());
        dh.newsDate.setText(no.getDate());

    }
    return row;
}


 private class AsyncDownloadTask extends AsyncTask<Object, String, Bitmap>{

    private View view;
    private Bitmap bitmap = null;
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected void onPostExecute(Bitmap bitmap) {
        if(bitmap!=null&&view!=null){
            ImageView newsIcon = (ImageView)view.getTag(R.id.newsIcon);
            newsIcon.setImageBitmap(bitmap);
        }
    }

    @Override
    protected Bitmap doInBackground(Object... params) {
        view = (View)params[0];
        String uri = (String)params[1];
        try{
            InputStream inputStream = new URL(uri).openStream();
            bitmap = BitmapFactory.decodeStream(inputStream);
        }catch (Exception e){
            e.printStackTrace();
        }
        return bitmap;
    }
}

This is my async task

UPDATE : Encountering null pointer exceptions

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageBitmap(android.graphics.Bitmap)' on a null object reference

Answer 1

You can write your own code. But using a library handles all the boilerplate code which is associated with a library. Unless otherwise, I also recommend that you use a library. Here are some of the boilerplate things that you need to consider when writing your own code.

1. Memory management: External libraries take care of making sure the images doesn't take up all of the memory available for your app. Android Bitmaps are very memory conscious to deal with and therefore better to give this part to a library.

2. Handling activity destruction: If you rotate your phone while an image download is in progress, it will recreate the activity and then you will need to handle cancellation of the previous requests and start them again.

3. Cancelling previous requests: Image libraries are written such that list view items which are no longer visible do not continue downloading. Suppose you scroll down. Then there is no point in downloading the images which are part of the first rows. You should cancel such downloads and start downloading the new images. Image downloader libraries are written to take care of these.

4. Caching: The image libraries use both a memory cache and a disk cache to store the downloaded bitmaps. Therefore, they only download new images unless they are not available.

5. Loading large bitmaps off the UI Thread: Suppose your app includes large Bitmaps. In order to load them into your view, you must first load them from disk. You need to write code so that loading them do not block the main UI thread.

6. Loading relevant image sizes: Your application may run either a new Android device with high screen density or an old device with low screen density. Depending on your target device, you won't need to load a full resolution image if your device does not support such screen density. Usually libraries handle this for you,

These are just a few of the boilerplate stuff to consider. Therefore, I highly recommend that you use a good library for the image loading part unless it's so so required!!!

Answer 2

Simply you can use java.net.URL for loading an image into ImageView like

    ImageView loadedImage;

    @override
    protected Bitmap doInBackground(String... url) {
        String URL_OF_IMAGE = url[0];
        Bitmap bitmap = null;
        try {
            InputStream in = new java.net.URL(URL_OF_IMAGE).openStream();
            bitmap= BitmapFactory.decodeStream(in);
        } catch (Exception e) {
        }
        return bitmap;
    }

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

But notice that you should have extend AsyncTask that should have first parameter as String and last as Bitmap like

private class DowmloadImage extends AsyncTask<String, Void, Bitmap>

Answer 3

You can Use Network Image View instead of Imageview. It surely makes your life easier.

<com.android.volley.toolbox.NetworkImageView
    android:id="@+id/networkImageView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerHorizontal="true"
    android:background="#000000"/>

This should be replaced in place of Image view in the required XML File.

public ImageLoader getImageLoader() {
    getRequestQueue();
    if (mImageLoader == null) {
        mImageLoader = new ImageLoader(this.mRequestQueue,
                new LruBitmapCache());
    }
    return this.mImageLoader;
}

The class above also creates an ImageCache which works with normal volley cache, but only caching images for requests.

To Set the Image URL.

advImage.setImageUrl("Your Image URL", AppController.getInstance().getImageLoader());

Call the Image Loader Function accordingly. You can also set the defalult placeholder image as well.