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using asynctask to load images in listview


using asynctask to load images in listview  using -'android,android-listview,android-asynctask,android-adapter'

I have one ListView which can hold an image. It depends if image exists or not in SDCARD.

Here my example code:

public class MainActivity extends Activity  {

    ListView mListView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mListView = new ListView(this);
        setContentView(mListView);

        String[] arr = new String[] {
                "/example/images/1.jpg", "/example/images/2.jpg",  
                "/example/images/3.jpg", "/example/images/4.jpg",  
                "/example/images/5.jpg", "/example/images/6.jpg",
                "/example/images/7.jpg", "/example/images/8.jpg",  
                "/example/images/9.jpg", "/example/images/1.jpg",
                "/example/images/2.jpg", "/example/images/3.jpg",  
                "/example/images/4.jpg", "/example/images/5.jpg",  
                "/example/images/6.jpg", "/example/images/7.jpg",  
                "/example/images/8.jpg", "/example/images/9.jpg",
                "/example/images/1.jpg", "/example/images/2.jpg",  
                "/example/images/3.jpg", "/example/images/4.jpg",  
                "/example/images/5.jpg", "/example/images/6.jpg",
                "/example/images/7.jpg", "/example/images/8.jpg",  
                "/example/images/9.jpg", "/example/images/1.jpg",
                "/example/images/2.jpg", "/example/images/3.jpg",  
                "/example/images/4.jpg", "/example/images/5.jpg",  
                "/example/images/6.jpg", "/example/images/7.jpg",  
                "/example/images/8.jpg", "/example/images/9.jpg"};

        List<String> list = Arrays.asList(arr);

        MyAdapter adapter = new MyAdapter(this, R.layout.listitem_imv, list);

        mListView.setAdapter(adapter);
    }

    class MyAdapter extends ArrayAdapter<String>{

        List<String> mList;
        LayoutInflater mInflater;
        int mResource;

        public MyAdapter(Context context, int resource,
                List<String> objects) {
            super(context, resource, objects);

            mResource = resource;
            mInflater = getLayoutInflater();
            mList = objects;
        }

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

            if(convertView == null){
                view = mInflater.inflate(mResource, null);
            }else{
                view = convertView;
            }

            ImageView imageView = (ImageView) view.findViewById(R.id.imv);
            TextView textView = (TextView) view.findViewById(R.id.txv);

                            imageView.setTag(mList.get(position));//tag of imageView == path to image
            new LoadImage().execute(imageView);
            textView.setText(mList.get(position).toString());

            return view;
        }       
    }

    class LoadImage extends AsyncTask<Object, Void, Bitmap>{

        private ImageView imv;
        private String path;


        @Override
        protected Bitmap doInBackground(Object... params) {
            imv = (ImageView)   params[0];

            path = imv.getTag().toString();

            Bitmap bitmap = null;
            File file = new File(
                    Environment.getExternalStorageDirectory().getAbsolutePath() + path);

            if(file.exists()){
                bitmap = BitmapFactory.decodeFile(file.getAbsolutePath());
            }

            return bitmap;
        }
        @Override
        protected void onPostExecute(Bitmap result) {
            if(result != null && imv != null){
                imv.setVisibility(View.VISIBLE);
                imv.setImageBitmap(result);
            }else{
                imv.setVisibility(View.GONE);
            }
        }
    }
}


The 'sdcard/example/images' directory has the images: 1.jpg, 2.jpg, 3.jpg, 4.jpg, 6.jpg, 7.jpg and 9.jpg.
the expected result is:


But, if I scroll the list quickly, some images are inserted in the wrong items.
It happens due to use of convertView in getView() method.

If I use the following code, the code works fine:

        //if(convertView == null){
        //  view = mInflater.inflate(mResource, null);
        //}else{
        //  view = convertView;
        //}
        view = mInflater.inflate(mResource, null);


When list scrolled quickly, two asyncTasks can reference one same View, due to use of convertView.
How Can I cancel AsyncTask when the View is no longer visible?(and is useb by another item of ListView)

edit

            @Override
    protected void onPostExecute(Bitmap result) {
        if(result != null && imv != null){

            if(imv.getTag().equals(path)){
                imv.setVisibility(View.VISIBLE);
                imv.setImageBitmap(result);
            }else{
                imv.setVisibility(View.GONE);
            }

        }else{
            imv.setVisibility(View.GONE);
        }
    }

    
asked Sep 21, 2015 by deepak07.s
0 votes
38 views



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