ListView like in universal image loader sample app

问题:

I am using universal image loader for displaying thumb images in the list view. I have implemented the basic steps in the adapter and everything is working. The problem is if i have 10 items in the list and i can see first 5 as soon as i scroll down new images are displayed but when i scroll back up the images are replaced again with correct once , what i want is first 5 images which are shown at the starting should not be replaced . So that when i scroll back up and down the images are not replaced again and again .

Like it is done in the uil sample app ListActivity , the images once loaded are not replaced when scroll back up.

Here is the code

Application class

public class MyApplication extends Application {

@Override
public void onCreate() {
    // TODO Auto-generated method stub
    super.onCreate();

    // Create default options which will be used for every 
   //  displayImage(...) call if no options will be passed to this method
    DisplayImageOptions displayimageOptions = new DisplayImageOptions.Builder().cacheInMemory().cacheOnDisc().build();


    // Create global configuration and initialize ImageLoader with this configuration
    ImageLoaderConfiguration config = new ImageLoaderConfiguration.Builder(getApplicationContext()).
            defaultDisplayImageOptions(displayimageOptions).build();
    ImageLoader.getInstance().init(config);
}
}

Adapter

public class CarListAdapter extends BaseAdapter {

private ArrayList<CarDetail> items = new ArrayList<CarDetail>();
private Context context;
private ImageLoader imageLoader;
private ImageLoadingListener animateFirstDisplayListener;



public CarListAdapter(Context context , ArrayList<CarDetail> items , ImageLoadingListener animateFirstDisplayListener) {
    super();
    this.context = context;
    this.items = items;
    this.animateFirstDisplayListener = animateFirstDisplayListener;
    imageLoader = ImageLoader.getInstance();
    imageLoader.init(ImageLoaderConfiguration.createDefault(context));

}

@Override
public int getCount() {
    // TODO Auto-generated method stub
    return items.size();
}

@Override
public Object getItem(int position) {
    // TODO Auto-generated method stub
    return items.get(position);
}

@Override
public long getItemId(int position) {
    // TODO Auto-generated method stub
    return position;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    // TODO Auto-generated method stub
    Log.d("Inside", "GetView");

    LayoutInflater mInflater = (LayoutInflater)context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
    ViewHolder holder = null;
    final CarDetail car = items.get(position);


     if (convertView == null) {

            convertView = mInflater.inflate(R.layout.car_list_row, parent , false);
            holder = new ViewHolder();
            holder.tvCarName = (TextView) convertView.findViewById(R.id.tvCarName);
            holder.tvDailyPriceValue = (TextView) convertView.findViewById(R.id.tvDailyPriceValue);
            holder.tvWeeklyPriceValue = (TextView) convertView.findViewById(R.id.tvWeeklyPriceValue);
            holder.tvWeekendPriceValue = (TextView) convertView.findViewById(R.id.tvWeekendPriceValue);
            holder.imgCar = (ImageView) convertView.findViewById(R.id.imgCar);
            holder.btnBookNow = (Button) convertView.findViewById(R.id.btnBookNow);

            holder.btnBookNow.setFocusable(false);
            holder.btnBookNow.setFocusableInTouchMode(false);

            holder.btnBookNow.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View arg0) {
                    // TODO Auto-generated method stub
                    Intent intent = new Intent(context , BookingFormActivity.class);
                    intent.putExtra("car_name", car.getCarName());
                    intent.putExtra("min_age", car.getMinimumAge());
                    context.startActivity(intent);
                }
            });

            convertView.setTag(holder);
    }
     else {

         holder = (ViewHolder) convertView.getTag();
        }

     holder.tvCarName.setText(car.getCarName());
     holder.tvDailyPriceValue.setText(car.getDailyPrice());
     holder.tvWeeklyPriceValue.setText(car.getWeeklyPrice());
     holder.tvWeekendPriceValue.setText(car.getWeekendPrice());
     imageLoader.displayImage(car.getThumbUrl(), holder.imgCar, animateFirstDisplayListener);


  return convertView;
 }

 static class ViewHolder {

            TextView tvCarName;
            TextView tvDailyPriceValue;
            TextView tvWeeklyPriceValue;
            TextView tvWeekendPriceValue;
            ImageView imgCar;
            Button btnBookNow;
        }




}

回答1:

You are calling init() twice, and the second call overrides your caching options. Remove this line:

imageLoader.init(ImageLoaderConfiguration.createDefault(context));

回答2:

Use Lazy Listadapter it is easy and efficient link below https://github.com/thest1/LazyList/blob/master/src/com/fedorvlasov/lazylist/LazyAdapter.java