My listview lags when scrolling. It seems as the lazyload works but the lag happens everytime an image is shown.
I'm using the imageLoader found here http://www.androidhive.info/2012/02/android-custom-listview-with-image-and-text/ and this is my adapter:
public class EventAdapter extends ArrayAdapter<Event>{
public ListImageLoader imageLoader;
public DisplayImageOptions imgDispOpts;
private ArrayList<Event> objects;
public EventAdapter(Context context, int textViewResourceId, ArrayList<Event> objects,ListImageLoader imageLoader) {
super(context, textViewResourceId, objects);
this.objects = objects;
this.imageLoader = imageLoader;
}
/*
* we are overriding the getView method here - this is what defines how each
* list item will look.
*/
@SuppressLint("DefaultLocale")
@Override
public View getView(int position, View convertView, ViewGroup parent){
Event event = objects.get(position);
// assign the view we are converting to a local variable
View v = convertView;
ViewHolder holder;
// first check to see if the view is null. if so, we have to inflate it.
// to inflate it basically means to render, or show, the view.
if (v == null) {
LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
v = inflater.inflate(R.layout.list_row, null);
System.out.println("new Viewholder");
holder = new ViewHolder();
holder.listTimeString = (TextView) v.findViewById(R.id.listTimeString);
holder.date =(TextView) v.findViewById(R.id.Date);
holder.title = (TextView) v.findViewById(R.id.title);
holder.shortInfo = (TextView) v.findViewById(R.id.shortinfo);
holder.ageIcon = (ImageView) v.findViewById(R.id.listAgeIcon);
holder.thumb = (ImageView) v.findViewById(R.id.wideListImage);
holder.header = (RelativeLayout) v.findViewById(R.id.headerLayout);
holder.rowLayout = (RelativeLayout) v.findViewById(R.id.rowlayout);
holder.listVenueIcon = (ImageView) v.findViewById(R.id.listVenueIcon);
holder.eventRowLayout = (RelativeLayout) v.findViewById(R.id.eventrowlayout);
v.setTag(holder);
}
else{
holder = (ViewHolder) v.getTag();
}
/*
* Recall that the variable position is sent in as an argument to this method.
* The variable simply refers to the position of the current object in the list. (The ArrayAdapter
* iterates through the list we sent it)
*
* Therefore, i refers to the current Item object.
*/
if (event != null) {
// This is how you obtain a reference to the TextViews.
// These TextViews are created in the XML files we defined.
//SET FONTS
Typeface tf = Typeface.createFromAsset(getContext().getAssets(), "fonts/myriad.otf");
holder.title.setTypeface(tf);
holder.shortInfo.setTypeface(tf);
Typeface tf2 = Typeface.createFromAsset(getContext().getAssets(),"fonts/agencyr.ttf");
holder.date.setTypeface(tf2);
// check to see if each individual textview is null
// if not, assign some text!
if(event.isBig()){
//holder.rowLayout.getLayoutParams().height=230;
holder.shortInfo.setHeight(80);
holder.shortInfo.setMaxLines(5);
holder.shortInfo.setText(event.getInfo());
}
else{
//holder.rowLayout.getLayoutParams().height=125;
//holder.listVenueIcon.setImageResource(R.drawable.ikon_bar);
holder.shortInfo.setHeight(16);
holder.shortInfo.setMaxLines(1);
holder.shortInfo.setText(event.getInfo());
}
if(event.isClub()){
holder.listVenueIcon.setImageResource(R.drawable.ikon_klubb);
}
else{
holder.listVenueIcon.setImageResource(R.drawable.ikon_bar);
}
if (event.isNewDay()){
holder.date.setText(event.getDay().toUpperCase());
holder.header.setVisibility(View.VISIBLE);
} else{
holder.header.setVisibility(View.GONE);
}
if (holder.title != null){
holder.title.setText(event.getHost().toUpperCase());
}
if(holder.ageIcon!= null){
switch(Integer.parseInt(event.getAge())){
case(19):
holder.ageIcon.setImageResource(R.drawable.event_info_19);
break;
...
more cases
...
case(30):
holder.ageIcon.setImageResource(R.drawable.event_info_30);
break;
default:
holder.ageIcon.setImageResource(R.drawable.event_info_18);
break;
}
}
if(holder.thumb != null){
imageLoader.DisplayImage(event.getThumbURL(), holder.thumb);
}
if(holder.listTimeString != null){
String tempTimeString = event.getStartTime() + " - " + event.getEndTime();
holder.listTimeString.setText(tempTimeString);
}
}
// the view must be returned to our activity
return v;
}
static class ViewHolder{
RelativeLayout eventRowLayout;
TextView listTimeString;
TextView date;
TextView title;
TextView shortInfo;
ImageView ageIcon;
ImageView thumb;
RelativeLayout header;
RelativeLayout rowLayout;
ImageView listVenueIcon;
}
}
Any ideas?
EDIT: I am loading the imageURLs asynchronously at onCreate, this would be a perfect place to cache the images, can you see how this could be done using the ImageLoader in the link?
yes, resolving the lagging by using memory cache. You can read the origin post from here.
I've implement my EntryArrayAdapter, which uses memory caching to prevent slow and lag when scrolling a list view.
public class EntryArrayAdapter extends ArrayAdapter<JSONObject> {
private final Context context;
private final ArrayList<JSONObject> values;
private final LruCache<String, Bitmap> cache;
static class ViewHolder {
public TextView title;
public TextView city;
public TextView outlet;
public TextView service;
public ImageView photo;
}
public EntryArrayAdapter(Context context, ArrayList<JSONObject> values) {
super(context, R.layout.layout_list_item);
this.context = context;
this.values = values;
final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
// Use 1/8th of the available memory for this memory cache.
final int cacheSize = maxMemory / 8;
cache = new LruCache<String, Bitmap>(cacheSize) {
@Override
protected int sizeOf(String key, Bitmap bitmap) {
// The cache size will be measured in kilobytes rather than
// number of items.
return bitmap.getRowBytes() / 1024;
}
};
}
/* (non-Javadoc)
* @see android.widget.ArrayAdapter#getCount()
*/
@Override
public int getCount() {
return values != null ? values.size() : 0;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View rowView = convertView;
ViewHolder holder;
if (rowView == null) {
LayoutInflater inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
rowView = inflater.inflate(R.layout.layout_list_item, parent, false);
// set references
holder = new ViewHolder();
holder.title = (TextView) rowView.findViewById(R.id.titleText);
holder.city = (TextView) rowView.findViewById(R.id.cityText);
holder.outlet = (TextView) rowView.findViewById(R.id.outletText);
holder.service = (TextView) rowView.findViewById(R.id.visaMasterText);
holder.photo = (ImageView) rowView.findViewById(R.id.itemImage);
rowView.setTag(holder);
}
else {
holder = (ViewHolder) rowView.getTag();
}
try {
JSONObject obj = values.get(position);
Bitmap bmp = getBitmapFromMemCache(obj.getString("id"));
if (bmp == null) {
bmp = BitmapHelper.decodeSampledBitmapFromResource(obj.getString("photo"), 96, 96);
addBitmapToMemoryCache(obj.getString("id"), bmp);
}
holder.title.setText(obj.getString("title"));
holder.city.setText(obj.getString("city"));
holder.outlet.setText(obj.getString("outlet"));
holder.service.setText(obj.getString("service"));
holder.photo.setImageBitmap(bmp);
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return rowView;
}
public void addBitmapToMemoryCache(String key, Bitmap bitmap) {
if (getBitmapFromMemCache(key) == null) {
cache.put(key, bitmap);
}
}
public Bitmap getBitmapFromMemCache(String key) {
return cache.get(key);
}
I solved it by caching the image in background by creating and using the following function in ImageLoader.java
public void cacheImage(String url){
Bitmap bmp = getBitmap(url);
memoryCache.put(url, bmp);
}
I created one instance of ImageLoader, made a static reference to it and then called
AsyncClass.imageLoader.cacheImage(url);
Where AsyncClass is the class where I made the static reference to the ImageLoader and called it "imageLoader".
I recommend you to use Android-Universal-Image-Loader for asynchronous image loading, caching and displaying.
来源：https://stackoverflow.com/questions/15586977/listview-scroll-lagging-when-images-is-shown