I'm using a custom list view adapter with a) view recycling and b) a view holder object.
I also successfully implemented an asynchronous image loader class to load bit maps to the list view for a smoother scrolling experience.
The problem now looks like the recycling, and correct if I'm wrong, but from a visual stand point it looks like the recycling is displaying previously loaded bit maps before the new ones are loaded such that there is a brief but noticeable flicker between the old image being replaced by the new one.
I hadn't noticed this effect before with the text views. Is this a recycling problem? Is there a way to scrape the old bit maps when the list item exits the visible screen area?
And yes, I am aware there are 3rd party libraries that account for all these effects. If I can't solve this problem by hand, then I will look into a library.
This is my list adapter
// Get the data item for this position
SongObject songObject = list.get(position);
// view lookup cache stored in tag
ViewHolder viewHolder;
// Check if an existing view is being reused, otherwise inflate the view
if (convertView == null) {
viewHolder = new ViewHolder();
LayoutInflater inflater = LayoutInflater.from(getContext());
convertView = inflater.inflate(R.layout.list_view_item, parent, false);
convertView.setTag(viewHolder);
} else {
viewHolder = (ViewHolder) convertView.getTag();
}
// Set view holder references
viewHolder.album = (TextView) convertView.findViewById(R.id.album);
viewHolder.artist = (TextView) convertView.findViewById(R.id.artist);
viewHolder.title = (TextView) convertView.findViewById(R.id.title);
viewHolder.albumArt = (ImageView) convertView.findViewById(R.id.album_art);
viewHolder.duration = (TextView) convertView.findViewById(R.id.duration);
// Set values to referenced view objects
viewHolder.album.setText(songObject.album);
viewHolder.artist.setText(songObject.artist);
viewHolder.title.setText(songObject.title);
viewHolder.duration.setText(FormatTime(songObject.duration));
// Load album art asynchronously for smoother scrolling experience
new ImageLoader(viewHolder.albumArt).execute(songObject.albumArtURI);
// Return the converted view
return convertView;
Do you use recyclerView? Can you add code of recyclerViewAdapter implementation?
onBindViewHolder is a place where you should 'tune' you previously used (or not used) viewHolder before giving it to user
Related
I'm new to android programming, and I've been reading a lot about it lately. One of the features of ListView, if I understood it right, is that it recycle views and just replaces it with new data when an item is off the screen.
And just a few minutes ago, I was reading up about endless scrolling, and RecyclerView has been one of the popular choices to implement such a feature. So I looked up RecyclerView, and in this video, it is mentioned that RecyclerView recycles a view automatically to reuse it for new data (as a way to contrast its difference with ListView).
Did I misunderstand ListView about its recycling mechanism? Or if it does recycle, how do you actually implement (or how do you know you are implementing) it?
RecyclerView does recycling automatically. In order to make ListView recycle items you will need to do this modification inside of adapter class.
#Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
//brand new
convertView = LayoutInflater.from(mContext).inflate(R.layout.days_list_item, null);
holder = new ViewHolder();
// below is variables that will be different in your case
holder.numberOfDays = (TextView) convertView.findViewById(R.id.eventDays);
holder.sinceOrUntil = (TextView) convertView.findViewById(R.id.eventType);
holder.eventTitle = (TextView) convertView.findViewById(R.id.eventTitle);
holder.daysText = (TextView) convertView.findViewById(R.id.DaysText);
convertView.setTag(holder);
}
else {
//reusing item
holder = (ViewHolder) convertView.getTag();
}
// rest of the code
}
For more details refer to this link.
I have a ListView which multiple contains checkboxes for user input. I have two buttons add and remove to add and remove list items respectively.
I am using BaseAdapter for ListView and notifying the ListView using notifyDataSetChanged()
Anytime I add/remove the items. The user input in the list gets cleared. I think it's because the list is getting rebuilt everytime. Any ideas on how to keep the user input while add/remove the items in listView ?
in listview you have only one option is to use notifyDatasetChanged() with adapter. just dont clear your whole list just do add/remove and then notify adapter or use Recycclerview instead.
With recyclerview you have many options like notifyDataInserted, notifyDataRemoved, range inserted, range removed etc.
You can find a good example here
i think your programme is reading getView() function again. see the below code to avoid it, it is copy pasted but it may give you some idea-
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
convertView = mInflater.inflate(R.layout.list_item_icon_text, null);
holder = new ViewHolder();
holder.text = (TextView) convertView.findViewById(R.id.text);
holder.icon = (ImageView) convertView.findViewById(R.id.icon);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
holder.text.setText(DATA[position]);
holder.icon.setImageBitmap((position & 1) == 1 ? mIcon1 : mIcon2);
return convertView;
}
you can refer this link for more info-0
Android, how to stop reading getView() function again, if the content is already downloaded in the ListView
We are working with list views in college at the moment. My lecturer gave us a simple application that displays mail messages in a list and when the user selects one it displays the content of the message in a new activity. I understand pretty much all of what is going on but there are a few grey areas I want to clear up!
Basically I am wondering what this section of code does?
#Override
public View getView(final int position, View convertView, ViewGroup parent) {
View v = convertView;
if (v == null) {
LayoutInflater vi = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
v = vi.inflate(R.layout.inbox_row, null);
}
This method is located within a class that extends ArrayAdapter. Am I right in thinking that it is some form of recycling? for when views go on and off the screen?....
Any help is much appreciated. thanks.
it's exactly what you said, a form of recycling.
Inflating a layout takes a lot of memory and a lot of time, so for the efficiency sake, the system passes to you that just went off the screen and you can simply update its text and images and give them back to the UI.
So for example, if your list view is showing 6 items on its list (due to the height of it), it will only inflate 6 items and during scroll it just keeps recycling them.
there's some extra optimisations tricks that you should use and I'm sure that the video link that the commenter posted will explain them.
edit
that example is an ArrayAdapter of Store items, but you can make it to whatever you need.
the adapter does the match and separation layer between UI and data.
#Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null)
convertView = newView();
// Store is the type of this ArrayAdapter
Store store = getItem(position);
Holder h = (Holder) convertView.getTag();
// And here I get the data and address them to the UI
// as you can see, if the convertView is not null,
// I'm not creating a new one, I'm just changing text, images, etc
h.storeName.setText(store.getStoreName());
h.address.setText(store.getAddressLine1());
h.postcode.setText(store.getPostCode());
h.distance.setText(store.getDistance());
return convertView;
}
// I like to separate in a different method when the convertView is null
// but that's me being organisation obsessive
// but it also makes easy to see which methods are only being called the 1st time
private View newView() {
LayoutInflater inf = LayoutInflater.from(getContext());
View v = inf.inflate(R.layout.map_result_list, null);
Holder h = new Holder();
// here we store that holder inside the view itself
v.setTag(h);
// and only call those findById on this first start
h.storeName = (TextView) v.findViewById(R.id.txtLine1);
h.address = (TextView) v.findViewById(R.id.txtLine2);
h.postcode = (TextView) v.findViewById(R.id.txtLine3);
h.distance = (TextView) v.findViewById(R.id.txtDistance);
return v;
}
// this class is here just to hold reference to the UI elements
// findViewById is a lengthy operation so this is one of the optimisations
private class Holder {
TextView storeName;
TextView address;
TextView postcode;
TextView distance;
}
I have a list of items. Each of them has a set of data displayed with TextViews. This data remains mostly unchanged. But I have a distance field, which I would like to update whenever I get new lock from location provider.
The question is: Should I just update my data and call notifyDataSetChanged() on my Adapter or is there a more efficient way?
Seems very expensive to reload all the lists (I have several of them in a ViewPager) just because one TextView in each list item needs to be updated.
Here is my getView() from my adapter. It might help:
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
convertView = mInflater.inflate(R.layout.eventrow, parent, false);
// Creates a ViewHolder and store references to the two children views
// we want to bind data to.
holder = new ViewHolder();
holder.title = (TextView) convertView.findViewById(R.id.eventTitle);
holder.distance = (TextView) convertView.findViewById(R.id.eventDistance);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
holder.title.setText(((EventItem) getItem(position)).getTitle());
holder.distance.setText(String.valueOf(((EventItem) getItem(position)).getDistance()));
return convertView;
}
I also thought about directly referencing the holder.distance but it seems like a bad idea to do it outside getView().
The correct way to modify your data is to change your list item and then call notifyDataSetChanged().
The only alternative that comes to my mind is to set again the adapter on the list view which is way more expensive. There are no other ways.
So the answer is: you HAVE to go through notifyDataSetChanged().
I have a straight forward BaseAdapter for my ListView. It downloads a JSON feed and displays the data in the rows. There is a ViewHolder which contains the views and a data object called "Story". Everything works just fine.
However, after some scrolling of longer lists, I notice two things.
1) My log shows that the adapter is reloading the feed when scrolling further down. This is strange, as I put the whole JSON array into a variable, so why does it have to reload?
2) More importantly, after some scrolling back and forth, the rows contain the wrong "Story" objects. Here are the relevant parts of the getView routine:
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
Story story = stories.get(position);
if (convertView == null) {
//create holder
holder = new ViewHolder();
convertView = inflator.inflate(R.layout.story_list_item, parent, false);
holder.titleView = (TextView) convertView.findViewById(R.id.story_list_title);
holder.dateView = (TextView) convertView.findViewById(R.id.story_list_date);
holder.story = story;
holder.imageView = (ImageView) convertView.findViewById(R.id.story_list_image);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
// configure the view
holder.titleView.setText(story.title);
return convertView;
}
Simple enough. Now the strange thing is that I can fix the problem by eliminating the if statement if (convertView == null) (and, I presume, eliminating the row recycling as well).
But will I not run into memory problems this way? Why does the plain vanilla version not work?
Thanks for your help.
Regards,
S
You are aware that you're only assigning
holder.story = story
when convertView == null ? Consider moving holder.story = story to just after your convertView if-case and it should work a lot better. Btw, do you even need to store the "story" inside your view holder? Typically that pattern should only be used to store Views and view state information, not the data of the actual position.