Develop Reference

Two items get selected in listview android

I'm trying to implement a custom listview. Everything works fine until I use a if () statement inside the getView() method
Without the if() condition a single item gets selected when I select an item but when I add the if() condition, the views are displayed properly but two items (non-adjacent) get selected (1st and last 1st or and second-last, any such combination).
View getView(...){
....
if (!item.getPriceTo().equals(""))
priceToTV.setText(item.getPriceTo());
else
priceToTV.setText(item.getPriceFrom());
return view;
}
Also I'm using saving the previous view to show the selection so the current selection has a red_border and when it is selected a black_border is set to it.:
subItemsListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
Log.d("New Order", "........");
if (previousViewOfSubItems != null && previousViewOfSubItems != view) {
previousViewOfSubItems.setBackgroundResource(R.drawable.black_border);
if (quantity.getText().toString().equals("xx") || quantity.getText().toString().equals("0")) {
viewForVisibility.setVisibility(View.GONE);
layoutForQuantity.setVisibility(View.GONE);
}
}
if (previousViewOfSubItems == view)
return;
previousViewOfSubItems = view;
previousViewOfSubItems.setBackgroundResource(R.drawable.red_border);
viewForVisibility = previousViewOfSubItems.findViewById(R.id.viewForVisibility);
viewForVisibility.setVisibility(View.VISIBLE);
layoutForQuantity = (LinearLayout) previousViewOfSubItems.findViewById(R.id.layoutForQuantity);
layoutForQuantity.setVisibility(View.VISIBLE);
quantity = (TextView) previousViewOfSubItems.findViewById(R.id.subTypeQuantity);
}
});

previousViewOfSubItems = view; seems to be causing the problem,
In Listviews with adapter you should avoid saving view instances, because views are reused by adapters so view can be same for two rows so rather than saving view instance's reference use ViewHolder Design pattern and use view tagging

You need to use ViewHolder Pattern and view tagging to properly identify every view in different position. ListView always recycle the view instead of re-inflating the view again and again.
You can refer to Android Training documentation on how to implement ViewHolder pattern.

ListViews recycle the views in the list. so as you scroll, top views are reused and content replaced using the methods.
Where you set background to Red etc, use Else statements to set it back to your default black.

its beacause it listview reuses view to display items, once the first view is scrolled out the the same view is reused to display the view at bottom of the listview. instead of comparing the view try compairing the position of the view clicked

I have explained about this abnormal behavior in my blog on recyclerview you refer that to solve this problem.
use pojo class to get the status and update the view accordingly

ListView and it's "weird" behavior. How can i solve this situation?

As you should know, ListView recycles the view. But i want to work with elements that can be clicked and expanded. Like i already did:
But it was completely messed up, even using:
View checklayout = convertView;
if(checklayout == null){
checklayout = inflater.inflate(R.layout.home_cell, null);
}
When some opened expandable views goes out of the screen, the recycled one, which shouldn't be expandable, receives the vanished's layout. Only view that has "1 AVALIAÇÃO LANÇADA" should open, and show it's content. I add this content by using if(qtdAvaliacoes > 0) that is a property of my Object that comes from ArrayList<>.
I "solved" this disabling the recycler, with:
#Override
public int getViewTypeCount() {
return getCount();
}
#Override
public int getItemViewType(int position) {
return position;
}
Once my listView will only receives 5~10 rows. But i know that isn't a good practice. While i'm writting this question, i found a solution, calling my object before inflate any view, then checking the property:
#Override
public View getView(int position, View convertView, ViewGroup parent) {
View checklayout = convertView;
final LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
final Disciplina disciplina = lista.get(position);
if(checklayout == null || disciplina.getQtdAvaliacoes() == 0){
checklayout = inflater.inflate(R.layout.home_cell, null);
}
final View layout = checklayout;
But I don't think this is the best way to do this. I read something about Tags, but was little confused. I think if i could bind these onClick methods to the row position it would be better.
Any ideas ? Or is my solution good at you, developer's, point of view.
Thanks.

The easiest way is to not do subinflates within a list item. Do it via view visibilities instead, making the inflated part GONE if you don't want it to display yet. You'll just have to explicitly set the visibility of that view in every call to getView

ListView onItemClick not called

I've seen all the related questions, and tried their answers. I have a ListView inside a fragment and it's onItemClick method is called when inside one activity, but not called when in another one. Everything else is the same. I've tried:
Changing android:clickable explicitly.
Changing android:focusable and android:focusableInTouchMode explicitly.
Calling listView.setItemsCanFocus.
Adding android:descendantFocusability="blocksDescendants" attribute both on fragment and activity root.
Still, it's not working. It's the same fragment with same adapter, which doesn't have conditionals about being in which activity. However, in one activity it works perfectly, and in another, onItemClick is not called. I'm on ICS. Why would this happen?
UPDATE:
Here is the relevant code in my fragment:
dataSource = (ArrayList<Map<String, Object>>) task.getResult();
FeedAdapter adapter = new FeedAdapter(getActivity(), dataSource, getUser());
ListView list = (ListView) rootView.findViewById(R.id.listView);
list.setItemsCanFocus(true);
 //just trying these
list.setOnItemClickListener(self);
list.setAdapter(adapter);
adapter.notifyDataSetChanged();
if (dataSource.size() == 0) {
noPostsLabel.setVisibility(View.VISIBLE);
}
And in my adapter:
public View getView(int position, View convertView, ViewGroup parent) {
View view;
final Map<String, Object> post = objects.get(position);
LayoutInflater inflater = LayoutInflater.from(getContext());
if (convertView == null || convertView.getId() == R.id.headerRoot) {
view = inflater.inflate(R.layout.list_item_post_layout, parent, false);
} else {
view = convertView;
}
view.setClickable(false); //just trying these two now, they weren't here originally
view.setFocusable(false);
//populate
view.setTag(post);
[...] //populate the cell. very long code, redacted.
return view;
}
UPDATE 2:
I've also realized some cells are also not selectable in my "working" activity too, when they have a visible HorizontalScrollView within the cell (I have file attaching feature and it's only visible when there are files. Otherwise, it's in GONE visibility state). I have no idea why it's causing such trouble.
UPDATE 3:
I've also found out that views inside the cell are responsive. It's just the cell view itself which is not taking input.
UPDATE 4:
I've ended up moving the tap handler logic to the cell layout itself, instead of relying on list view's handler. I know it's not a good practice but I had to meet a deadline. Besides, it's working pretty smooth now. I'm not closing/answering the question as the technical problem is still present and I haven't found a real solution to it. I've just used a workaround to meet my project deadline.

I am not sure of your problem and I don't see the full code to debug.
I'll submit a sample code which normally should work in a Fragment.
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
ListView list = (ListView) view.findViewById(R.id.listView);
list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int positi on, long id) {
Log.d(TAG, "onItemClick");
}
});
Notes:
I don't use root or any other cached object. I use the view parameter for calling findViewById().
I don't know self also. Instead I instantiated a new view or AdapterView.

Have you tried setting callbacks for the fragments? That's the way Android recommends it. You can check out - https://developer.android.com/training/basics/fragments/communicating.html#Deliver

Issue when fast scroll a listview

I am working on a small project where I create a listview bound to an ArrayAdapter. In the getView() function of ArrayAdapter, I do a loading of images from web urls on thread, and set them to list items (based on position of course, so url[0] image is set to list_item[0] etc). It all seems to work well.
However when I was testing the app, I noticed that if I wait my listview to fully display, then perform a fast scroll back and forth, I see sometimes the image on one list item is misplaced on other (like being in an intermediate state). However it's not going away until I scroll the wrongly-displayed-item out of screen and then back.
I do not know if it relates to my loading web url using thread, or maybe loading image from local resource folder can have the same issue.
This actually leads to a question I have about getView() function. I think the logic is correct in my getView() because it's as simple as a binding of url to view based on position. And whenever getView() get a chance to be called, like when I scroll an item out of screen then back, it will make the list item display correctly.
The thing I do not understand is how to explain the issue that happened (like an intermediate state), and how to avoid it when writing code?
I paste my adapter code piece below, but I think the question maybe a general one:
#Override
public View getView(int position, View v, ViewGroup parent) {
ViewHolder viewHolder = null;
if (v == null) {
LayoutInflater inflater = (LayoutInflater) getContext()
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
v = inflater.inflate(layoutResourceId, parent, false);
viewHolder = new ViewHolder();
viewHolder.title = (TextView) v.findViewById(R.id.title);
viewHolder.description = (TextView) v.findViewById(R.id.description);
viewHolder.image = (ImageView) v.findViewById(R.id.image);
v.setTag(viewHolder);
} else {
viewHolder = (ViewHolder) v.getTag();
}
listItem item = items[position]; //items is some global array
//passed in to ArrayAdapter constructor
if (item != null) {
viewHolder.title.setText(item.title);
viewHolder.description.setText(item.description);
if (!(item.imageHref).equalsIgnoreCase("null")) {
mDrawableManager.fetchDrawableOnThread(item.imageHref, viewHolder.image);
} else {
viewHolder.image.setImageDrawable(null);
}
}
return v;
}
}
static class ViewHolder {
TextView title;
TextView description;
ImageView image;
}

I have same issue when scroll quickly it alternate the vales of some item to others, just like background color of some items if changes randomly. I solved this issue by searching a lot and find exact solution is just adding these two methods in your adapter if you are using ViewHolder in your adapter
#Override
public int getViewTypeCount() {
return getCount();
}
#Override
public int getItemViewType(int position) {
return position;
}

Assuming that you are not caching the downloaded image.. lets see the following code:
if (!(item.imageHref).equalsIgnoreCase("null")) {
mDrawableManager.fetchDrawableOnThread(item.imageHref, viewHolder.image);
} else {
viewHolder.image.setImageDrawable(null);
}
Now if the image view is getting reused then it would already have the old image for the assigned list item. So until the thread download the image from the network it would display the old image and when the thread download the image for the current item it would be replaced with the new image. Try to change it to:
if (!(item.imageHref).equalsIgnoreCase("null")) {
viewHolder.image.setImageDrawable(SOME_DEFULAT_IMAGE);
mDrawableManager.fetchDrawableOnThread(item.imageHref, viewHolder.image);
} else {
viewHolder.image.setImageDrawable(null);
}
Or you can use something link smart image view that supports HTTP URI and also caches the images. Check out following link for smart image view:
https://github.com/loopj/android-smart-image-view
http://loopj.com/android-smart-image-view/

Add ImageLoader class from below link in your project.
link
just call DisplayImage() methode of Image loader class as below in getView()
ImageLoader imageLoader = new ImageLoader();
yourImageView.setTag(URL_FOR_Your_Image);
imageLoader.DisplayImage(URL_FOR_Your_Image,ACTIVITY.this, yourImageView);
Your images will load in background as you want without wait.

I think you should declare your downloader method fetchDrawableOnThread() as "synchronized" . Because a lot of threads are working simultaneously and any thread which started later, can end earlier. So there are chances of images being misplaced.
It happened to me for a long time. Finally "synchronized" helped me do it cleanly. I hope it helps you too.

I give it a try with synchronization again. Either synchronize the fetchDrawableOnThread(), or synchronize the global hashmap data within fetchDrawableOnThread(). First i thought the issue is gone, but when i tried more times later, i found the issue is still there.
Then i thought about the synchronization. fetchDrawableOnThread() is called from getView(), and getview() itself does not have a concurrency issue. Even if as Yogesh said, what happened INSIDE getView() is thread-based, and return early or late, it can not affect the correctness of getView(), i.e. the list item's display, only the sooner or later.
What i did(synchronization) inside fetchDrawableOnThread() i think it's still correct, 'cause i used a hashmap to cache images downloaded from remote url, and this hashmap is read/write upon in a multi-thread situation, so it should be locked. But i do not think it's the rootcause of the UI misplace, if hashmap is messed up, the image misplacement will be permanent.
Then i looked further on convertView reuse mechanism based on Praful's explanation. He explained clearly what happened when image always comes from remote and no cache locally, but my situation is i waited my list to display fully, i.e. all images download complete and cached complete, before i do the fast scroll. So in my experiment, the images are read from cache.
Then when inspecting my code, i saw one minor difference in the use of convertView as in getView() method, a lot of the example usages are like this:
public View getView(int position, View convertView, ViewGroup parent) { // case 1
View v = convertView;
.... // modify v
return v;
}
However the example i happened to copy from use:
public View getView(int position, View convertView, ViewGroup parent) { // case 2
.... // modify convertView
return convertView;
}
I thought it makes no difference at first, 'cause according to what android says, 'ListView sends the Adapter an old view that it's not used any more in the convertView param.', so why not use 'convertView' para directly?
But i guess i was wrong. I changed my getView() code to case 1. Boom! everything works. No funny business ever no matter how fast i scroll the list.
Quite strange, is convertView only old, or is it old & in-use? If the later, we should only get a copy and then modify..... ??

Problem setting row backgrounds in Android Listview

I have an application in which I'd like one row at a time to have a certain color. This seems to work about 95% of the time, but sometimes instead of having just one row with this color, it will allow multiple rows to have the color. Specifically, a row is set to have the "special" color when it is tapped. In rare instances, the last row tapped will retain the color despite a call to setBackgroundColor attempting to make it otherwise.
private OnItemClickListener mDirectoryListener = new OnItemClickListener(){
public void onItemClick(AdapterView parent, View view, int pos, long id){
if (stdir.getStationCount() == pos) {
stdir.moreStations();
return;
}
if (playingView != null)
playingView.setBackgroundColor(Color.DKGRAY);
view.setBackgroundColor(Color.MAGENTA);
playingView = view;
playStation(pos);
}
};
I have confirmed with print statements that the code setting the row to gray is always called.
Can anyone imagine a reason why this code might intermittently fail? If there is a pattern or condition that causes it, I can't tell.
I thought it might have something to do with the activity lifecycle setting the "playingView" variable back to null, but I can't reliably reproduce the problem by switching activities or locking the phone.
private class DirectoryAdapter extends ArrayAdapter {
private ArrayList<Station> items;
public DirectoryAdapter(Context c, int resLayoutId, ArrayList<Station> stations){
super(c, resLayoutId, stations);
this.items = stations;
}
public int getCount(){
return items.size() + 1;
}
public View getView(int position, View convertView, ViewGroup parent){
View v = convertView;
LayoutInflater vi = (LayoutInflater)getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (position == this.items.size()) {
v = vi.inflate(R.layout.morerow, null);
return v;
}
Station station = this.items.get(position);
v = vi.inflate(R.layout.songrow, null);
if (station.playing)
v.setBackgroundColor(Color.MAGENTA);
else if (station.visited)
v.setBackgroundColor(Color.DKGRAY);
else
v.setBackgroundColor(Color.BLACK);
TextView title = (TextView)v.findViewById(R.id.title);
title.setText(station.name);
return v;
}
};

ListViews don't create instances of contained views for every item in the list, but only for ones that are actually visible on the screen. For performance reasons, they try and maintain as few views as possible, and recycle them. That's what the convertView parameter is.
When a view scrolls off the screen, it may be recycled or destroyed. You can't hold a reference to an old view and assume that it will refer to the item you expect it to in the future. You should save the ID of the list item you need and look that up instead.
Moreover, there are a couple of other issues with your implementation (from a best practices standpoint). You seem to be ignoring the convertView parameter and creating a new view from scratch each time. That can cause your application to bog down a bit while scrolling if you have a long list. Secondly, instead of adding the "more" element the way you do, you're better of setting it with setFooterView().
There's an excellent talk on the ListView from Google I/O 2010 that covers these and other issues. It's an hour long, but definitely worth watching in its entirety.