Develop Reference

RecyclerView using DiffUtil, prevent to scroll bottom on change

I have a problem with my recyclerViev, specifically with the scrolling.
I have some list, which is updated in real time, some item is added, some removed, and everything is sorted by some parameter.
So the item which was initially first on the list, can have its parameter changed, which will be in different position after the sorting.
So my recyclerView is for example focusing on the initial item, and after change, when some item has "better" parameter is changing position with that initial item.
Problem is, i want to focus on the new item, with "better" parameter when I'm not scrolling, but i don't want to focusing on it when i scroll by touch(so my touch will not be interrupted by scrolling to current first item on the list).
So i don't want to force this code after every change in my recyclerView data:
recyclerView.scrollToPosition(0);
because as i said, i will be interrupted by this scroll when i am touching my recyclerView list and go down to see other items and in the same time there will be a change in my list.
Is there a way to accomplish this?
To be specific, i am using DiffCallback from the DiffUtil, to support animations when there is a change in my current recyclerView list - it compares the old list with another new list and apply all the wanted animations and notifications(item added, removed, changed position). So i never call
notifyDataSetChanged
or anything like that
Here is my DiffUtil callback:
public static class DevicesDiffCallback extends DiffUtil.Callback{
List<DeviceInfo> oldDevices;
List<DeviceInfo> newDevices;
public DevicesDiffCallback(List<NexoDeviceInfo> newDevices, List<NexoDeviceInfo> oldDevices) {
this.newDevices = newDevices;
this.oldDevices = oldDevices;
}
#Override
public int getOldListSize() {
return oldDevices != null ? oldDevices.size() : 0;
}
#Override
public int getNewListSize() {
return newDevices != null ? newDevices.size() : 0;
}
#Override
public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
return oldDevices.get(oldItemPosition).getNexoIdentifier().getSerialNumber().equals(newDevices.get(newItemPosition).getNexoIdentifier().getSerialNumber());
}
#Override
public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
return oldDevices.get(oldItemPosition).equals(newDevices.get(newItemPosition));
}
#Override
public Object getChangePayload(int oldItemPosition, int newItemPosition) {
return super.getChangePayload(oldItemPosition, newItemPosition);
}
}
And i set it like this in my adapter, when i get the list of new data to be populated and replace the old data:
public void setData(List<DeviceInfo> data) {
DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(new DevicesDiffCallback(this.mData, data), false);
diffResult.dispatchUpdatesTo(this);
mData = data;
}

I'm not sure about this answer but, I think your code to call DiffUtil is not proper. Try using this :
public void addItems(List<Recipe> recipeList) {
List<Recipe> newRecipeList = new ArrayList<>();
newRecipeList.addAll(this.recipeList);
newRecipeList.addAll(recipeList);
DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(new RecipeDiffUtilCallback(this.recipeList, newRecipeList));
this.recipeList.addAll(recipeList);
diffResult.dispatchUpdatesTo(this);
}

Picasso + RecycleView insert image in wrong view

I have a simple adapter
public class ConversationListAdapter extends
RecyclerView.Adapter<Conversation.ViewHolder> {
private List<Conversation> items;
private Activity activity;
public ConversationListAdapter(Activity activity, List<Conversation> items) {
super();
this. items = items;
this.activity = activity;
}
#Override
public void onBindViewHolder(ViewHolder viewHolder, int i) {
Conversation conversation = mItems.get(i);
viewHolder.name.setText(conversation.getName());
if ( conversation.getUrl() != null) {
Picasso.with(activity.getApplicationContext()).load(conversation.getUrl())
.into(viewHolder.imageView);
}
}
and a basic
class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {..}
}
Now in the fragment as always:
mRecyclerView.setAdapter(new ConversationAdapter(getActivity(), mItems));
Now Im calling my rest api to get the data and the first time it works great everything is where it should be (let's say in c there is only 2 items and the order is conv1 and conv2)
private void handleResult(List<Conversation> c) {
items.clear()
items.addAll(c)
adapter.notifyDataSetChanged()
}
But... now if I refresh for example and the data in the List comes in a different order (conv2 and then conv1) after the adapter.notifyDataSetChanged() both of my imageView in the list have the same pictures.. ! But the textView however has the right text
This only happens with view filled with Picasso and cannot understand why
Could someone help me on this ?

you use if condition in any adapter you also have to set else part of it. i also don't know exactly why this is happen that if condition is given it takes same condition for child which are not match this, may be a bug in android. please try else part of it also. may be this work for you.

You have to replace your items in your adapter or create a new adapter with the new items
1st solution:
private void handleResult(List<Conversation> c) {
mRecyclerView.setAdapter(new ConversationAdapter(getActivity(), c));
}
2nd solution:
private void handleResult(List<Conversation> c) {
adapter.setList(c);
adapter.notifyDataSetChanged();
}
And don't to forget to create setList(List<Conversation> c) method in your Adapter

Android add/replace Items within RecyclerView

I know there are lots of threads already on this topic, but none of the given solutions worked for me so far. I'm trying to add or update an item of a RecyclerView. Here's my code so far:
MainActivity
private MyListItemAdapter mAdapter;
private RecyclerView recyclerView;
// called on activity create
private void init() {
// initialize activity, load items, etc ...
mAdapter = new MyListItemAdapter(this, items);
recyclerView.setAdapter(mAdapter);
}
// called when I want to replace an item
private void updateItem(final Item newItem, final int pos) {
mAdapter.replaceItem(newItem, pos);
}
MyListItemAdapter
public class MyListItemAdapter extends RecyclerView.Adapter<MyListItemAdapter.MyListItemViewHolder> {
private List<Item> mItems;
public void replaceItem(final Item newItem, final int pos) {
mItems.remove(position);
mItems.add(position, newItem);
notifyItemChanged(position);
notifyDataSetChanged();
}
}
I tried to make this changes from the MainActivity aswell, but in every case I tried my list doesn't get updated. The only way it worked was when I reset the adapter to the recyclerView:
mAdapter.notifyDataSetChanged();
recyclerView.setAdapter(mAdapter);
which obviously is a bad idea. (aside from the bad side effects wouldn't even work when I'm using lazy loading on my lists).
So my question is, how can I make notifyDataSetChanged() work properly?
edit
I found a solution for replacing items. After mAdapter.replaceItem(newItem, pos); I had to call recyclerView.removeViewAt(position);
This works for replacing an item, but doesn't solve my problem when I want to add items (e.g. lazy loading) to my list
edit2
I found a working solution for adding items
Adapter:
public void addItem(final Item newItem) {
mItems.add(newItem);
notifyDataSetChanged();
}
Activity:
private void addItem(final Item newItem) {
mAdapter.addItem(newItem);
recyclerView.removeViewAt(0); // without this line nothing happens
}
For some reason this works (also: it doesn't remove the view at position 0), but I'm sure this isn't the correct way to add items to a recyclerView

This should work:
private ArrayList<Item> mItems;
public void replaceItem(final Item newItem, final int position) {
mItems.set(position, newItem);
notifyItemChanged(position);
}
ArrayList.set() is the way to go to replace items.
For adding items, just append them to mItems and then go notifyDatasetChanged(). Another way to go is to use notifyItemRangeInserted(). Depending on where/how are you adding new items and how many of them, it might be worth it.

Use
mItems.set(position, newItem);
instead of
mItems.add(position, newItem);
because .set method will replace your data to particular position.

Undesired onItemSelected calls

I have 36 spinners that I have initialized with some values. I have used onItemSelectedListener with them. As usual, the user can interact with these spinners, firing the onItemSeected function.
One problem is that the call is made during init, but I found solutions to it here and avoided that using a global variable "count" and checking if count > 36 before executing code inside onItemSelected.
My problem is this:
The user has the option to click on a button called "Previous", upon which I have to reset SOME of the spinner values.
I tried changing the value of count to 0 before resetting the spinners, and then changing it back to 37 after resetting, but I have come to understand that the onItemSelected is called only after every other function is done executing, so it is called AFTER count is changed back to 37 even though the spinner values are set as soon as they are selected by user.
I need to repeatedly refresh some spinners WITHOUT firing off the onItemSelected function. Can anyone please help me find a solution? Thanks.

I found a simple and, I think, elegant solution.
Using tags.
I first created a new XML file called 'tags' and put in the following code:
<resources xmlns:android="http://schemas.android.com/apk/res/android">
<item name="pos" type="id" />
</resources>
Whenever I myself use spin.setSelection(pos), I also do spin.setTag(R.id.pos, pos), so I am setting the current position as a tag.
Then, in onItemSelected, I am executing code only if(spin.getTag(R.id.pos) != position), where position is the position variable supplied by the function.
In this way, my code is executed only when the user is making a selection.
Since the user has made a selection, the tag has not been updated, so after the processing is done, I update the tag as spin.setTag(R.id.pos, position).
NOTE: It is important to use the same adapter throughout, or the "position" variable might point to different elements.
EDIT: As kaciula pointed out, if you're not using multiple tags, you can use the simpler version, that is spin.setTag(pos) and spin.getTag() WITHOUT the need for an XML file.

When Spinner.setSelection(position) is used, it always activates setOnItemSelectedListener()
To avoid firing the code twice I use this solution:
private Boolean mIsSpinnerFirstCall = true;
...
Spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
//If a new value is selected (avoid activating on setSelection())
if(!mIsSpinnerFirstCall) {
// Your code goes gere
}
mIsSpinnerFirstCall = false;
}
public void onNothingSelected(AdapterView<?> arg0) {
}
});

I don't know if this solution is as foolproof as the chosen one here, but it works well for me and seems even simpler:
boolean executeOnItemSelected = false;
spinner.setSelection(pos)
And then in the OnItemSelectedListener
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
if(executeOnItemSelected){
//Perform desired action
} else {
executeOnItemSelected = true;
}
}

The way I solved this is by saving the OnItemSelectedListener first. Then set the OnItemSelectedListener of the Spinner to the null value. After setting the item in the Spinner by code, restore the OnItemSelectedListener again. This worked for me.
See code below:
// disable the onItemClickListener before changing the selection by code. Set it back again afterwards
AdapterView.OnItemSelectedListener onItemSelectedListener = historyPeriodSpinner.getOnItemSelectedListener();
historyPeriodSpinner.setOnItemSelectedListener(null);
historyPeriodSpinner.setSelection(0);
historyPeriodSpinner.setOnItemSelectedListener(onItemSelectedListener);

Here's my solution to this problem. I extend AppCompatSpinner and add a method pgmSetSelection(int pos) that allows programmatic selection setting without triggering a selection callback. I've coded this with RxJava so that the selection events are delivered via an Observable.
package com.controlj.view;
import android.content.Context;
import android.util.AttributeSet;
import android.view.View;
import android.widget.AdapterView;
import io.reactivex.Observable;
/**
* Created by clyde on 22/11/17.
*/
public class FilteredSpinner extends android.support.v7.widget.AppCompatSpinner {
private int lastSelection = INVALID_POSITION;
public void pgmSetSelection(int i) {
lastSelection = i;
setSelection(i);
}
/**
* Observe item selections within this spinner. Events will not be delivered if they were triggered
* by a call to setSelection(). Selection of nothing will return an event equal to INVALID_POSITION
*
* #return an Observable delivering selection events
*/
public Observable<Integer> observeSelections() {
return Observable.create(emitter -> {
setOnItemSelectedListener(new OnItemSelectedListener() {
#Override
public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
if(i != lastSelection) {
lastSelection = i;
emitter.onNext(i);
}
}
#Override
public void onNothingSelected(AdapterView<?> adapterView) {
onItemSelected(adapterView, null, INVALID_POSITION, 0);
}
});
});
}
public FilteredSpinner(Context context) {
super(context);
}
public FilteredSpinner(Context context, int mode) {
super(context, mode);
}
public FilteredSpinner(Context context, AttributeSet attrs) {
super(context, attrs);
}
public FilteredSpinner(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
public FilteredSpinner(Context context, AttributeSet attrs, int defStyleAttr, int mode) {
super(context, attrs, defStyleAttr, mode);
}
}
An example of its usage, called in onCreateView() in a Fragment for example:
mySpinner = view.findViewById(R.id.history);
mySpinner.observeSelections()
.subscribe(this::setSelection);
where setSelection() is a method in the enclosing view that looks like this, and which is called both from user selection events via the Observable and also elsewhere programmatically, so the logic for handling selections is common to both selection methods.
private void setSelection(int position) {
if(adapter.isEmpty())
position = INVALID_POSITION;
else if(position >= adapter.getCount())
position = adapter.getCount() - 1;
MyData result = null;
mySpinner.pgmSetSelection(position);
if(position != INVALID_POSITION) {
result = adapter.getItem(position);
}
display(result); // show the selected item somewhere
}

ListView not refreshing already-visible items

I'm displaying a list of contacts (name + picture) using the ListView. In order to make the initial load fast, I only load the names first, and defer picture loading. Now, whenever my background thread finishes loading a picture, it schedules my adapter's notifyDataSetChanged() to be called on the UI thread. Unfortunately, when this happens the ListView does not re-render (i.e. call getView() for) the items that are already on-screen. Because of this, the user doesn't see the newly-loaded picture, unless they scroll away and back to the same set of items, so that the views get recycled. Some relevant bits of code:
private final Map<Long, Bitmap> avatars = new HashMap<Long, Bitmap>();
// this is called *on the UI thread* by the background thread
#Override
public void onAvatarLoaded(long contactId, Bitmap avatar) {
avatars.put(requestCode, avatar);
notifyDataSetChanged();
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
// snip...
final Bitmap avatar = avatars.get(contact.id);
if (avatar != null) {
tag.avatar.setImageBitmap(avatar);
tag.avatar.setVisibility(View.VISIBLE);
tag.defaultAvatar.setVisibility(View.GONE);
} else {
tag.avatar.setVisibility(View.GONE);
tag.defaultAvatar.setVisibility(View.VISIBLE);
if (!avatars.containsKey(contact.id)) {
avatars.put(contact.id, null);
// schedule the picture to be loaded
avatarLoader.addContact(contact.id, contact.id);
}
}
}
AFAICT, if you assume that notifyDataSetChanged() causes the on-screen items to be re-created, my code is correct. However, it seems that is not true, or maybe I'm missing something. How can I make this work smoothly?

Here I go answering my own question with a hackaround that I've settled on. Apparently, notifyDataSetChanged() is only to be used if you are adding / removing items. If you are updating information about items that are already displayed, you might end up with visible items not updating their visual appearance (getView() not being called on your adapter).
Furthermore, calling invalidateViews() on the ListView doesn't seem to work as advertised. I still get the same glitchy behavior with getView() not being called to update on-screen items.
At first I thought the issue was caused by the frequency at which I called notifyDataSetChanged() / invalidateViews() (very fast, due to updates coming from different sources). So I've tried throttling calls to these methods, but still to no avail.
I'm still not 100% sure this is the platform's fault, but the fact that my hackaround works seems to suggest so. So, without further ado, my hackaround consists in extending the ListView to refresh visible items. Note that this only works if you're properly using the convertView in your adapter and never returning a new View when a convertView was passed. For obvious reasons:
public class ProperListView extends ListView {
private static final String TAG = ProperListView.class.getName();
#SuppressWarnings("unused")
public ProperListView(Context context) {
super(context);
}
#SuppressWarnings("unused")
public ProperListView(Context context, AttributeSet attrs) {
super(context, attrs);
}
#SuppressWarnings("unused")
public ProperListView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
class AdapterDataSetObserver extends DataSetObserver {
#Override
public void onChanged() {
super.onChanged();
refreshVisibleViews();
}
#Override
public void onInvalidated() {
super.onInvalidated();
refreshVisibleViews();
}
}
private DataSetObserver mDataSetObserver = new AdapterDataSetObserver();
private Adapter mAdapter;
#Override
public void setAdapter(ListAdapter adapter) {
super.setAdapter(adapter);
if (mAdapter != null) {
mAdapter.unregisterDataSetObserver(mDataSetObserver);
}
mAdapter = adapter;
mAdapter.registerDataSetObserver(mDataSetObserver);
}
void refreshVisibleViews() {
if (mAdapter != null) {
for (int i = getFirstVisiblePosition(); i <= getLastVisiblePosition(); i ++) {
final int dataPosition = i - getHeaderViewsCount();
final int childPosition = i - getFirstVisiblePosition();
if (dataPosition >= 0 && dataPosition < mAdapter.getCount()
&& getChildAt(childPosition) != null) {
Log.v(TAG, "Refreshing view (data=" + dataPosition + ",child=" + childPosition + ")");
mAdapter.getView(dataPosition, getChildAt(childPosition), this);
}
}
}
}
}

Add the following line to onResume()
listview.setAdapter(listview.getAdapter());

According to the documentation:
void notifyDataSetChanged ()
Notify any registered observers that the data set has changed.
... LayoutManagers will be forced to fully rebind and relayout all visible views...
In my case, the items were not visible (then whole RecycleView was outside the screen), and later on when it animated in, the item views didn't refresh either (thus showing the old data).
Workaround in the Adapter class:
public void notifyDataSetChanged_fix() {
// unfortunately notifyDataSetChange is declared final, so cannot be overridden.
super.notifyDataSetChanged();
for (int i = getItemCount()-1; i>=0; i--) notifyItemChanged(i);
}
Replaced all calls of notifyDataSetChanged() to notifyDataSetChanged_fix() and my RecyclerView happily refreshing ever since...