Develop Reference

Adding empty space between items of RecyclerView with GridLayoutManager

I want to add empty spaces between items of a RecyclerView with GridLayoutManager but I can't find anything which solves my problem.
I am creating a custom calendar and I have to make a custom grid from scratch. The first day of the month should be placed farther from the start when it is not the first day of the week.
I have achieved a similar result by passing a firstItemLocation to my RecyclerView adapter and overriding the onBindViewHolder method like this:
#Override
public void onBindViewHolder(#NonNull ViewHolder holder, int position) {
if (position < firstItemLocation) {
holder.itemView.setVisibility(View.GONE);
} else {
holder.tv.setText(String.format(Locale.US, "%d", list.get(position - firstItemLocation)));
}
}
It works fine but in a hypothetical situation when the user has to scroll it adds random empty spaces and glitches like this.
Any seggestions to make it better without that glitch?

read about "recycling pattern", how it works and why - RecyclerView got its name because of this, so its very important to understand how this works
but in short:
inside onBindViewHolder you have to call desired methods ALWAYS. you are calling setVisibility only inside if and not in else. try with bellow snippet
if (position < firstItemLocation) {
holder.itemView.setVisibility(View.GONE);
holder.tv.setText("")
} else {
holder.itemView.setVisibility(View.VISIBLE);
holder.tv.setText(String.format(Locale.US, "%d", list.get(position - firstItemLocation)));
}
thats because holder may be a "recycled" instance, used previously to draw another list item, and its set up is still applied to views

Added element doesn't show in RecyclerView after deleting another with swipe

Edit: if anyone is having the same problem in the future it was a pretty easy fix. I used clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) to handle when the entire drag was finished and had forgotten to call it's super-method. That's why it didn't update properly.
Original question:
Here's the entire code: https://github.com/vustav/Ppaaiinntt/tree/master/app/src/main/java/com/decent/rvtest
Everything works fine except when I add an element right after deleting another. It does exist though. If I add another there's a properly sized space between the old list and the new element. I use a string where they add their names before a print and it shows there, and if I drag to change positions of the elements it shows up properly.
My reputation doesn't allow me to post images so an imgur-album will have to do:
http://imgur.com/a/bmb17
On the first image there's three elements and the string is printed at the bottom.
The second image is after the swipe. Notice the string is updated.
The third is after adding another "111". The string is correct but it doesn't show up in the view.
The fourth is after adding another. The string is still correct and the new element shows up in the view.
The last image is after dragging to change the position of the last two elements. Now everything is fine again.
These are the relevant methods (I think):
protected void add(PictureElement pe){
chain.add(pe);
notifyItemInserted(chain.size()-1);
}
public void remove(int position) {
chain.remove(position);
notifyItemRemoved(position);
}
protected void swap(int from, int to){
chain.swap(from, to);
notifyItemMoved(from, to);
}
Edit: onBindViewHolder, getItemCount and the ViewHolder:
#Override
public int getItemCount() {
return chain.size();
}
#Override
public void onBindViewHolder(PEViewHolder PEViewHolder, int i) {
PictureElement pe = chain.get(i);
PEViewHolder.name.setText(pe.getName());
}
protected static class PEViewHolder extends RecyclerView.ViewHolder {
protected TextView name;
public PEViewHolder(View v) {
super(v);
name = (TextView) v.findViewById(R.id.txtName);
}
}

Interesting quote on the different notify methods you are using
public final void notifyItemRemoved (int position) Notify any registered observers that the item previously located at position has
been removed from the data set. The items previously located at and
after position may now be found at oldPosition - 1. This is a
structural change event. Representations of other existing items in
the data set are still considered up to date and will not be rebound,
though their positions may be altered. Parameters position : Position
of the item that has now been removed.
public final void notifyItemRangeChanged (int positionStart, int itemCount) Notify any registered observers that the itemCount items
starting at position positionStart have changed. Equivalent to calling
notifyItemRangeChanged(position, itemCount, null);. This is an item
change event, not a structural change event. It indicates that any
reflection of the data in the given position range is out of date and
should be updated. The items in the given range retain the same
identity.
Could you try and comment this block of code and check if it works
//Called by the ItemTouchHelper when the user interaction with an element is over and it also
// completed its animation
/*
#Override
public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
//update from where the action took place
mPEAdapter.updateChain(viewHolder.getLayoutPosition());
//clearView is called after onMove so any drags or swipes are complete
dragging = false;
mPEAdapter.setSwipe(false);
}
*/

onBindViewHolder() is never called on view at position even though RecyclerView.findViewHolderForAdapterPosition() returns null at that position

I have a list with 13 items (although items may be added or removed), positions 0-12. When the fragment containing the RecyclerView is first shown, only positions 0 through 7 are visible to the user (position 7 being only half visible). In my adapter I Log every time a view holder is binded/bound (idk if grammar applies here) and record its position.
Adapter
#Override
public void onBindViewHolder(final ViewHolder holder, final int position) {
Log.d(TAG, "onBindViewHolder() position: " + position);
...
}
From my Log I see that positions 0-7 are bound:
I have a selectAll() method that gets each ViewHolder by adapter position. If the returned holder is NOT null I use the returned holder to update the view to show it's selected. If the returned holder IS null I call selectOnBind() a method that flags the view at that position update to show it's selected when it's binded rather than in real time since it's not currently shown:
public void selectAll() {
for (int i = 0; i < numberOfItemsInList; i++) {
MyAdapter.ViewHolder holder = (MyAdapter.ViewHolder)
mRecyclerView.findViewHolderForAdapterPosition(i);
Log.d(TAG, "holder at position " + i + " is " + holder);
if (holder != null) {
select(holder);
} else {
selectOnBind(i);
}
}
}
In this method I Log the holder along with its position:
So up to this point everything seems normal. We have positions 0-7 showing, and according to the Log these are the positions bound. When I hit selectAll() without changing the visible views (scrolling) I see that positions 0-7 are defined and 8-12 are null. So far so good.
Here's where it gets interesting. If after calling selectAll() I scroll further down the list positions 8 and 9 do not show they are selected.
When checking the Log I see that it's because they are never bound even though they were reported to be null:
Even more confusing is that this does not happen every time. If I first launch the app and test this it may work. But it seems to happen without fail afterwards. I'm guessing it has something to do with the views being recycled, but even so wouldn't they have to be bound?
EDIT (6-29-16)
After an AndroidStudio update I cannot seem to reproduce the bug. It works as I expected it to, binding the null views. If this problem should resurface, I will return to this post.

This is happening because:
The views are not added to the recyclerview (getChildAt will not work and will return null for that position)
They are cached also (onBind will not be called)
Calling recyclerView.setItemViewCacheSize(0) will fix this "problem".
Because the default value is 2 (private static final int DEFAULT_CACHE_SIZE = 2; in RecyclerView.Recycler), you'll always get 2 views that will not call onBind but that aren't added to the recycler

In your case views for positions 8 and 9 are not being recycled, they are being detached from the window and will be attached again. And for these detached view onBindViewHolder is not called, only onViewAttachedToWindow is called. If you override these function in your adapter, you can see what I am talking.
#Override
public void onViewRecycled(ViewHolder vh){
Log.wtf(TAG,"onViewRecycled "+vh);
}
#Override
public void onViewDetachedFromWindow(ViewHolder viewHolder){
Log.wtf(TAG,"onViewDetachedFromWindow "+viewHolder);
}
Now in order to solve your problem you need to keep track of the views which were supposed to recycled but get detached and then do your section process on
#Override
public void onViewAttachedToWindow(ViewHolder viewHolder){
Log.wtf(TAG,"onViewAttachedToWindow "+viewHolder);
}

The answers by Pedro Oliveira and Zartha are great for understanding the problem, but I don't see any solutions I'm happy with.
I believe you have 2 good options depending on what you're doing:
Option 1
If you want onBindViewHolder() to get called for an off-screen view regardless if it's cached/detached or not, then you can do:
RecyclerView.ViewHolder view_holder = recycler_view.findViewHolderForAdapterPosition( some_position );
if ( view_holder != null )
{
//manipulate the attached view
}
else //view is either non-existant or detached waiting to be reattached
notifyItemChanged( some_position );
The idea is that if the view is cached/detached, then notifyItemChanged() will tell the adapter that view is invalid, which will result in onBindViewHolder() getting called.
Option 2
If you only want to execute a partial change (and not everything inside onBindViewHolder()), then inside of onBindViewHolder( ViewHolder view_holder, int position ), you need to store the position in the view_holder, and execute the change you want in onViewAttachedToWindow( ViewHolder view_holder ).
I recommend option 1 for simplicity unless your onBindViewHolder() is doing something intensive like messing with Bitmaps.

When you have large number of items in the list you have passed to recyclerview adapter you will not encounter the issue of onBindViewHolder() not executing while scrolling.
But if the list has less items(I have checked on list size 5) you may encounter this issue.
Better solution is to check list size.
Please find sample code below.
private void setupAdapter(){
if (list.size() <= 10){
recycler.setItemViewCacheSize(0);
}
recycler.setAdapter(adapter);
recycler.setLayoutManager(linearLayoutManager);
}

I think playing with view is not a good idea in recyclerview. The approach I always use to follow to just introduce a flag to the model using for RecyclerView. Let assume your model is like -
class MyModel{
String name;
int age;
}
If you are tracking the view is selected or not then introduce one boolean to the model. Now it will look like -
class MyModel{
String name;
int age;
boolean isSelected;
}
Now your check box will be selected/un-selected on the basis of the new flag isSelected (in onBindViewHolder() ). On every selection on view will change the value of corresponding model selected value to true, and on unselected change it to false. In your case just run a loop to change all model's isSelected value to true and then call notifyDataSetChanged().
For Example, let assume your list is
ArrayList<MyModel> recyclerList;
private void selectAll(){
for(MyModel myModel:recyclerList)
myModel.isSelected = true;
notifyDataSetChanged();
}
My suggestion, while using recyclerView or ListView to less try to play with views.
So in your case -
#Override
public void onBindViewHolder(final ViewHolder holder, final int position) {
holder.clickableView.setTag(position);
holder.selectableView.setTag(position);
holder.checkedView.setChecked(recyclerList.get(position).isSelected);
Log.d(TAG, "onBindViewHolder() position: " + position);
...
}
#Override
public void onClick(View view){
int position = (int)view.getTag();
recyclerList.get(position).isSelected = !recyclerList.get(position).isSelected;
}
#Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
int position = (int)buttonView.getTag();
recyclerList.get(position).isSelected = isChecked;
}
Hope it will help you, Please let me know if you need any further explanation :)

So I think you question is answered below by #Pedro Oliveira. The main sense of RecycleView, that he using special algorithms for caching ViewHolder in any time. So next onBindViewHolder(...) may not work, for ex. if view is static, or something else.
And about your question you think to use RecycleView for dynamic changed Views. DON'T DO IT! Because RecycleView invalidates views and has caching system, so you will have a lot of problems.
Use LinkedListView for this task!

Click on last item in AdapterView in Espresso

I'm working on a note taking app. I add a note, and it get's added to the bottom of the list. As the last assertion in the espresso test, I want to make sure that the ListView displays a listItem that has just been added. This would mean grabbing the last item in the listView. I guess you might be able to do it in other ways? (e.g. get the size of adapted data, and go to THAT position? maybe?), but the last position of the list seems easy, but I haven't been able to do it. Any ideas?
I've tried this solution, but Espresso seems to hang. http://www.gilvegliach.it/?id=1

1. Find the number of elements in listView's adapter and save it in some variable. We assume the adapter has been fully loaded till now.:
final int[] numberOfAdapterItems = new int[1];
onView(withId(R.id.some_list_view)).check(matches(new TypeSafeMatcher<View>() {
#Override
public boolean matchesSafely(View view) {
ListView listView = (ListView) view;
//here we assume the adapter has been fully loaded already
numberOfAdapterItems[0] = listView.getAdapter().getCount();
return true;
}
#Override
public void describeTo(Description description) {
}
}));
2. Then, knowing the total number of elements in listView's adapter you can scroll to the last element:
onData(anything()).inAdapterView(withId(R.id.some_list_view)).getPosition(numberOfAdapterItems[0] - 1).perform(scrollTo())

Can't get RecyclerView.Adapter to Properly Display

I followed this example here: https://developer.android.com/training/material/lists-cards.html
What's Happening:
The list (RecyclerView) is mixing up the data when I scroll. I.e. when I scroll back up after scrolling down, some of the list items are repeated, not displaying proper content.
Here is my onBindViewHolder method:
// cardsData is a List of MyCardItem (MyCardItem is just a holder of information,
// such as an id, String title, String summary, and other info to display on a card
#Override
public void onBindViewHolder(ViewHolder viewHolder, int position)
{
// Update view here
if (!cardsData.isEmpty())
{
viewHolder.updateDisplay(cardsData.get(position), activity, position);
}
}
Here is my updateDisplay method found inside the ViewHolder class:
// Set ID
if (item.getID() != null)
{
mIDView.setText(item.getID());
}
// Set Title
if (item.getTitle() != null)
{
mTitleView.setText(item.getTitle());
}
// Set Summary
if (item.getSummary() != null)
{
mSummaryView.setText(Html.fromHtml(item.getSummary()));
}
// Image
if (item.hasImage())
{
// Display image here
}
I believe it has something to do with the fact that sometimes the data is null, so I choose not to display it. Not all items (cards) will have an image to display, so this is why I check for if the item is supposed to have an image. If it does, then I do some fancy code to show an image (and making the other views GONE so I can only show that image, etc.).
While debugging, I forced all cards to display their id and position in the title. I can confirm that all ids and positions are in their proper places. When I force (removing the if check for id, title, and summary) the id, title, and summary to display, even if null, that content becomes unaffected. However, this does not solve my image situation (won't always have an image). I'll then have some images taking up the place for a certain id/position, where it should not (i.e. instead of displaying the summary text, it shows an image that isn't supposed to be there).
Any input as to why this is happening in my RecyclerView?

RecyclerView, just the same as ListView and GridView, reuses views whenever possible. That means while you scroll, views that fall off the top are used for the views on the bottom, etc. This greatly improves the memory efficiency and scroll performance. This means if you don't reset all of the state on a new item, you'll see state left over from the last time this view was used.
Instead, you should always reset all the of the state:
if (item.getID() != null) {
mIDView.setText(item.getID());
} else {
mIDView.setText("");
}
// etc...
Also, there shouldn't be any situations where you need to check for cardsData.isEmpty() - instead, whenever you update cardsData, you should be calling the appropriate notifyXXX method (such as notifyItemInserted() or in the worse case notifyDataSetChanged()) which will automatically refresh the list appropriately.

Implement
public long getItemId(int position) {}
otherwise, you'll see repeated items in RecyclerView.

Add these two and you are good to go !
#Override
public long getItemId(int position) {
return position;
}
#Override
public int getItemViewType(int position) {
return position;
}

Also in addition to previous answer you can check view on emptiness, for example:
if (TextUtils.isEmpty(viewHolder.item.getText())) {
viewHolder.item.setText(object.getItem());
}

To elaborate on ViliusK's answer. This implementation will work:
#Override
public long getItemId(int position) {
Object obj = getItemAtPosition(position);
return obj.hashCode();
}