Develop Reference

hide only a view from all recycler view items

I have a recycler view item that has few Views. I have a setting that will set the visibility of one Image view after the Recycler view is displayed. What is the best way to achieve this behavior?
What I tried, in the adapter ViewHolder class, I set a boolean that would hide the element and then call notifysetDataChanged()
public static class ViewHolder extends RecyclerView.ViewHolder {
public ImageView imageView;
public ViewHolder(View itemView) {
super(itemView);
.....
}
public void bind(item: Model){
//check and set visibility
if(showImage) imageview.setVisibility
else imageview.setVisibility
}
}
Calling this bind function from onBindViewHolder.
Is there any better way to achieve this as all the data remain the same only one visibility is changed?

your bind method is fine, but calling notifyDataSetChanged() will make your whole list redraw, all items. it's way better for perfomance to redraw only these items which has changed, use then notifyItemChanged(int position). calling it will make only single onBindViewHolder call with desired position, thus only one desired item will be redrawn (your bind call)
note there are more methods for preventing whole list redraw:
notifyItemChanged(int)
notifyItemInserted(int)
notifyItemRemoved(int)
notifyItemRangeChanged(int, int)
notifyItemRangeInserted(int, int)
notifyItemRangeRemoved(int, int)

Are you try this?
android:visibility="gone"

Radio button are not working normally in my Recycler View. Multiple Radio Buttons got selected of the view which are not visible with the focused one

I'm using a Recycler View to show all the images from the galley or the external storage of a device in a Grid Layout Manager. And I'm using a Radio Button to show if the image is selected or not.
PROBLEM
Whenever I select or deselect a Radio Button from the visible Views in the Recycler View some other Views which are outside the Visible Screen got selected or deselected.
It is like I'm pressing on the same View of the Recycler View, but the images are different.
PROBLEM

well that's because of the recycler view concept of reusing the views instead of creating new views every time you scroll.
you see if you have 100 items you want to show in a recycler view and only 20 of them could appear to the user, recycler view creates only 20 view holder to represent the 20 items, whenever the user scroll recycler view will still have 20 view holder only but will just switch the data stored in this view holders rather than create new view holders.
now to handle selection of your items there's two ways to do this.
the naive way
hold selection in a boolean array inside the recycle view adapter.
whenever the user scrolls, the adapter calls onBindViewHolder to update the visible viewholder with the proper data.
so when onBindViewHolder gets called just set the radio button selection according the boolean array using the position sent in the method call
at the end of your usage to the recycler view you can create a getter method in the adapter to get the selection array list of boolean and pass the data based on it
public class PhotosGalleryAdapter extends RecyclerView.Adapter<PhotosGalleryViewHolder> {
ArrayList<Your_Data_ClassType> data;
ArrayList<Boolean> dataSelected ;
public PhotosGalleryAdapter(ArrayList<Your_Data_ClassType> data) {
this.data = data;
dataSelected = new ArrayList<>(data.size()) ;
}
...
#Override
public void onBindViewHolder(#NonNull PhotosGalleryViewHolder holder, int position) {
...
RadioButton radioButton = holder.getRadioButton()
radioButton.setChecked(dataSelected.get(position));
radioButton.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
#Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
dataSelected.set(holder.getAbsoluteAdapterPosition() , isChecked) ;
}
});
...
}
}
the other way is to use a selection tracker and it should be the correct way to handle selections in a recycler view.
the problem with this way is it needs a lot of editing to the code and creating new classes to include as parameters in the selection tracker, but in the end you'll find it worth the time you spent on it.
in order to start with this way you need to do the following :
firstly, decide what should be a key (String-Long-Parcelable) so the tracker should use to differentiate between your data , the safest way is either String or Parcelable as I once tried Long and ended up with lots and lots of problems (in your case I will assume it's the photo's uri which will be of type string)
secondly, you need to create two new classes, one that extends ItemDetailsLookup, and the other extends ItemKeyProvider, and should use the key as their generic type (the type that is put between <> )
your two classes should look like this (that you might copy them straight forward)
the one that extends ItemKeyProvider :
public class GalleryItemKeyProvider extends ItemKeyProvider<String>{
PhotosGalleryAdapter adapter ;
/**
* Creates a new provider with the given scope.
*
* #param scope Scope can't be changed at runtime.
*/
public GalleryItemKeyProvider(int scope,PhotosGalleryAdapter m_adapter) {
super(scope);
this.adapter = m_adapter;
}
#Nullable
#Override
public String getKey(int position) {
return adapter.getKey(position);
}
#Override
public int getPosition(#NonNull String key) {
return adapter.getPosition(key);
}
}
the one that extends ItemDetailsLookup :
public class GalleryDetailsLookup extends ItemDetailsLookup<String> {
private final RecyclerView recView ;
public GalleryDetailsLookup(RecyclerView m_recView){
this.recView = m_recView;
}
#Nullable
#Override
public ItemDetails<String> getItemDetails(#NonNull MotionEvent e) {
View view = recView.findChildViewUnder(e.getX(), e.getY());
if (view != null) {
RecyclerView.ViewHolder holder = recView.getChildViewHolder(view);
if (holder instanceof PhotosGalleryViewHolder) {
return ((PhotosGalleryViewHolder) holder).getItemDetails();
}
}
return null;
}
}
thirdly, you should include this new two methods in your adapter to be used by the above classes
public class PhotosGalleryAdapter extends RecyclerView.Adapter<PhotosGalleryViewHolder> {
...
public String getKey(int position) {
return data.get(position).getUri();
}
public int getPosition(String key) {
for (int i = 0; i < data.size(); i++) {
if (data.get(i).getUri() == key) return i;
}
return 0;
}
...
}
forthly (if there's an english word called forthly), you should initialize the tracker with all the above classes that were created before and he will handle the rest, the tracker takes as parameters
a unique selection tracker id (if that will be the only selection tracker you will use then name it anything)
the ItemKeyProvider that we created
the DetailsLookup that we created
a String-Long-Parcelable Storage to store the keys that were selected in (in our case it will be a String Storage)
a Selection predicate, it's responsible to handle the way of selection you want to do, you want it to be able to (select only one item-multiple selection with no limits- based on a weird algorithm like even only or odd only), in my case I will use a default multiple selection one but if you want to alter it with another selection algorithm you should create a new class that extends SelectionPredicates and implement your way of selection, you could also just check the other default ones might be what you're looking for.
anyway, that's how the initialization should look (you should put this code wherever you initialize your recycler view at whether it's in fragment or activity method):
private void initRecycleView() {
...
SelectionTracker<String> tracker = new SelectionTracker.Builder<>("PhotosGallerySelection",
Your_Recycler_View,
new GalleryItemKeyProvider(ItemKeyProvider.SCOPE_MAPPED, photosAdapter),
new GalleryDetailsLookup(Your_Recycler_View),
StorageStrategy.createStringStorage())
.withSelectionPredicate(SelectionPredicates.createSelectAnything())
.build();
...
}
I didn't find a way to let me initialize the adapter with data and then create the tracker inorder to make the viewholders know about their selection or not, so in this case I firstly created the tracker and then made the adapter know about it's data using a setter and notifyDataSetChanged
what I mean by that is after creating the tracker instantly set the tracker and data to the adapter, so the initRecycleView should look like this
private void initRecycleView() {
...
SelectionTracker<String> tracker = new SelectionTracker.Builder<>("PhotosGallerySelection",
Your_Recycler_View,
new GalleryItemKeyProvider(ItemKeyProvider.SCOPE_MAPPED, photosAdapter),
new GalleryDetailsLookup(Your_Recycler_View),
StorageStrategy.createStringStorage())
.withSelectionPredicate(SelectionPredicates.createSelectAnything())
.build();
photosAdapter.setTracker(tracker);
photosAdapter.setData(data);
photosAdapter.notifyDataSetChanged();
...
}
Last but no least, you should handle how the view holders should know if they were selected or not, so you should let the adapter know about the tracker and its data by creating a setter method in it, that's how the adapter should look like in the end :
public class PhotosGalleryAdapter extends RecyclerView.Adapter<PhotosGalleryViewHolder> {
ArrayList<Your_Data_Class> data;
private SelectionTracker<String> tracker;
public PhotosGalleryAdapter() {
data = new ArrayList<>();
}
public ArrayList<Your_Data_Class> getData() {
return data;
}
public void setData(ArrayList<Your_Data_Class> m_data) {
this.data = m_data;
}
#Override
public ScheduleViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
...
}
#Override
public void onBindViewHolder(#NonNull PhotosGalleryViewHolder holder, int position) {
...
boolean isSelected = tracker.isSelected(data.get(i).getUri());
RadioButton radioButton = holder.getRadioButton;
radioButton.setChecked(isSelected);
}
#Override
public int getItemCount() {
return data.size();
}
public String getKey(int position) {
return data.get(position).getUri();
}
public int getPosition(String key) {
for (int i = 0; i < data.size(); i++) {
if (data.get(i).getUri() == key) return i;
}
return 0;
}
public void setTracker(SelectionTracker<String> m_tracker) {
this.tracker = m_tracker;
}
}
(as you may notice if you initialized the adapter with its data through the constructor, when he asks the tracker if there were an item selected or not, it will result in a NullPointerException as at the moment of initializing the adapter you still didn't initialize the tracker)
that way you could keep track of your selection the way google suggests in their documentation (which I honestly don't know why the made it very complicate like that).
if you want to know all the selected item in the end of your application/fragment use, you should call tracker.getSelection() which will return a Selection List for you to iterate on
There's a tiny problem/feature with the tracker that it won't start selecting the first item until you use a long press on it, that happens only in the first item you select, if you do want this feature (start selecting mode by long press) then leave it as it is
incase you don't want it you can make the tracker select a ghost key (any unique string key that means nothing to your data) at the beginning which should later enable the selection mode with a simple click on any photo
tracker.select("");
this also the way to make a default/old selection at the beginning, you could make a for loop and call tracker.select(Key) if you do want the tracker to start with few items being selected
N.B : incase you use the Ghost Key method you should watchout that the selection array that will get returned when you call tracker.getSelection() will also contain this Ghost Key.
at the end if you do have the curiosity of reading about selection tracker in the documentation follow this link
or maybe if you know how to read kotlin follow this two links
implementing-selection-in-recyclerview
a guide to recyclerview selection
I was stuck in the selection problem for days before I figure how to do all that so I hope you find your way through it.

Omar Shawky has covered the solutions.
With my answer I will stress on the reason why someone may face this sort of an issues with recycler views and how to avoid this common issue in the future (avoiding pitfalls).
Reason:
This issue happens because RecyclerView recycles views. So a RecyclerView item's view once inflated can get reused to show another off screen (to be scrolled to) item. This helps reduces re-inflation of views which otherwise can be taxing.
So if the radio button of an item's view is selected, and the same view gets reused to show some other item, then that new item can also have a selected radio button.
Solution:
The simplest solution for such issues is to have an if else logic in your ViewHolder to provide logic for both selected and de-selected cases. We also do not rely on information from radio button itself for initial setup (we do not use radioButton.isSelected() at the time of setup)
e.g code to write inside your ViewHolder class:
private boolean isRadioButtonChecked = false; // ViewHolder class level variable. Default value is unchecked
// Now while binding in your ViewHolder class:
// Setup Radio button (assuming there is just one radio button for a recyclerView item).
// Handle both selected and de-selected cases like below (code can be simplified but elaborating for understanding):
if (isRadioButtonChecked) {
radioButton.setChecked(true);
} else {
radioButton.setChecked(false);
}
radioButton.setOnCheckedChangeListener(
(radioButton, isChecked) -> isRadioButtonChecked = isChecked);
Do not do any of the following while setting up:
private boolean isRadioButtonChecked = false; // class variable
//while binding do not only handle select case. We should handle both cases.
if (isRadioButtonChecked) { // --> Pitfall
radioButton.setChecked(true);
}
radioButton.setOnCheckedChangeListener((radioButton, isChecked) -> isRadioButtonChecked = isChecked);
OR
// During initial setup do not use radio button itself to get information.
if (radioButton.isChecked()) { // --> Pitfall
radioButton.setChecked();
}

When press back button listview going top. How to fix that?

In my codes there is two fragment. List page and detail page. There is lot of alphabetic item on list page. And when i clicked some item opening the detail page. But when i press back button, the list doesn't stay same position. It goes to the top. I searched some solution but i think that's not common issue. I couldn't find different answers. Is there anyone to help me?

At first glance, it looks like it's one of your calls to: dictionaryFragment.resetDatasource(source);
Which is resetting the Adapter on your ListView to a brand new ArrayAdapter. This will reset the ListView to the top because the adapter is an entirely new object. The ListView no longer has any idea about the old ArrayAdapter and thus resets to the top.
public void resetDatasource (ArrayList<String> source){
mSource=source;
adapter = new ArrayAdapter<String>(getContext(),R.layout.kelimelistesi, mSource);
dicList.setAdapter(adapter);
}
Rather than calling
adapter = new ArrayAdapter<String>(getContext(),R.layout.kelimelistesi, mSource);
dicList.setAdapter(adapter);
You should do more like this:
public class DictionaryFragment ... {
private Adapter mAdapter;
public View onCreateView(...) {
// Init the layout here
// Put some other ArrayList here if you have one initially, else an empty one to start
mAdapter = new ArrayAdapter<String>(getContext(), R.layout.kelimelistesi, new ArrayList<String>());
dicList.setAdapter(mAdapter);
}
public void resetDatasource(ArrayList<String> source) {
mAdapter.clear();
mAdapter.addAll(source);
mAdapter.notifyDataSetChanged();
}
...
}
This difference now is that the same mAdapter instance is bound to dicList the whole time, but only the underlying data to display changed. Think of a ListView/RecyclerView's Adapter as a class that takes some input data and binds it to some UI elements. In this case, each String in the ArrayAdapter is displayed in some UI element like a TextView or what not.
ALSO important: note that we call notifyDataSetChanged() AFTER we have cleared the old data and added all the new data. This will help avoid flickering and scrolling issues from trying to elements one at a time.

Adding an onClick to a part of a RecyclerView item

I've been working on an online shop type of application, and I've hit a bump: I've been tasked to add a favorites system, but I can't figure out how to enable pressing a button that's part of the RecyclerView item to add it to favorites.
(In this case, the heart, which is supposed to turn to a full heart when clicked)

Add a boolean value for favourite in your list . Initially , keep it false .
You need to have two drawables , one for selected state and another for unselected state .
In your onBindViewHolder , set the drawable on runtime on the basis of above condition .
if(list.isfav)
{
holder.ivHeart.setImageDrawable(ContextCompat.getDrawable(context,(R.drawable.selected));
}else{
holder.ivHeart.setImageDrawable(ContextCompat.getDrawable(context,(R.drawable.unselected));
}
Put onClick on this ivHeart eg:
holder.ivHeart.setOnClickListener(v -> {
if(list.isfav) {
list[adapterPosition].isfav = false;
}else{
list[adapterPosition].isfav = true;
}
notifyItemChanged(adapterPosition);
});
Dont forget to notify the item while changing item .

In your RecyclerView adapter's onBindViewHolder() method, add click listener to your view and change the drawable programmatically.
The code will be something like this
#Override
public void onBindViewHolder(ViewHolder holder, int position) {
super.onBindViewHolder(holder, position);
holder.your_like_imageview.setOnClickListener{
holder.your_like_imageview.setImageDrawable(ContextCompat.getDrawable(context,R.drawable.something_else));
};
}

I'm assuming you're using an ImageView for the heart. What you can do is set a click listener on that ImageView and process that click.
An ideal way to do this would be to use an interface to handle click events that you pass to the Adapter.
However you could do something like this in the onBindViewHolder method:
imageView.setOnClickListener {
// depending your logic change the tint for the icon or the drawable
onClick(data[position], addToWishlist)
notifyDataSetChanged()
}
The onClick method will receive the particular item and a flag to add or remove it from
the wishlist:
fun onClick(data: Data, addToWishlist: Boolean) {
// you can perform the addition/ deletion from the wishlist here
}

Programmatic changes to a view aren't applied

I made a list that's loaded with Contact friends and the user can select them by tapping on them. If a person is selected, the listitem's backgorund changes colour, if deselected, the bg colouring goes away.
Problem is, when I call my method on an OnClickListener, it's fine.
When I however call it in a loop to colour already selected friends (e.g. when revisiting the list), it doesn't do the colouring.
The loop that goes through the elements to call colorize if needed:
for (int i = 0; i < adapter.getCount();i++){
ContactFriend cf = (ContactFriend) adapter.getItem(i);
View v = getViewByPosition(i,listView);
colorizeFriendBg(v, cf);
adapter.notifyDataSetChanged();
}
note I do the exact same in the listener and it works fine there.
And the colorizer:
private void colorizeFriendBg(View v, ContactFriend friend){
if(friend.isSelected()){
v.setBackgroundColor(0x993399ff);
}else{
v.setBackgroundColor(0x00000000);
}
v.invalidate();
}
This issue is quite strange and I have no idea what to do in order to make it right. The whole bunch is called from onActivityCreated, if that matters.
Edit:
I debugged it of course and the code runs and should change the colour, not running isn't the issue.
Edit again:
here's the listener implementation:
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
ContactFriend fr = (ContactFriend) adapter.getItem(position);
addToSelected(fr);
//TODO: make it switch some BG colour when clicked. use getViewByPosition.
View v = getViewByPosition(position,listView);
colorizeFriendBg(v,fr);
adapter.notifyDataSetChanged();
}
});

what type of item View are you getting from the Adapter?
that View could / should implement colorize() and color itself;
for example: v.colorize(contact.isSelected()) to switch colors.
or with Android Data-Binding XML (where the viewModel is an instance of Contact):
<data class="com.acme.databinding.ContactViewHolderBinding">
<variable name="viewModel" type="com.acme.model.Contact"/>
</data>
...
android:backgroundColor="#{viewModel.isSelected ? R.color.MAGENTA : R.color.BLACK}"
class Contact just would require a getter and a setter for property isSelected.
one actually can also bind event handlers, which would be an alternate approach.

You need to call invalidate() on your view to make the color changes visible.
invalidate() forces a redraw with the new colors.