Develop Reference

Why is my recyclerView not displaying any data?

I have implemented a RecyclerView and customer Adapter many times, but for some reason I cannot get this one to display any data. I am feeding in data from JSON using retrofit and calling notifyDataSetChanged() once this has been loaded, yet it still remains blank. I have stripped this back to just one text view to try and simplify but still not getting anything. Can anyone see where I am going wrong here?
When I debug, I am getting the List to contain data so I am definitely parsing the data correctly, I just cant get it display in the recycler view. I have even checked the list.size() in the loadTrailerList method and it has data.
My Activity onCreate method:
trailerAdapter = new TrailerAdapter(this);
trailerRecyclerView = findViewById(R.id.trailer_recycler_view);
trailerRecyclerView.setLayoutManager(new LinearLayoutManager(this));
trailerRecyclerView.setAdapter(trailerAdapter);
Retrofit onResponse method:
if (response.body() != null) {
trailers = response.body().getTrailers();
}
trailerAdapter.loadTrailerList(response.body().getTrailers());
My custom adapter:
public class TrailerAdapter extends RecyclerView.Adapter<TrailerAdapter.TrailerViewHolder> {
private final List<Trailer> trailerList = new ArrayList<>();
private final TrailerClickListener listener;
public TrailerAdapter(TrailerClickListener listener) {
this.listener = listener;
}
#NonNull
#Override
public TrailerViewHolder onCreateViewHolder(#NonNull ViewGroup viewGroup, int i) {
View itemView = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.trailer_list_item, viewGroup, false);
return new TrailerViewHolder(itemView, this);
}
#Override
public void onBindViewHolder(#NonNull TrailerViewHolder trailerViewHolder, int i) {
trailerViewHolder.trailerTitle.setText(trailerList.get(i).getName());
}
#Override
public int getItemCount() {
return trailerList.size();
}
public void loadTrailerList(List<Trailer> trailers) {
this.trailerList.clear();
if (trailers != null) {
trailers.addAll(trailers);
}
notifyDataSetChanged();
}
class TrailerViewHolder extends RecyclerView.ViewHolder {
final TrailerAdapter trailerAdapter;
private final TextView trailerTitle;
private TrailerViewHolder(#NonNull View itemView, TrailerAdapter trailerAdapter) {
super(itemView);
this.trailerAdapter = trailerAdapter;
trailerTitle = itemView.findViewById(R.id.text_view_trailer_title);
itemView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
listener.onTrailerClicked(trailerList.get(getAdapterPosition()));
}
});
}
}
}
My List Item XML
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<TextView
android:id="#+id/text_view_trailer_title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Play Trailer" />
</LinearLayout>
the recycler view in my activity XML:
<android.support.v7.widget.RecyclerView
android:id="#+id/trailer_recycler_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#color/colorPrimary"
app:layout_constraintTop_toBottomOf="#+id/trailer_divider">
</android.support.v7.widget.RecyclerView>
I am grateful for anyone that can point me in the right direction

It is because you are sending a list to adapter but, you are not initializing your list which is used in the adapter.
try this.
public void loadTrailerList(List<Trailer> trailers) {
this.trailerList.clear();
if (trailers != null) {
trailerList = trailers;
}
notifyDataSetChanged();
}

Doh! I just realised what I was doing wrong:
In my loadTrailerList() method in my adapter, I was calling:
trailers.addAll(trailers);
instead of:
trailerList.addAll(trailers);
to load the list of items into the actual ArrayList! whoops!

Updating contents of a RecyclerView when item of another RecyclerView is clicked

So I am trying to create an android app on alcohol and mixers, but have been stuck on the following problem for a while now...
I want to display every alcohol category (eg: Gin, Vodka, Whiskey, etc..) in a RecyclerView that scrolls horizontally, and every alcohol type (eg: Bourbon and Scotch for the Whiskey Category) in a RecyclerView that scrolls vertically.
I have created one adapter for each RecyclerView (CategoryAdapter for the horizontal RecyclerView called category, and MixerAdapter for the vertical RecyclerView called categoryDetails).
So far I've managed to create and display category as desired, but have some difficulties for categoryDetails.
Basically, I can't figure out how to update the contents of categoryDetails when an item of category is selected:
For example
If the user selects Whiskey in category, I want categoryDetails to display Bourbon and Scotch.
If the user then selects Gin, I want categoryDetails to only display Gin and Flavoured Gin, etc...
I hope I've been clear enough on what it is I want to accomplish!
Any help would be much appreciated, thanks!!
Here is a screenshot of how the screen appears when the activity is loaded.
If a user selects Rum (white on black RecyclerView), I want the RecyclerView currently showing Gin and Flavored Gin (black on white RecyclerView) to show the alcohols associated with the Rum category.
Screenshot
Here is the XML file holding the two recyclerViews category and categoryDetails
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".TipsDrinks">
<android.support.v7.widget.RecyclerView
android:id="#+id/category"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginTop="16dp"
android:background="#android:color/black"
android:orientation="horizontal"
android:scrollbars="horizontal"
android:visibility="visible"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/SpinnerPrompt" >
</android.support.v7.widget.RecyclerView>
<android.support.v7.widget.RecyclerView
android:id="#+id/categoryDetails"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginBottom="8dp"
android:background="#android:color/white"
android:orientation="horizontal"
android:scrollbars="vertical"
android:visibility="visible"
app:layout_constraintBottom_toTopOf="#+id/adView4"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/category"
app:layout_constraintVertical_bias="0.0">
</android.support.v7.widget.RecyclerView>
</android.support.constraint.ConstraintLayout>
The Class associated with the previous layout
public class TipsDrinks extends AppCompatActivity {
private CategoryAdapter categoryAdapter; // Adapter used for the category RecyclerView
public MixerAdapter mixerAdapter; //Adapter used for the categoryDetails RecyclerView
private RecyclerView categories; // The RecyclerView holding the name of each alcohol category
public RecyclerView catDetails; // The RecyclerView holding each type of that alcohol category
private DrinkMenu drinkMenu; // The DrinkMenu is another Class holding every Alcohol Category, the type of each alcohol and the mixers good with it
private ArrayList<String> drinkCat = new ArrayList<>(); // A String ArrayList holding the name of each alcohol category (Gin, Vodka, Rum, Whiskey, Other)
private ArrayList<Drink> drinkMixers = new ArrayList<>(); // A Drink(String, ArrayList<String>) ArrayList holding the mixers of every Drink
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_tips_drinks);
categories = findViewById(R.id.category);
catDetails = findViewById(R.id.categoryDetails);
drinkMenu = new DrinkMenu();
setCategoryView(); // Creates the category RecyclerView
setDrinkMixers(); // Creates the categoryDetails RecyclerView
}
private void setCategoryView(){
categoryAdapter = new CategoryAdapter(drinkCat);
RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(TipsDrinks.this, LinearLayoutManager.HORIZONTAL, false);
categories.addItemDecoration(new DividerItemDecoration(TipsDrinks.this, DividerItemDecoration.HORIZONTAL));
categories.setLayoutManager(layoutManager);
categories.setItemAnimator(new DefaultItemAnimator());
categories.setAdapter(categoryAdapter);
prepareCategories();
}
private void prepareCategories(){
drinkCat.clear();
drinkCat.addAll(drinkMenu.getDrinkCategories());
for (String drink : drinkCat) {
System.out.println(drink);
}
categoryAdapter.notifyItemInserted(drinkCat.size() - 1);
}
private void setDrinkMixers() {
mixerAdapter = new MixerAdapter(drinkMixers);
RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getApplicationContext());
catDetails.addItemDecoration(new DividerItemDecoration(this, DividerItemDecoration.VERTICAL));
catDetails.setLayoutManager(layoutManager);
catDetails.setItemAnimator(new DefaultItemAnimator());
catDetails.setAdapter(mixerAdapter);
prepareMixers();
}
private void prepareMixers() {
drinkMixers.clear();
drinkMixers.addAll(drinkMenu.getDrinkMixers(categoryAdapter.getCurrentCategory()));
mixerAdapter.notifyItemChanged(drinkMixers.size() -1);
}
}
The CategoryAdapter Class for the category RecyclerView
public class CategoryAdapter extends RecyclerView.Adapter<CategoryAdapter.MyViewHolder> {
private List<String> drinkList; //A List of String holding the category for each drink
private String textName = "Gin";
class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener{
private TextView name; // The TextView holding the name of the category
MyViewHolder(View view) {
super(view);
view.setOnClickListener(this);
name = view.findViewById(R.id.catName);
}
#Override
public void onClick(View v) {
//Code to update the contents of the categoryDetails RecyclerView
}
}
CategoryAdapter(ArrayList<String> drinkList) { this.drinkList = drinkList; }
#Override
public CategoryAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View itemView = LayoutInflater.from(parent.getContext())
.inflate(R.layout.category_text, parent, false);
return new MyViewHolder(itemView);
}
#SuppressLint("SetTextI18n")
#Override
public void onBindViewHolder(CategoryAdapter.MyViewHolder holder, int position) {
String drink = drinkList.get(position);
holder.name.setText(drink);
textName = holder.name.getText().toString();
}
#Override
public int getItemCount() {
return drinkList.size();
}
public String getCurrentCategory() {
return textName;
}
}
The MixerAdapter Class for the categoryDetails RecyclerView
public class MixerAdapter extends RecyclerView.Adapter<MixerAdapter.MyViewHolder>{
private List<Drink> mixerList;
class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener{
TextView mixerCat, mixers;
MyViewHolder(View view) {
super(view);
view.setOnClickListener(this);
mixerCat = view.findViewById(R.id.mixerCat2);
mixers = view.findViewById(R.id.mixers2);
}
#Override
public void onClick(View v) {
if (mixers.getVisibility() == mixerCat.getVisibility()) {
mixers.setVisibility(View.GONE);
}
else {
mixers.setVisibility(View.VISIBLE);
}
}
}
MixerAdapter(ArrayList<Drink> mixerList) {
this.mixerList = mixerList;
}
#Override
public MixerAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View itemView = LayoutInflater.from(parent.getContext())
.inflate(R.layout.drinks_row, parent, false);
return new MixerAdapter.MyViewHolder(itemView);
}
#SuppressLint("SetTextI18n")
#Override
public void onBindViewHolder(MixerAdapter.MyViewHolder holder, int position) {
Drink drink = mixerList.get(position);
StringBuilder mixerStringList = new StringBuilder("");
holder.mixerCat.setText(drink.getSorM());
for (String mixer: drink.getMixers()) {
mixerStringList.append(mixer).append("\n");
}
holder.mixers.setText(mixerStringList.toString().trim());
}
#Override
public int getItemCount() {
return mixerList.size();
}
}

Create a callback interface in CategoryAdapter. When user clicks on an item in Category RecycleView, it's activity responsibility to populate MixerAdapter with new items as per selection.
CategoryAdapter
public class CategoryAdapter extends RecyclerView.Adapter<CategoryAdapter.MyViewHolder> {
private CategoryInterface callback;
CategoryAdapter(ArrayList<String> drinkList, CategoryInterface listener) {
this.drinkList = drinkList;
callback = listener;
}
#Override
public void onClick(View v) {
//Code to update the contents of the categoryDetails RecyclerView
callback.onItemSelected(getAdapterPosition());
}
public interface CategoryInterface {
void onItemSelected(int position);
}
}
Activity
public class TipsDrinks extends AppCompatActivity implements CategoryInterface {
private void setCategoryView(){
categoryAdapter = new CategoryAdapter(drinkCat, this);
}
#Override
void onItemSelected(int position) {
//Reassign items in MixerAdapter
}
}

that depends on your implementations , one global method which should work for all implementations is using HolderView method and using onTouchListener on the groups's root view
v.setOnTouchListener(new View.OnTouchListener() {
#Override
public boolean onTouch(View v, MotionEvent event) {
if(event.getAction() == MotionEvent.ACTION_UP){
//the child should expand and be updated
}
return false;
}
});

How to add child item to last item from RecyclerView?

Actually i'm trying to make an app that take restaurant orders and i'm having some issues after adding child item to my order.
I have a recyclerView where i have different type's of food when i press on one of them i add it to recyclerView that work's something like a notebook, then i have an button that open an AlertDialog in which there is another recyclerView with variant's.
Example: i press on PIZZA from food recyclerView it's add it to the notebook after i press on variant's and i can add "WITH PEPERONI" or "LARGE" or both.
I have followed this guide ( here github project from the guide) for making the recyclerView with child item.
Now the issue is how can i add the child item to the last parent item?
like i'm adding parent item using this:
dummyParentDataItem = new ItemPTERM();
dummyParentDataItem.setButton_name(filteredList.get(position).getDeskS());
dummyParentDataItem.setQuant( Integer.parseInt(filteredList.get(position).getQuant()));
dummyChildDataItems = new ArrayList<>();
dummyParentDataItem.setChildDataItems(dummyChildDataItems);
itemCassas.add(dummyParentDataItem);
And this when i add a child from variant's recyclerView
dummyChildDataItem = new DummyChildDataItem();
dummyChildDataItem.setChildName(tipo.toString());
dummyChildDataItems.add(dummyChildDataItem);
dummyParentDataItem.setChildDataItems(dummyChildDataItems);
itemCassas.add(dummyParentDataItem);
but obviously the app crash because that don't know which is the last paren't item to which add the child.
When i try to put both parent and child when i'm adding food from recyclerView with:
dummyParentDataItem = new ItemPTERM();
dummyParentDataItem.setButton_name(filteredList.get(position).getDeskS());
dummyParentDataItem.setQuant( Integer.parseInt(filteredList.get(position).getQuant()));
dummyChildDataItems = new ArrayList<>();
dummyChildDataItem = new DummyChildDataItem();
dummyChildDataItem.setChildName("WITH PEPERONI");
dummyChildDataItems.add(dummyChildDataItem);
dummyParentDataItem.setChildDataItems(dummyChildDataItems);
itemCassas.add(dummyParentDataItem);
that obviously works but i have to add the child in a separate method to the last parent.
How can i do it? any suggestion?
Here is also my adapter code:
public class AdapterPTERM extends RecyclerView.Adapter<AdapterPTERM.ExampleViewHolder> {
private ArrayList<ItemPTERM> mExampleList;
#NonNull
#Override
public ExampleViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.recyclerview_pterm,parent,false);
return new ExampleViewHolder(v);
}
AdapterPTERM(ArrayList<ItemPTERM> exampleList){
mExampleList = exampleList;
}
#Override
public void onBindViewHolder(#NonNull ExampleViewHolder holder, int position) {
ItemPTERM item = mExampleList.get(position);
holder.desc.setText(item.getBtnName());
holder.qta.setText(String.valueOf(item.getQuant()));
int noOfChildTextViews = holder.linearLayout_childItems.getChildCount();
int noOfChild = item.getChildDataItems().size();
if (noOfChild < noOfChildTextViews) {
for (int index = noOfChild; index < noOfChildTextViews; index++) {
TextView currentTextView = (TextView) holder.linearLayout_childItems.getChildAt(index);
currentTextView.setVisibility(View.GONE);
}
}
for (int textViewIndex = 0; textViewIndex < noOfChild; textViewIndex++) {
TextView currentTextView = (TextView) holder.linearLayout_childItems.getChildAt(textViewIndex);
currentTextView.setText(item.getChildDataItems().get(textViewIndex).getChildName());
}
if(position % 2 == 0 ){
holder.itemView.setBackgroundColor(Color.parseColor("#C0C0C0"));
}else if(position % 2 == 1){
holder.itemView.setBackgroundColor(Color.parseColor("#D3D3D3"));
}
}
#Override
public int getItemCount() {
return mExampleList.size();
}
public class ExampleViewHolder extends RecyclerView.ViewHolder {
public TextView desc;
public TextView qta;
private LinearLayout linearLayout_childItems;
private Context context;
ExampleViewHolder(View itemView) {
super(itemView);
desc = itemView.findViewById(R.id.Desc);
qta = itemView.findViewById(R.id.Qta);
linearLayout_childItems = itemView.findViewById(R.id.ll_child_items);
context = itemView.getContext();
int intMaxNoOfChild = 0;
for (int index = 0; index < mExampleList.size(); index++) {
int intMaxSizeTemp = mExampleList.get(index).getChildDataItems().size();
if (intMaxSizeTemp > intMaxNoOfChild) intMaxNoOfChild = intMaxSizeTemp;
}
for (int indexView = 0; indexView < intMaxNoOfChild; indexView++) {
TextView textView = new TextView(context);
textView.setId(indexView);
textView.setPadding(0, 20, 0, 20);
textView.setGravity(Gravity.CENTER);
textView.setBackground(ContextCompat.getDrawable(context, R.drawable.background_sub_module_text));
LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT);
linearLayout_childItems.addView(textView, layoutParams);
}
}
}
public void removeItem(int position) {
mExampleList.remove(position);
notifyItemRemoved(position);
}
}
Here is a screenshot of my activity

To display data in a RecylerView, you provide a list of items to its adapter.
To add a new element you just need to add the item to the list and call notifyDataSetChange() on the adapter.
For example you can create a new method in you adapter, like that:
public void addItem(ItemPTERM item){
mExampleList.add(item);
notifyDataSetChange();
}
EDIT
So what you can do is to allow your item to have a list of 'variants'.
For example if you select 'Pizza' and want to had 'big' and 'pepperoni', your item will be the pizza and 'big'and 'pepperoni' part of the variants list.
Food {
String name;
List<Variant> variants;
//... Other attributes
public void setVariant(Variant variant){
if (variants == null) // We want to initialise the array only when necessary
variants = new ArrayList<>();
variants.add(variant);
}
#Nullable
public List<Variant> getVariants(){
return variants;
}
}
Variant{
String name;
//... Other attributes
}
When you select a variant you add it to the appropriate Food object.
Approach 1
Then in your adapter, in the onBindViewHolder you can dynamically add the variants to the item;
This way is not the most optimised but should work:
Item layout
<!-- Food Views-->
...
<!-- Container for the variants -->
<LinearLayout
android:id="#+id/variants_list"
android:layout_width="match_parent"
android:orientation="vertical"
android:layout_height="wrap_content"/>
</LinearLayout>
Variant layout
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal">
<TextView
android:id="#+id/variant_name"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="#+id/variant_other_info"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
Adapter
final LayoutInflater mInflater;
List<Food> mFoods;
public FoodAdapter(Context context, ...){
//...
mInflater = LayoutInflater.from(context);
}
#Override
public void onBindViewHolder(#NonNull ExampleViewHolder holder, int position) {
Food food = mFood.get(position);
// Display food attributes
//...
// Clear the container to set fresh info
holder.variantsContainer.removeAllViews();
List<Variant> variants = food.getVariants();
if (variants != null && variants.size() > 0){
// Display the variants when necessary
for(Variant v : variants){
View vView = mInflater.inflate(R.layout.variant_layout);
TextView nameTV = vView.findViewById(R.id.variant_name);
nameTV.setText(v.getName());
// Set other fields values
// ...
holder.variantsContainer.addView(vView);
}
}
}
Approach 2
Another way to do it is to have a list of food object containing a list of variant as above, but to not use this list directly in the adapter.
Instead the adapter will use it's own list which will be both Food and Variant objects mix together. Your adapter should then be able to display 2 kinds of objects. This way is more flexible but you have to recreate the entire adapter list every time you change something.
For instance:
Let say you have 3 Food objects in the list. The first one has 1 variant, the second one none and the third one 2.
Then your adapter will get a list like that:
List<Object> items;
items will contain:
{food1, variant1a, food2, food3, variant3a, variant3b}
And then your adapter will have to use two different layout to display either the Food or the Variant object.
#NonNull
#Override
public ExampleViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
if (viewType == 0) { // if food
View vFood = mInflater.inflate(R.layout.food_layout, parent, false);
return new FoodViewHolder(vFood);
} else { // variant
View vVariant = mInflater.inflate(R.layout.variant_layout, parent, false);
return new VariantViewHolder(vVariant;
}
}
#Override
public int getItemViewType(int position) {
return (mItems.get(position) instanceof Food) ? 0 : 1;
}

How to show exactly ten rows in RecyclerView

I would like to always display exactly ten rows in a RecyclerView. RecyclerView does not have a configurable setting for this. One approach is to calculate the size of each row. I would like the table to take up half the screen and always show 0..10 items within that area. If more than 10 items the user would scrooll to see the items. Right now the default behavior of RecyclerView seems to be to keep pushing everything down as it grows.

#Override
public int getItemCount() {
if(list.size()>10){
return 10;
}else{
return list.size();
}
}
In your recycler view adapter class return get item count to 10 if size of array or list is greater than 10

Your guess is right it's working with a dynamic computation of row height, here is an example:
Simple class standing for data you want to display:
public class CustomItem {
private int counter;
public CustomItem(int counter) {
this.counter = counter;
}
public int getCounter() {
return counter;
}
public void setCounter(int counter) {
this.counter = counter;
}
}
And simple layout to display CustomItem in a list:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#android:color/darker_gray">
<TextView
android:id="#+id/txvTest"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="8dp"
android:text="Test"/>
</RelativeLayout>
RecyclerAdapter for this class, you will see that we set row height programmatically in onBindViewHolder method:
public class CustomItemRecyclerAdapter extends RecyclerView.Adapter<CustomItemRecyclerAdapter.SimpleItemViewHolder> {
private static int NB_OF_ITEM_TO_DISPLAY = 10;
private List<CustomItem> customItems;
private Context context;
private int rowHeight;
public class SimpleItemViewHolder extends RecyclerView.ViewHolder {
TextView txvTest;
RelativeLayout container;
public SimpleItemViewHolder(View itemView) {
super(itemView);
txvTest = (TextView) itemView.findViewById(R.id.txvTest);
container = (RelativeLayout) itemView;
}
}
public CustomItemRecyclerAdapter(Context context, List<CustomItem> customItems) {
this.context = context;
this.customItems = customItems;
}
public void setItemHeight(int parentHeightInPx){
// Height of a row is just parent height divided by number of row to display
this.rowHeight = parentHeightInPx / CustomItemRecyclerAdapter.NB_OF_ITEM_TO_DISPLAY;
// Notify adapter because items will need to be redraw to use newly set height
this.notifyDataSetChanged();
}
#Override
public SimpleItemViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View itemView = LayoutInflater.from(context).inflate(R.layout.custom_item, parent, false);
return new SimpleItemViewHolder(itemView);
}
#Override
public void onBindViewHolder(SimpleItemViewHolder holder, int position) {
CustomItem item = customItems.get(position);
holder.txvTest.setText("Item " + item.getCounter());
holder.txvTest.setBackgroundColor(item.getCounter());
// Row size magic is here!
RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.MATCH_PARENT, rowHeight);
holder.container.setLayoutParams(params);
}
#Override
public int getItemCount() {
return customItems.size();
}
}
Activity layout, with both a TextView used as placeholder for half the screen and the RecyclerView:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:background="#color/colorAccent"
android:text="TEST"/>
<android.support.v7.widget.RecyclerView
android:id="#+id/a_main_rcv_items"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#color/colorPrimary"
android:layout_weight="1"
android:scrollbars="vertical"/>
</LinearLayout>
And Activity code with comments to understand how it works ;):
public class MainActivity extends AppCompatActivity {
private RecyclerView recyclerView;
private CustomItemRecyclerAdapter adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Link to layout recycler view
recyclerView = (RecyclerView) findViewById(R.id.a_main_rcv_items);
// Create a simple linear layout manager and set it to recyclerview
RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);
// Create an instance of our custom Adapter
adapter = new CustomItemRecyclerAdapter(MainActivity.this, generateItems(20));
// Set this adapter
recyclerView.setAdapter(adapter);
// Listen for recycler view layout change event to get its height and then compute and set new rows height
recyclerView.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
#Override
public void onLayoutChange(View view, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
// Set item height using height of recyclerView
adapter.setItemHeight(view.getHeight());
// Need to simulate a scroll to force a redraw of recycler rows with new height... I have not find better for now...
recyclerView.scrollBy(0,1);
}
});
}
private List<CustomItem> generateItems(int nb) {
ArrayList<CustomItem> items = new ArrayList<>(nb);
for (int i = 1; i < nb + 1; i++) {
items.add(new CustomItem(i));
}
return items;
}
}

Android RecyclerView DefaultItemAnimator - Items moving weirdly

I have a problem with a simple multicolumn layout RecyclerView which is best reproducible on tablets. I have created a basic example with fully functional source code below, maybe it is easier to quickly run it, instead of trying to understand what I mean ;)
The main problem on tablets (where I have a grid layout) is, that items get strangely rearranged when hiding specific items and displaying them again (via notifyItemRemoved() and notifyItemInserted()). I think this can be even reproduced with removing and inserting only the first item. The layout manager inserts an extra row at the top and moves items from the first line below to fill it. (The example below removes and inserts every third item, starting with the first one)
I have different types of items (in the example red, green and blue items) and I want to toggle a specific type of items (in the example you can toggle the red items with a click on the FloatingActionButton).
The weird behavior that I want to fix can be reproduced by just clicking the FAB twice without scrolling before. This would first filter the red items and then display them again. When toggling the filter the second time you will notice that there is a row of items inserted above and items from the first row are moved to fill it.
If you didn't notice during the animation, just scroll up after toggling the filter.
I would expect that the first row stays where it is and that just the red items get displayed again.
Does anybody know how to fix that?
Here is the activity code:
public class MainActivity extends AppCompatActivity {
private RecyclerView recyclerView;
private TestAdapter adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
((FloatingActionButton) findViewById(R.id.fab)).setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(final View v) {
toggleFiltered();
}
});
final int columnCount = getColumnCount(300);
GridLayoutManager layoutManager = new GridLayoutManager(this, columnCount);
recyclerView.setLayoutManager(layoutManager);
adapter = new TestAdapter();
recyclerView.setAdapter(adapter);
recyclerView.setItemAnimator(new DefaultItemAnimator());
}
private void toggleFiltered() {
final boolean filtered = adapter.isFiltered();
adapter.setFiltered(!filtered);
if(filtered) {
adapter.notifyItemInserted(0);
adapter.notifyItemInserted(3);
adapter.notifyItemInserted(6);
adapter.notifyItemInserted(9);
adapter.notifyItemInserted(12);
} else {
adapter.notifyItemRemoved(0);
adapter.notifyItemRemoved(3);
adapter.notifyItemRemoved(6);
adapter.notifyItemRemoved(9);
adapter.notifyItemRemoved(12);
}
}
int getColumnCount(final int dpThreshold){
final Display display = getWindowManager().getDefaultDisplay();
final DisplayMetrics outMetrics = new DisplayMetrics();
display.getMetrics(outMetrics);
final float density = getResources().getDisplayMetrics().density;
final float dpWidth = outMetrics.widthPixels / density;
return ((int) dpWidth) / dpThreshold;
}
class TestAdapter extends RecyclerView.Adapter {
public static final int TYPE_RED = 0;
public static final int TYPE_GREEN = 1;
public static final int TYPE_BLUE = 2;
private boolean filtered = false;
public boolean isFiltered() {
return filtered;
}
public void setFiltered(final boolean filtered) {
this.filtered = filtered;
}
#Override
public RecyclerView.ViewHolder onCreateViewHolder(final ViewGroup parent, final int viewType) {
final View view = new View(parent.getContext());
view.setLayoutParams(new RelativeLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, 500));
int color = Color.RED;
if(viewType == TYPE_GREEN){
color = Color.GREEN;
} else if (viewType == TYPE_BLUE){
color = Color.BLUE;
}
return new TestViewHolder(view, color);
}
#Override
public void onBindViewHolder(final RecyclerView.ViewHolder holder, final int position) {
}
#Override
public int getItemViewType(final int position) {
if(!filtered) {
if ((position + 3) % 3 == 0) {
return TYPE_RED;
}
if ((position + 2) % 3 == 0) {
return TYPE_GREEN;
}
} else {
if ((position) % 2 == 0) {
return TYPE_GREEN;
}
}
return TYPE_BLUE;
}
#Override
public int getItemCount() {
if(filtered) {
return 10;
}
return 15;
}
class TestViewHolder extends RecyclerView.ViewHolder {
public TestViewHolder(final View itemView, final int color) {
super(itemView);
itemView.setBackgroundColor(color);
}
}
}
}
And here is the layout code:
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/root_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.RecyclerView
android:id="#+id/recycler_view"
android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constraintBottom_toBottomOf="#+id/root_layout"
app:layout_constraintLeft_toLeftOf="#+id/root_layout"
app:layout_constraintRight_toRightOf="#+id/root_layout"
app:layout_constraintTop_toTopOf="#+id/root_layout"/>
<android.support.design.widget.FloatingActionButton
android:id="#+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:layout_constraintBottom_toBottomOf="#+id/root_layout"
app:layout_constraintRight_toRightOf="#+id/root_layout"
android:layout_margin="16dp"
/>
</android.support.constraint.ConstraintLayout>

Firstly, I should mention that the problem is not in DefaultItemAnimator. If you set your animator to null, you would have the same behavior. And actually there is no problem at all. The behavior is expected, as you're just inserting the item into the first position of your TestAdapter, and then other items are shifting, but your RecyclerView is staying at the same position.
So all you need is just add recyclerView.scrollToPosition(0); line in the end of your toggleFiltered() method, so it will scroll up, once you've applied the filtering. And it will work as you wish.

its not weird. because you notifyItemInserted(0). it is insert Item. not notifyDataSetChanged(). adapter is showing item keep going. its Green Item. you notifyItemInserted(0) insert Red, still adapter showing first item is Green(it poisition is 1). because adapter notifyItemInserted(0) has before showing first item is Green.