Why do we use something like this to populate the recyclerview with data? Can't we just create a simple array of string like String[] titles and display them, like in ListView?
List< Information> data
public void onBindViewHolder(MyViewHolder holder, int position) {
Information current = data.get(position);
holder.title.setText(current.title);
holder.icon.setImageResource(current.iconId);
}
I recently watched a video on how to work with recyclerview and I can't understand why we have to create another class of information and then again create its array inside onBindViewHolder to show data.
Can anybody help me understand this code?
If you take a look at this example by google, they used an array dataset to populate data in RecyclerView.
Take a look at Google's docs:
Called by RecyclerView to display the data at the specified position. This method should update the contents of the itemView to reflect the item at the given position.
Note that unlike ListView, RecyclerView will not call this method again if the position of the item changes in the data set unless the item itself is invalidated or the new position cannot be determined. For this reason, you should only use the position parameter while acquiring the related data item inside this method and should not keep a copy of it. If you need the position of an item later on (e.g. in a click listener), use getAdapterPosition() which will have the updated adapter position. Override onBindViewHolder(ViewHolder, int, List) instead if Adapter can handle effcient partial bind.
String [] title ;
int [] imageID;
onBindViewHolder(MyViewHolder holder, int position) {
Information current = data.get(position);
holder.title.setText(title [position]); holder.icon.setImageResource(imageID [position]);
}
Related
I'm getting the list of user ids from database. And its getting the values correctly. I'm using FirebaseRecyclerAdapter and when I iterate that list in onBindViewHolder the loops runs as the size of list. For example over here :
adapter = new FirebaseRecyclerAdapter<Profiles, DonarViewHolder>(model) {
#Override
protected void onBindViewHolder(#NonNull DonarViewHolder holder, int position, #NonNull Profiles profiles) {
for (int i = 0 ; i<list.size() ; i++){
Toast.makeText(List.this,"List :" +list.get(i), Toast.LENGTH_SHORT).show();
}
}
}
Over here I have 5 item in list and while iterating I'm toasting each item . So in here the loop run for 25 time, its shows each item 5 time in sequence. First it shows 5 items orderly after showing last item it start toasting from first one again and continues till 5 time as the size of list.
So how do I cater this and make it only iterate the whole items for once only?
onBindViewHolder is called by RecyvlerView to display the data at the specified position. Since you have all the data in a List, their corresponding index will be the same as the position of the itemView.
In your function, you are iterating over all the items in the list for each itemView which the ViewHolder is generating.
You have to remove the for loop from your code and simply use the position as the index to retrieve data from your list, whose index is same as position.
Try this code:
adapter = new FirebaseRecyclerAdapter<Profiles, DonarViewHolder>(model) {
#Override
protected void onBindViewHolder(#NonNull DonarViewHolder holder, int position, #NonNull Profiles profiles) {
Toast.makeText(List.this,"List :" +list.get(position), Toast.LENGTH_SHORT).show();
}
}
For this method, every time an itemView is generated, it will be at a position and with this as an index, you can easily get the data from the list.
For your scenario, since you are already inside each itemView being generated inside the onBindViewHolder, and then you are iterating for each element in your list, hence every item is being displayed exactly the same number of times, as the size of the list.
I think you are missing a method that you can use to call each item individually.
create a setter and getter for your item. In your loop you can then call it list.get(position).getItem .
In the list view, I have the object of my POJO class so if I want to fetch an object's position in the list view it can get by below code
mAdapter.getPosition(object)
but I cannot find any solution to get an Adapter position with the help of my object in the recyclerview
Please help me for the same.
You can't get the position via mAdapter.getPosition(object) in case of recycler view. But if you really want the position via object then, you can get it by:
array.indexOf(obj);
here array is your array list which content you are setting to the recycler view.
Use last param of onBindViewHolder() method of Adapter class for get position
public void onBindViewHolder(#NonNull FavourtieViewHolder favourtieViewHolder, int position) {
// like this
POJO obj=list.get(position);
// using Adapter holder class object you can also get position
int pos=favourtieViewHolder.getAdapterPosition();
}
I have a Recycler View in which single row contains several views, including video, like statistic, and a button.
The button is to increment the value of like statistic to that item and update my adapter using notifyItemChange for that position.
My Problem is, while that row gets refreshed and updates my statistic, the video will reset and I will have to load the data from the beginning again.
What I want is like Facebook app, where user add emotion for a single row item, but the View (the video) does not get refreshed, and only certain items are refreshed, like the emotion statistics.
You should consider using
void notifyItemChanged (int position,Object payload)
and capture the payload in
void onBindViewHolder (VH holder,int position, List<Object> payloads)
Based on the payloads parsed in, you can refresh part of your view in the ViewHolder
#Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position, List<Object> payloads) {
if(payloads == null || payloads.isEmpty()) {
onBindViewHolder(holder, position);//your normal method
}
else {
//partial refresh
}
}
You have to make use of payloads. This means, when notifying the adapter about dataset changes, you also are passing payloads, and this payload is being passed to appropriate callback within adapter, where you decide what view's need to be invalidated.
adapter.notifyItemChanged(position, payload); // payload is an Object
And you'll receive this payload in onBindViewHolder of adapter:
public void onBindViewHolder(HelloViewHolder holder, int position, List<Object> payload) {
// decide what to update based on the payload
}
You can view this as an example.
I want to update a view of the recyclerview when a notifyItemChanged has been called. The thing is that I don't want to refresh the entire row but only the view of the row. (to avoid the blinking effect of the row)
There is a method called notifyItemChanged(int, payload obj).
Can I use that to achieve that? If so how to do it?
Finally I found how to update only the specific view of a row in RecyclerView.
(1) Override onBindViewHolder(Recycler.ViewHolder VH, int position, List payloads) in the adapter
(2) Inside that onBindViewHolder method,
if(payloads != null && !payloads.isEmpty() && (payloads.get(0) instanceof customObject)){
// update the specific view
}else{
// I have already overridden the other onBindViewHolder(ViewHolder, int)
// The method with 3 arguments is being called before the method with 2 args.
// so calling super will call that method with 2 arguments.
super.onBindViewHolder(holder,position,payloads);
}
(3) So to notify data change and update the view, need to call the notifyItemChanged(int position, Object payload). Need to pass the customObject(model which holds the data) as the payload object.
adapter.notifyItemChanged(i, obj);
Note : Need to disable the RecyclerView's ItemAnimator(By default it is enabled). Otherwise payload object will be empty.
recyclerView.setItemAnimator(null);
or
((SimpleItemAnimator)recyclerView.getItemAnimator()).setSupportsChangeAnimations(false);
UPDATE: I used this method recently without disabling the ItemAnimator. So no need to disable ItemAnimator. - (recyclerview-v7:25.4.0)
for further reference
You can use this to get the view of updated item:
View v = recyclerView.getLayoutManager().findViewByPosition(position);
if (v != null){
//update your view
}
Let's say you have an ArrayList of items, and it is fed to the RecyclerView adapter. Let it be something like this.
List<String> items = new ArrayList<>();
RecyclerAdapter adapter = new RecyclerAdapter(items);
recyclerView.setAdapter(adapter);
Now as I can see you want to insert items into the RecyclerView and call notifyItemChanged(int position) method to add only the single item.
For this let's say you have changed the value of item in position 0. That's the first item in the list.
Now the proper usage of the method notifyItemChanged(int position) will be
adapter.notifyItemChanged(0);
This means, the adapter will update the recyclerview with the new value in 0 position.
I have a recyclerView in which i have a list of items displayed in a LinearLayout.There is a "increase" button in every list which will increment a quantity by "1".But when I click the button on the first list item to increment the number..the incremented value is displayed in the last list item of the recyclerView not in the desired position where i clicked.Can anyone help me find the solution?
#Override
public void onBindViewHolder(MyViewHolder holder, int position) {
myholder = holder;
holder.item_name_text.setText(data.get(position).getName());
holder.item_price_text.setText(data.get(position).getPrice().toString());
holder.item_quantity_text.setText("500");
//Adding item to the cart
holder.add_image.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(totalItem>=0 && totalItem<10){
totalItem++;
myholder.item_totalquantity_text.setText(String.valueOf(totalItem));
}else{
Toast.makeText(myholder.itemView.getContext(),"Cannot add more item",Toast.LENGTH_SHORT).show();
}
}
});
So I always think of recyclerviews as the frontend that displays my data. If you would like to make changes to the actual data itself and make sure it gets reflected in the recyclerview, you will need to ensure the changes are made inside the arraylist of data objects.
You will need to add a field inside the data object and call it counter. Then you must increment the counter once the user clicks on the onClickListener.
myholder.item_totalquantity_text.setText(data.get(position).setCounter(data.get(position).getCounter())+1);
Do not set OnClickListener() in onBindViewHolder(). Instead do it in your ViewHolder class itself. And main ly as RecyclerView re-uses the holder objects to represent the new set of data that is becoming visible. So the listener on which yo click might be belonging to some other view holder so it appears there instead.
Have a quick read of this and this. These are not very relevant to you but it has info to understnad recycling concept so you can fix your stuff easily.