How to pass the selected items (multiple items in my recyclerview) values from the adapter to the fragment in android using java

Question

I have a recycler view list in my app. There it has select and unselect option. After selecting the items I need to create a particular item with that selected list.

So I have added the create button in my fragment and showed the selection and unselection in my adapter onBindViewHolder.

Here I need to send the selected item's value to fragment and need to set the post call in the fragment.

My Fragment:

mRecyclerView.setHasFixedSize(true);
mRecyclerView.setAdapter(mAdapter);

        mcreatevendorlist.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                execute(new InitiationRequest("FINTesting", mcreate.getName()), mCreateInitiationListener);
                mAdapter.setOnItemClickListner(new MembersAdapter.onItemClickListner() {
                    @Override
                    public void onClick(User str) {

                    }
                });
            }
        }); 

My Adapter:

  MembersAdapter.onItemClickListner onItemClickListner;
    
     public void setOnItemClickListner(MembersAdapter.onItemClickListner onItemClickListner) {
            this.onItemClickListner = onItemClickListner;
        }
    
        public interface onItemClickListner{
            void onClick(User str);//pass your object types.
        }
    @Override
        public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
            User message = (User) mModelList.get(position);
    
    holder.select_Add.setOnClickListener(new View.OnClickListener() {
                @SuppressLint("ResourceAsColor")
                @Override
                public void onClick(View view) {
                    message.setSelected(!message.isSelected());
                   holder.select_Add.setText(message.isSelected() ? "ADDED" : "Add");
                }
            });
            holder.itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    onItemClickListner.onClick(message);
                }
            });
    }

My mainxml:

 <?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="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/create_vendorlist"
        android:text="Create Vendor"
        android:textColor="@color/black"
        android:background="@drawable/background"
        android:layout_gravity="center"
        android:padding="15dp"
        android:layout_margin="15dp"
        android:textSize="15sp"
        android:fontFamily="@font/cachet_std_medium"
        >
     <androidx.recyclerview.widget.RecyclerView
                android:id="@+id/recycler_view"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:background="@null"/>
    </LinearLayout>

Listview.xml:

       <TextView
            android:id="@+id/tv_username"
            style="@style/Username"
            android:layout_alignParentLeft="@+id/myCardView"
            android:paddingTop="@dimen/spacing_d2"
            tools:text="UserName"/>
        <CheckBox
            android:id="@+id/tv_add"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="onCheckboxClicked"
            android:buttonTint="@color/white"
            android:gravity="center"
            />

Answer 1

First create List to store all selected messages

private final ArrayList<User> selected;

and initialize this array on your Constructor.

Then on on the onBindViewHolder add this method to save the selected or remove the inselected

   User message = (User) mModelList.get(position);
   // rest of your code here 
   holder.checkBox.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                User message = (User) mModelList.get(position);
                if (holder.checkBox.isChecked()){
                    selected.add(message );
                }else{
                    selected.remove(message );
                }
            }
        });

then creat this method on your adapter to access it from the fragment:

 public ArrayList<User> getSelected() {
        return selected;
    }

and on your fragment you can get the selected list when you click on the button :

  btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                ArrayList<User> selectedList=adapter.getSelected();
            }
        });

EDIT

You can also add a boolean named isSelected in your User class like below :

public class User {
    // your variable 
    boolean isSelected;

    
    /*
        rest of setter and getter 
     */
    public boolean isSelected() {
        return isSelected;
    }

    public void setSelected(boolean selected) {
        isSelected = selected;
    }
}

And on your onBindViewHolder add a listener to your check box like this :

  public void onBindViewHolder(@NonNull UserHolder holder, int position) {

        /*
        rest of your code
         */
        holder.checkBox.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                user.setSelected(holder.checkBox.isChecked());
            }
        });
    }

And to get your list add this method in your adapter :

public ArrayList<User> getSelected() {
    ArrayList<User> selected = new ArrayList<>();
    for (User u : modelList) {
        if (u.isSelected) {
            selected.add(u);
        }
    }
    return selected;
}