Why isn't onBindViewHolder getting called when I make a selection?

Question

My scrolling list is displaying properly.

OnBindViewHolder is called for each item in initial display and when scrolling brings new items into view.

When I click on an item, I do see my ItemDetailsLookup and getItemDetails functions getting called, HOWEVER it doesn't call the OnBindViewHolder, and so setActivated isn't getting run.

The documentation for androidx.recyclerview.selection says "... When the user selects an item the library will record that in SelectionTracker then notify RecyclerView that the state of the item has changed. This will ultimately cause the value to be rebound by way of RecyclerView.Adapter#onBindViewHolder..." and I think I've done everything up to this point, but I must have missed something...

Any ideas?

Thanks

Here's my fragment:

package com.example.smartflashcards;

import android.content.Context;
import android.os.Bundle;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.selection.ItemDetailsLookup;
import androidx.recyclerview.selection.SelectionPredicates;
import androidx.recyclerview.selection.SelectionTracker;
import androidx.recyclerview.selection.StableIdKeyProvider;
import androidx.recyclerview.selection.StorageStrategy;
import androidx.recyclerview.widget.GridLayoutManager;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;

import java.io.File;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class StackSelectionFragment extends Fragment {

    private static final String ARG_COLUMN_COUNT = "column-count";
    private int mColumnCount = 1;

    static SelectionTracker<Long> tracker;

    public StackSelectionFragment() {
    }

    @SuppressWarnings("unused")
    public static StackSelectionFragment newInstance(int columnCount) {
        StackSelectionFragment fragment = new StackSelectionFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_COLUMN_COUNT, columnCount);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if (getArguments() != null) {
            mColumnCount = getArguments().getInt(ARG_COLUMN_COUNT);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_stack_selection_list, container, false);
        File directory = getActivity().getFilesDir();

        List<String> filesList = new ArrayList(Arrays.asList(directory.list()));

        if (view instanceof RecyclerView) {
            Context context = view.getContext();
            RecyclerView recyclerView = (RecyclerView) view;
            if (mColumnCount <= 1) {
                recyclerView.setLayoutManager(new LinearLayoutManager(context));
            } else {
                recyclerView.setLayoutManager(new GridLayoutManager(context, mColumnCount));
            }
            recyclerView.setAdapter(new MyItemRecyclerViewAdapter(filesList));
            recyclerView.getAdapter().hasStableIds();

            this.tracker = new SelectionTracker.Builder<Long>(
                    "stack_selector",
                    recyclerView,
                    new StableIdKeyProvider(recyclerView),
                    new MyDetailsLookup(recyclerView),
                    StorageStrategy.createLongStorage()
                ).withSelectionPredicate(SelectionPredicates.<Long>createSelectAnything()).build();
        }
        return view;
    }

    final class MyDetailsLookup extends ItemDetailsLookup {

        private final RecyclerView mRecyclerView;

        MyDetailsLookup(RecyclerView recyclerView) {
            mRecyclerView = recyclerView;
        }

        public @Nullable
        ItemDetails getItemDetails(@NonNull MotionEvent e) {
            View view = mRecyclerView.findChildViewUnder(e.getX(), e.getY());
            if (view != null) {
                RecyclerView.ViewHolder holder = mRecyclerView.getChildViewHolder(view);
                if (holder instanceof MyItemRecyclerViewAdapter.ViewHolder) {
                    return ((MyItemRecyclerViewAdapter.ViewHolder)holder).getItemDetails();
                }
            }
            return null;
        }
    }
}

Here's my adapter:

package com.example.smartflashcards;

import androidx.annotation.Nullable;
import androidx.recyclerview.selection.ItemDetailsLookup;
import androidx.recyclerview.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.ViewGroup;
import android.widget.TextView;

import com.example.smartflashcards.databinding.FragmentStackSelectionBinding;

import java.util.List;

public class MyItemRecyclerViewAdapter extends RecyclerView.Adapter<MyItemRecyclerViewAdapter.ViewHolder> {

    private final List<String> mValues;

    public MyItemRecyclerViewAdapter(List<String> items) {
        setHasStableIds(true);
        mValues = items;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        return new ViewHolder(FragmentStackSelectionBinding.inflate(LayoutInflater.from(parent.getContext()), parent, false));

    }

    @Override
    public void onBindViewHolder(final ViewHolder holder, int position) {
        holder.mItem = getItemId(position);
        holder.mContentView.setText(mValues.get(position));
        holder.mContentView.setActivated(StackSelectionFragment.tracker.isSelected((long) position));
    }

    @Override
    public int getItemCount() {
        return mValues.size();
    }

    @Override
    public long getItemId(int position) {
        return (long)position;
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        public final TextView mIdView;
        public final TextView mContentView;
        public Long mItem;

        public ViewHolder(FragmentStackSelectionBinding binding) {
            super(binding.getRoot());
            mIdView = binding.itemNumber;
            mContentView = binding.content;
        }

        @Override
        public String toString() {
            return super.toString() + " '" + mContentView.getText() + "'";
        }

        public ItemDetailsLookup.ItemDetails<Long> getItemDetails() {
            return new ItemDetailsLookup.ItemDetails<Long>() {
                @Override
                public int getPosition() {
                    return getAbsoluteAdapterPosition();
                }

                @Nullable
                @Override
                public Long getSelectionKey() {
                    return mItem;
                }
            };

        }
    }
}

Answer 1

By following the example at https://github.com/Thumar/recyclerview-selection/tree/master/app I was able to get it working. See my working code below.

But I still don't know which of the changes made it work and why.

If anyone figures out what was causing my problem, please post a comment or answer.

Any and all other feedback is welcome as well.

THANKS

Here's my new fragment:

package com.example.smartflashcards;

import android.content.Context;
import android.os.Bundle;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.selection.ItemDetailsLookup;
import androidx.recyclerview.selection.Selection;
import androidx.recyclerview.selection.SelectionPredicates;
import androidx.recyclerview.selection.SelectionTracker;
import androidx.recyclerview.selection.StableIdKeyProvider;
import androidx.recyclerview.selection.StorageStrategy;
import androidx.recyclerview.widget.GridLayoutManager;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;

import java.io.File;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class StackSelectionFragment extends Fragment {

    // TODO: Customize parameter argument names
    private static final String ARG_COLUMN_COUNT = "column-count";
    // TODO: Customize parameters
    private int mColumnCount = 1;

    SelectionTracker<Long> tracker; //TODO: add private?

    private StackSelectionListener listener;
    public interface StackSelectionListener {
        public void onSelectStack(String stack);
    }

    String selections = "";


    /**
     * Mandatory empty constructor for the fragment manager to instantiate the
     * fragment (e.g. upon screen orientation changes).
     */
    public StackSelectionFragment() {
    }

    // TODO: Customize parameter initialization
    @SuppressWarnings("unused")
    public static StackSelectionFragment newInstance(int columnCount) {
        StackSelectionFragment fragment = new StackSelectionFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_COLUMN_COUNT, columnCount);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if (getArguments() != null) {
            mColumnCount = getArguments().getInt(ARG_COLUMN_COUNT);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_stack_selection_list, container, false);
        File directory = getActivity().getFilesDir();

        List<String> filesList = new ArrayList(Arrays.asList(directory.list()));

        // Set the adapter
        if (view instanceof RecyclerView) {
            Context context = view.getContext();
            RecyclerView recyclerView = (RecyclerView) view;
            if (mColumnCount <= 1) {
                recyclerView.setLayoutManager(new LinearLayoutManager(context));
            } else {
                recyclerView.setLayoutManager(new GridLayoutManager(context, mColumnCount));
            }
            MyItemRecyclerViewAdapter adapter = new MyItemRecyclerViewAdapter(filesList);
            recyclerView.setAdapter(adapter);
            adapter.hasStableIds();

            this.tracker = new SelectionTracker.Builder<Long>(
                    "stack_selector",
                    recyclerView,
                    new StableIdKeyProvider(recyclerView),
                    new MyDetailsLookup(recyclerView),
                    StorageStrategy.createLongStorage()
            ).withSelectionPredicate(SelectionPredicates.<Long>createSelectAnything()).build();
            adapter.injectTracker(this.tracker);

            SelectionTracker.SelectionObserver<Long> observer = new SelectionTracker.SelectionObserver<Long>() {
                @Override
                public void onSelectionChanged() {
                    super.onSelectionChanged();

                    //TODO: replace this placeholder action with something useful
                    selections = "";
                    tracker.getSelection().forEach(item -> selections += adapter.getContent(item.intValue()));//selections += item);
                    //listener.onSelectStack("selections"); //This causes an error???
                    Context context = getContext();
                    Toast toast = Toast.makeText(context, selections, Toast.LENGTH_LONG);
                    toast.show();
                }
            };
            this.tracker.addObserver(observer);
        }
        return view;
    }

    final class MyDetailsLookup extends ItemDetailsLookup {

        private final RecyclerView mRecyclerView;

        MyDetailsLookup(RecyclerView recyclerView) {
            mRecyclerView = recyclerView;
        }

        public @Nullable
        ItemDetails getItemDetails(@NonNull MotionEvent e) {
            View view = mRecyclerView.findChildViewUnder(e.getX(), e.getY());
            if (view != null) {
                RecyclerView.ViewHolder holder = mRecyclerView.getChildViewHolder(view);
                if (holder instanceof MyItemRecyclerViewAdapter.ViewHolder) {
                    return ((MyItemRecyclerViewAdapter.ViewHolder)holder).getItemDetails();
                }
            }
            return null;
        }
    }

Here's my new adapter:

package com.example.smartflashcards;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.recyclerview.selection.ItemDetailsLookup;
import androidx.recyclerview.selection.SelectionTracker;
import androidx.recyclerview.widget.RecyclerView;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.List;

public class MyItemRecyclerViewAdapter extends RecyclerView.Adapter<MyItemRecyclerViewAdapter.ViewHolder> {

    private final List<String> mValues;
    private SelectionTracker<Long> selectionTracker;

    public MyItemRecyclerViewAdapter(List<String> items) {
        setHasStableIds(true); //TODO: remove redundancy between this and "recyclerView.getAdapter().hasStableIds()" in the Fragment
        mValues = items;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fragment_stack_selection, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        String item = this.mValues.get(position);
        holder.bind(item, selectionTracker.isSelected((long) position));
    }

    @Override
    public int getItemCount() {
        return mValues.size();
    }

    @Override
    public long getItemId(int position) {
        return (long)position;
    }

    public String getContent(int position) {
        return mValues.get(position);
    }

    public void injectTracker(SelectionTracker<Long> tracker)
    {
        this.selectionTracker = tracker;
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        public final TextView mContentView;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            mContentView = itemView.findViewById(R.id.content);
        }

        @Override
        public String toString() {
            return super.toString() + " '" + mContentView.getText() + "'";
        }

        public void bind(String item, Boolean activate) {
            this.mContentView.setText(item);
            itemView.setActivated(activate); //TODO: understand how "itemView" exists outside of the constructor
        }

        public ItemDetailsLookup.ItemDetails<Long> getItemDetails() {
            return new ItemDetailsLookup.ItemDetails<Long>() {
                @Override
                public int getPosition() {
                    return getAbsoluteAdapterPosition();
                }

                @Nullable
                @Override
                public Long getSelectionKey() {
                    return (long) getAbsoluteAdapterPosition();
                }
            };
        }
    }
}