Sectioned RecyclerView with pinnable (floating/sticky) headers

This library allows you to divide items in your RecyclerView into groups called sections. Each section is represented by an adapter and can have a header. SectionAdapter is similar to Android’s RecyclerView.Adapter, which creates and binds ViewHolders. The header can be pinned, which means, that it will be displayed at the top of the RecyclerView above the corresponding section items. Pinned headers change automatically while scrolling or after dataset changes. You can also customize item swiping behavior for each section individually.

Demo

You can find demo project code here.

Advantages

Simplicilty. Classes provided by this library are similar to Android ones.
Flexibility. Your RecyclerView stays compatible with almost any external third-party library or API.
Floating headers feature. An iOS style floating header behaves the same way as an item in the RecyclerView, so you don't have to handle the interaction with it separately.
Swiping feature. You can customize item swiping behavior for each section individually.
ViewHolders reusing. List item ViewHolders are reused as usual, pinned headers are cached and reused with the help of own implementation.

Usage

Setup

The Gradle dependency is available via jCenter. Add this to your module's build.gradle file:

implementation 'com.cruxlab:sectionedrecyclerview:1.0.3'

Initialization

Initialize your RecyclerView with a successor of LinearLayoutManager:

RecyclerView recyclerView = findViewById(R.id.recycler_view);
LinearLayoutManager layoutManager = new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);
recyclerView.setLayoutManager(layoutManager);
recyclerView.setHasFixedSize(false);

Create SectionDataManager and set its adapter to the RecyclerView:

SectionDataManager sectionDataManager = new SectionDataManager();
RecyclerView.Adapter adapter = sectionDataManager.getAdapter();
recyclerView.setAdapter(adapter);

After that you can use SectionDataManager that implements SectionManager interface to add/remove/replace sections in your RecyclerView.

sectionDataManager.addSection(new MySimpleAdapter());
int cnt = sectionDataManager.getSectionCount();
sectionDataManager.removeSection(cnt - 1);

Adapters

This is an example of an adapter for a simple section without header:

public class MySimpleAdapter extends SimpleSectionAdapter<MyItemViewHolder> {

    private ArrayList<String> items = new ArrayList<>(Arrays.asList("First", "Second", "Third"));
    
    @Override
    public int getItemCount() {
        return items.size();
    }

    @Override
    public MyItemViewHolder onCreateItemViewHolder(ViewGroup parent, short type) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_vh_layout, parent, false);
        return new MyItemViewHolder(view);
    }

    @Override
    public void onBindItemViewHolder(MyItemViewHolder holder, int position) {
        holder.bindItem(items.get(position));
    }
}

It uses the following ItemViewHolder:

public class MyItemViewHolder extends BaseSectionAdapter.ItemViewHolder {

    public TextView textView;

    public MyItemViewHolder(View itemView) {
        super(itemView);
        this.textView = itemView.findViewById(R.id.text_view);
    }

    public void bindItem(String text) {
        textView.setText(text);
    }

}

As you can see, these classes are similar to Android’s RecyclerView.Adapter and RecyclerView.ViewHolder.

Adapter for a section with header has some additional methods to override:

public class MyAdapter extends SectionAdapter<MyItemViewHolder, MyHeaderViewHolder> {

    /* Similar methods */

    public MyAdapter(boolean isHeaderVisible, boolean isHeaderPinned) {
        super(isHeaderVisible, isHeaderPinned);
    }

    @Override
    public MyHeaderViewHolder onCreateHeaderViewHolder(ViewGroup parent) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.header_vh_layout, parent, false);
        return new MyHeaderViewHolder(view);
    }

    @Override
    public void onBindHeaderViewHolder(MyHeaderViewHolder holder) {
        holder.bindHeader();
    }
}

When different sections have the same header (HeaderViewHolder and its view), it can be reused by the RecyclerView. To indicate it, you should pass equal header types to the SectionDataManager when adding your SectionAdapter and different ones otherwise:

sectionDataManager.addSection(new MyAdapter(true, true), HEADER_TYPE);
sectionDataManager.addSection(new AdapterWithTheSameHeader(false, false), HEADER_TYPE);
sectionDataManager.insertSection(0, new AdapterWithDifferentHeader(true, false), ANOTHER_HEADER_TYPE);

Floating headers

To use floating headers feature, you have to place your RecyclerView into SectionHeaderLayout in your xml file:

<com.cruxlab.sectionedrecyclerview.lib.SectionHeaderLayout
        android:id="@+id/section_header_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <android.support.v7.widget.RecyclerView
            android:id="@+id/recycler_view"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
            
 </com.cruxlab.sectionedrecyclerview.lib.SectionHeaderLayout>

To enable displaying pinned headers, attach SectionHeaderLayout to your RecyclerView and SectionDataManager:

SectionHeaderLayout sectionHeaderLayout = findViewById(R.id.section_header_layout);
sectionHeaderLayout.attachTo(recyclerView, sectionDataManager);

Now you can manage header pinned state with your adapter:

myAdapter.updateHeaderPinnedState(true);

You can disable disaplying pinned headers any time by calling:

sectionHeaderLayout.detach();

Note, that you should NOT update header view contents manually (e.g., while handling click event), because when header is pinned to the top, its view is duplicated and these changes won't affect the original item in the RecyclerView. You should call notifyHeaderChanged() instead to guarantee that your changes will be applied to both views while binding.

Swiping behavior

You can customize item swiping behavior for each section individually. To enable this feature, create ItemTouchHelper initialized with SectionDataManager's callback and attach it to your RecyclerView:

ItemTouchHelper.Callback callback = sectionDataManager.getSwipeCallback();
ItemTouchHelper itemTouchHelper = new ItemTouchHelper(callback);
itemTouchHelper.attachToRecyclerView(recyclerView);

Implement SectionItemSwipeCallback, which is similar to Android's ItemTouchHelper.Callback:

public class MySwipeCallback extends SectionItemSwipeCallback {

    private ColorDrawable background;

    public DemoSwipeCallback() {
        this.background = new ColorDrawable();
    }

    @Override
    public int getSwipeDirFlags(RecyclerView recyclerView, BaseSectionAdapter.ItemViewHolder viewHolder) {
        return ItemTouchHelper.LEFT;
    }

    @Override
    public void onSwiped(BaseSectionAdapter.ItemViewHolder viewHolder, int direction) {
        // Do something
        MyItemViewHolder itemViewHolder = (MyItemViewHolder) viewHolder;
        int sectionPos = itemViewHolder.getSectionAdapterPosition();
        // This method can return -1 when getAdapterPosition() of the corresponding
        // RecyclerView.ViewHolder returns -1 or when this ViewHolder isn't used
        // in any RecyclerView.
        if (sectionPos == -1) return;
        System.out.println("Swiped item on position " +  sectionPos);
    }

    @Override
    public void onChildDraw(Canvas c, RecyclerView recyclerView, BaseSectionAdapter.ItemViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
        // Draw something on canvas
        View itemView = viewHolder.itemView;
        background.setColor(Color.RED);
        background.setBounds((int) (itemView.getRight() + dX), itemView.getTop(), itemView.getRight(), itemView.getBottom());
        background.draw(c);
        super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
    }

}

You can specify it when adding a section or set/remove it later via SectionDataManager:

sectionDataManager.addSection(new MySimpleAdapter(), new MySwipeCallback());
sectionDataManager.removeSwipeCallback(0);

Note, that section headers are unswipeable.

GridLayoutManager

When using GridLayoutManager set SpanSizeLookup as follows to display full width section headers:

gridLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
    @Override
    public int getSpanSize(int position) {
        if (posManager.isHeader(position)) {
            return gridLayoutManager.getSpanCount();
        } else {
            return 1;
        }
    }
 });

It uses SectionDataManager's implementation of PositionManager to determine whether the item at the given position is a header.

Extra

The number of sections you can add to the SectionDataManager during its lifetime is limited to 32,767.
Sections added via SectionDataManager are indexed beginning with the zero subscript and can be accessed by their index later.
Any ViewHolder can call getGlobalAdapterPosition() or getGlobalLayoutPosition() to access its positions in the global RecyclerView adapter among items of all sections including their headers. It also can get the index of the section it belongs to, which is calculated based on the adapter position, calling getSection().
ItemViewHolder can retrieve its position in the corresponding adapter by calling getSectionAdapterPosition(). The methods above can return -1 when the ViewHolder is not used in any RecyclerView.
For compatibility with future Android RecyclerView APIs and other libraries you can use PositionManager interface to manage positions (e.g., retrieved from real ViewHolder) yourself.

License

This project is licensed under the MIT License - see the LICENSE file for details.

Made with ❤️ by Elizabeth Popova

Contact me: elizaveta.popova@cruxlab.com

madmax3365/sectioned-recycler-view