How to add a fast-scroller to the RecyclerView

Question

Background

On ListView, you could have a fast scroller which allowed you to drag a scrollbar to easily scroll to wherever you wished (using fastScrollEnabled attribute)

Together with "SectionIndexer" class and optionally some attributes, you could have a nice popup that shows as you use this scrollbar (link here).

Such a thing is shown on the contacts app so that you could scroll easily to specific letters.

The problem

RecyclerView doesn't seem to have any of those. Not even a fast-scroll.

The question

How do I add a fast scroller functionality for the RecyclerView?

Answer 1

Just enable fast scrolling and add thumb, tracker for scroll bar like below.

<android.support.v7.widget.RecyclerView
android:id="@+id/rv_sensors"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:fastScrollEnabled="true"
app:fastScrollHorizontalThumbDrawable="@drawable/thumb_drawable"
app:fastScrollHorizontalTrackDrawable="@drawable/line_drawable"
app:fastScrollVerticalThumbDrawable="@drawable/thumb_drawable"
app:fastScrollVerticalTrackDrawable="@drawable/line_drawable" />

Answer 2

There are a lot of unanswered questions about RecyclerView and fast-scroll/section indexer, let's try to regroup and gather our opinions and information here.

The short answer is: NO, you can't enable the fast-scroll because RecyclerView does not contain a FastScroller object and nor any related logical-state variables. This because RecyclerView is not an AbsListView.

On the other hand, it's not impossible to implement a RecyclerView which contains a dumped version of FastScroller and the necessary logic for the fast-scrolling, but I have not seen any implementation of this so far.

Please share your consideration about that or if you think I'm wrong.

Answer 3

The Android Support Library 26.0.0 now supports fastScrollEnabled

New fastScrollEnabled boolean flag for RecyclerView.

If enabled, fastScrollHorizontalThumbDrawable, fastScrollHorizontalTrackDrawable, fastScrollVerticalThumbDrawable, and fastScrollVerticalTrackDrawable must be set.

Sample - https://android.jlelse.eu/fast-scrolling-with-recyclerview-2b89d4574688

Answer 4

There is a provision of implementing scroll bars with RecycleView and its LayoutManager.

For example: computeVerticalScrollExtent() , computeVerticalScrollOffset() and computeVerticalScrollRange() can provide information for always positioning a vertical scroll thumb at correct place.

These methods are also there in LayoutManager for delegating actual measurements. So the LayoutManager implementation used must support these measurements.

Also, drag touch on scroll thumb can be intercepted by overriding onInterceptTouchEvent() of RecyclerView. And after calculating the desired scroll, scrollTo() can be called to update RecyclerView.

Answer 5

Since all third party libraries had issues, I've decided to gather what I can find (mostly from here), fix everything and publish my own POC of the fast-scroller of the RecyclerView :

https://github.com/AndroidDeveloperLB/LollipopContactsRecyclerViewFastScroller

usage:

1. make a RecyclerView.Adapter that implements BubbleTextGetter, which given a position in the data will return the text to show in the bubble-popup.

2. position the FastScroller inside the layout that container the RecyclerView (probably at the right area).

3. Customize the FastScroller FastScroller

Some disadvantages:

1. doesn't support orientation change, but it's probably easy to fix.
2. doesn't support other layoutManagers. Only LinearLayoutManager
3. Needs API 11 and above.

Code:

BubbleTextGetter

public interface BubbleTextGetter
  {
  String getTextToShowInBubble(int pos);
  }

recycler_view_fast_scroller__fast_scroller.xml

<?xml version="1.0" encoding="utf-8"?>
<merge xmlns:android="http://schemas.android.com/apk/res/android"
       xmlns:tools="http://schemas.android.com/tools"
       android:layout_width="wrap_content"
       android:layout_height="match_parent">

  <TextView
    android:id="@+id/fastscroller_bubble"
    android:layout_gravity="right|end"
    android:gravity="center"
    android:textSize="48sp" tools:text="A"
    android:layout_width="wrap_content"
    android:textColor="#FFffffff"
    android:layout_height="wrap_content"
    android:background="@drawable/recycler_view_fast_scroller__bubble"
    android:visibility="visible"/>

  <ImageView
    android:id="@+id/fastscroller_handle"
    android:layout_width="wrap_content"
    android:layout_marginRight="8dp"
    android:layout_marginLeft="8dp"
    android:layout_height="wrap_content"
    android:src="@drawable/recycler_view_fast_scroller__handle"/>

</merge>

MainActivity

...
fastScroller=(FastScroller)findViewById(R.id.fastscroller);
fastScroller.setRecyclerView(recyclerView);

FastScroller

public class FastScroller extends LinearLayout
  {
  private static final int BUBBLE_ANIMATION_DURATION=100;
  private static final int TRACK_SNAP_RANGE=5;

  private TextView bubble;
  private View handle;
  private RecyclerView recyclerView;
  private final ScrollListener scrollListener=new ScrollListener();
  private int height;

  private ObjectAnimator currentAnimator=null;

  public FastScroller(final Context context,final AttributeSet attrs,final int defStyleAttr)
    {
    super(context,attrs,defStyleAttr);
    initialise(context);
    }

  public FastScroller(final Context context)
    {
    super(context);
    initialise(context);
    }

  public FastScroller(final Context context,final AttributeSet attrs)
    {
    super(context,attrs);
    initialise(context);
    }

  private void initialise(Context context)
    {
    setOrientation(HORIZONTAL);
    setClipChildren(false);
    LayoutInflater inflater=LayoutInflater.from(context);
    inflater.inflate(R.layout.recycler_view_fast_scroller__fast_scroller,this,true);
    bubble=(TextView)findViewById(R.id.fastscroller_bubble);
    handle=findViewById(R.id.fastscroller_handle);
    bubble.setVisibility(INVISIBLE);
    }

  @Override
  protected void onSizeChanged(int w,int h,int oldw,int oldh)
    {
    super.onSizeChanged(w,h,oldw,oldh);
    height=h;
    }

  @Override
  public boolean onTouchEvent(@NonNull MotionEvent event)
    {
    final int action=event.getAction();
    switch(action)
      {
      case MotionEvent.ACTION_DOWN:
        if(event.getX()<handle.getX())
          return false;
        if(currentAnimator!=null)
          currentAnimator.cancel();
        if(bubble.getVisibility()==INVISIBLE)
          showBubble();
        handle.setSelected(true);
      case MotionEvent.ACTION_MOVE:
        setPosition(event.getY());
        setRecyclerViewPosition(event.getY());
        return true;
      case MotionEvent.ACTION_UP:
      case MotionEvent.ACTION_CANCEL:
        handle.setSelected(false);
        hideBubble();
        return true;
      }
    return super.onTouchEvent(event);
    }

  public void setRecyclerView(RecyclerView recyclerView)
    {
    this.recyclerView=recyclerView;
    recyclerView.setOnScrollListener(scrollListener);
    }

  private void setRecyclerViewPosition(float y)
    {
    if(recyclerView!=null)
      {
      int itemCount=recyclerView.getAdapter().getItemCount();
      float proportion;
      if(handle.getY()==0)
        proportion=0f;
      else if(handle.getY()+handle.getHeight()>=height-TRACK_SNAP_RANGE)
        proportion=1f;
      else
        proportion=y/(float)height;
      int targetPos=getValueInRange(0,itemCount-1,(int)(proportion*(float)itemCount));
      recyclerView.scrollToPosition(targetPos);
      String bubbleText=((BubbleTextGetter)recyclerView.getAdapter()).getTextToShowInBubble(targetPos);
      bubble.setText(bubbleText);
      }
    }

  private int getValueInRange(int min,int max,int value)
    {
    int minimum=Math.max(min,value);
    return Math.min(minimum,max);
    }

  private void setPosition(float y)
    {
    int bubbleHeight=bubble.getHeight();
    int handleHeight=handle.getHeight();
    handle.setY(getValueInRange(0,height-handleHeight,(int)(y-handleHeight/2)));
    bubble.setY(getValueInRange(0,height-bubbleHeight-handleHeight/2,(int)(y-bubbleHeight)));
    }

  private void showBubble()
    {
    AnimatorSet animatorSet=new AnimatorSet();
    bubble.setVisibility(VISIBLE);
    if(currentAnimator!=null)
      currentAnimator.cancel();
    currentAnimator=ObjectAnimator.ofFloat(bubble,"alpha",0f,1f).setDuration(BUBBLE_ANIMATION_DURATION);
    currentAnimator.start();
    }

  private void hideBubble()
    {
    if(currentAnimator!=null)
      currentAnimator.cancel();
    currentAnimator=ObjectAnimator.ofFloat(bubble,"alpha",1f,0f).setDuration(BUBBLE_ANIMATION_DURATION);
    currentAnimator.addListener(new AnimatorListenerAdapter()
    {
    @Override
    public void onAnimationEnd(Animator animation)
      {
      super.onAnimationEnd(animation);
      bubble.setVisibility(INVISIBLE);
      currentAnimator=null;
      }

    @Override
    public void onAnimationCancel(Animator animation)
      {
      super.onAnimationCancel(animation);
      bubble.setVisibility(INVISIBLE);
      currentAnimator=null;
      }
    });
    currentAnimator.start();
    }

  private class ScrollListener extends OnScrollListener
    {
    @Override
    public void onScrolled(RecyclerView rv,int dx,int dy)
      {
      View firstVisibleView=recyclerView.getChildAt(0);
      int firstVisiblePosition=recyclerView.getChildPosition(firstVisibleView);
      int visibleRange=recyclerView.getChildCount();
      int lastVisiblePosition=firstVisiblePosition+visibleRange;
      int itemCount=recyclerView.getAdapter().getItemCount();
      int position;
      if(firstVisiblePosition==0)
        position=0;
      else if(lastVisiblePosition==itemCount-1)
        position=itemCount-1;
      else
        position=firstVisiblePosition;
      float proportion=(float)position/(float)itemCount;
      setPosition(height*proportion);
      }
    }
  }

Answer 6

I stumbled on this question a few days ago when I ran into this situation. Here is my example implementation of FastScroll for RecyclerView:

github.com/danoz73/RecyclerViewFastScroller

Try running the example application, and peruse the code to see a fairly simple usage of a simple RecyclerViewFastScroller widget. There is information on github, but I'll include the basic usage here for a vertical fast scroller.

For a full example, refer to the sample application in the repo.

Basic Usage

In the activity or fragment XML where your RecyclerView resides, include a VerticalRecyclerViewFastScroller object. The following example would be in a relative layout:

...
  <android.support.v7.widget.RecyclerView
      android:id="@+id/recyclerView"
      android:layout_width="match_parent"
      android:layout_height="match_parent"/>


  <xyz.danoz.recyclerviewfastscroller.vertical.VerticalRecyclerViewFastScroller
      android:id="@+id/fast_scroller"
      android:layout_width="@dimen/however_wide_you_want_this"
      android:layout_height="match_parent"
      android:layout_alignParentRight="true"
    />
...

In your fragment or activity where you setup layout programmatically, hook up the fast scroller to the recycler:

...
  public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
      View rootView = inflater.inflate(R.layout.recycler_view_frag, container, false);
      ...

      // Grab your RecyclerView and the RecyclerViewFastScroller from the layout
      RecyclerView recyclerView = (RecyclerView) rootView.findViewById(R.id.recyclerView);
      VerticalRecyclerViewFastScroller fastScroller = (VerticalRecyclerViewFastScroller) rootView.findViewById(R.id.fast_scroller);

      // Connect the recycler to the scroller (to let the scroller scroll the list)
      fastScroller.setRecyclerView(recyclerView);

      // Connect the scroller to the recycler (to let the recycler scroll the scroller's handle)
      recyclerView.setOnScrollListener(fastScroller.getOnScrollListener());

      ...
      return rootView;
  }
...

Hope this helps!

EDIT: There is now added support for Android-Lollipop-Contacts-style section indicators! Check out the sample application's implementation for details.