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.
RecyclerView doesn't seem to have any of those. Not even a fast-scroll.
How do I add a fast scroller functionality for the RecyclerView?
New answer: Over time I've noticed that my original answer had some drawbacks compared to other solutions, especially for fragments within ViewPager.
I suggest to either use the android-x solution in case you don't need a bubble, or a third party library (here is a nice one) in case you do.
old answer:
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:
make a RecyclerView.Adapter that implements BubbleTextGetter, which given a position in the data will return the text to show in the bubble-popup.
position the FastScroller inside the layout that container the RecyclerView (probably at the right area).
Customize the FastScroller FastScroller
Some disadvantages:
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);
}
}
}