FastScroller.java

/*

    Sunami - An Android music player which knows what you want to listen to.
    Copyright (C) 2015 Wojtek Swiderski

    Sunami is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    Sunami is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    The GNU General Public License can be found at the root of this repository.

    To contact me, email me at wojtek.technology@gmail.com

 */

package com.wojtechnology.sunami;

import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.animation.AnimatorSet;
import android.animation.ObjectAnimator;
import android.content.Context;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.widget.LinearLayout;
import android.widget.TextView;

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.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 = ((ListAdapter) 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 RecyclerView.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);
        }
    }
}