java/com/android/dialer/contactsfragment/FastScroller.java

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.dialer.contactsfragment;

import android.content.Context;
import android.support.annotation.NonNull;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.widget.RelativeLayout;
import android.widget.TextView;

/** Widget to add fast scrolling to {@link ContactsFragment}. */
public class FastScroller extends RelativeLayout {

  private final int touchTargetWidth;

  private ContactsAdapter adapter;
  private LinearLayoutManager layoutManager;

  private TextView container;
  private View scrollBar;

  private boolean dragStarted;

  public FastScroller(Context context, AttributeSet attrs) {
    super(context, attrs);
    touchTargetWidth =
        context.getResources().getDimensionPixelSize(R.dimen.fast_scroller_touch_target_width);
  }

  @Override
  protected void onFinishInflate() {
    super.onFinishInflate();
    container = findViewById(R.id.fast_scroller_container);
    scrollBar = findViewById(R.id.fast_scroller_scroll_bar);
  }

  void setup(ContactsAdapter adapter, LinearLayoutManager layoutManager) {
    this.adapter = adapter;
    this.layoutManager = layoutManager;
    setVisibility(VISIBLE);
  }

  @Override
  public boolean onTouchEvent(@NonNull MotionEvent event) {
    // Don't override if touch event isn't within desired touch target and dragging hasn't started.
    if (!dragStarted && getWidth() - touchTargetWidth - event.getX() > 0) {
      return super.onTouchEvent(event);
    }

    switch (event.getAction()) {
      case MotionEvent.ACTION_DOWN:
        dragStarted = true;
        container.setVisibility(VISIBLE);
        scrollBar.setSelected(true);
        // fall through
      case MotionEvent.ACTION_MOVE:
        setContainerAndScrollBarPosition(event.getY());
        setRecyclerViewPosition(event.getY());
        return true;
      case MotionEvent.ACTION_UP:
      case MotionEvent.ACTION_CANCEL:
        dragStarted = false;
        container.setVisibility(INVISIBLE);
        scrollBar.setSelected(false);
        return true;
    }
    return super.onTouchEvent(event);
  }

  private void setRecyclerViewPosition(float y) {
    final int itemCount = adapter.getItemCount();
    float scrolledPosition = getScrolledPercentage(y) * (float) itemCount;
    int targetPos = getValueInRange(0, itemCount - 1, (int) scrolledPosition);
    layoutManager.scrollToPositionWithOffset(targetPos, 0);
    container.setText(adapter.getHeaderString(targetPos));
  }

  // Returns a float in range [0, 1] which represents the position of the scroller.
  private float getScrolledPercentage(float y) {
    if (scrollBar.getY() == 0) {
      return 0f;
    } else if (scrollBar.getY() + scrollBar.getHeight() >= getHeight()) {
      return 1f;
    } else {
      return y / (float) getHeight();
    }
  }

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

  void updateContainerAndScrollBarPosition(RecyclerView recyclerView) {
    if (!scrollBar.isSelected()) {
      int verticalScrollOffset = recyclerView.computeVerticalScrollOffset();
      int verticalScrollRange = recyclerView.computeVerticalScrollRange();
      float proportion = (float) verticalScrollOffset / ((float) verticalScrollRange - getHeight());
      setContainerAndScrollBarPosition(getHeight() * proportion);
    }
  }

  private void setContainerAndScrollBarPosition(float y) {
    int scrollBarHeight = scrollBar.getHeight();
    int containerHeight = container.getHeight();
    scrollBar.setY(
        getValueInRange(0, getHeight() - scrollBarHeight, (int) (y - scrollBarHeight / 2)));
    container.setY(
        getValueInRange(
            0, getHeight() - containerHeight - scrollBarHeight / 2, (int) (y - containerHeight)));
  }
}