car/core/src/main/java/androidx/car/widget/PagedScrollBarView.java - platform/frameworks/support - Git at Google

 /*
  * 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 androidx.car.widget;

 import android.content.Context;
 import android.content.res.Resources;
 import android.content.res.TypedArray;
 import android.graphics.PorterDuff;
 import android.graphics.drawable.Drawable;
 import android.graphics.drawable.GradientDrawable;
 import android.util.AttributeSet;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 import android.view.animation.AccelerateDecelerateInterpolator;
 import android.view.animation.Interpolator;
 import android.widget.ImageView;
 import android.widget.TextView;

 import androidx.annotation.ColorRes;
 import androidx.annotation.DrawableRes;
 import androidx.annotation.IntRange;
 import androidx.annotation.VisibleForTesting;
 import androidx.car.R;
 import androidx.core.content.ContextCompat;

 /** A custom view to provide list scroll behaviour -- up/down buttons and scroll indicator. */
 public class PagedScrollBarView extends ViewGroup {
     private static final float BUTTON_DISABLED_ALPHA = 0.2f;
     private static final int SCROLL_TRANSLATION_ANIM_DURATION_MS = 200;

     /** Listener for when the list should paginate. */
     public interface PaginationListener {
         int PAGE_UP = 0;
         int PAGE_DOWN = 1;

         /** Called when the linked view should be paged in the given direction */
         void onPaginate(int direction);

         /**
          * Called when the 'alpha jump' button is clicked and the linked view should switch into
          * alpha jump mode, where we display a list of buttons to allow the user to quickly scroll
          * to a certain point in the list, bypassing a lot of manual scrolling.
          */
         void onAlphaJump();
     }

     private final ImageView mUpButton;
     private final PaginateButtonClickListener mUpButtonClickListener;
     private final ImageView mDownButton;
     private final PaginateButtonClickListener mDownButtonClickListener;
     private final TextView mAlphaJumpButton;
     private final AlphaJumpButtonClickListener mAlphaJumpButtonClickListener;
     private final View mScrollThumb;

     private final int mSeparatingMargin;
     private final int mScrollBarThumbWidth;

     private boolean mShowScrollBarThumb;
     /** The amount of space that the scroll thumb is allowed to roam over. */
     private int mScrollThumbTrackHeight;

     private final Interpolator mPaginationInterpolator = new AccelerateDecelerateInterpolator();

     public PagedScrollBarView(Context context) {
         this(context, /* attrs= */ null, R.attr.pagedScrollBarViewStyle,
                 R.style.Widget_Car_Scrollbar_Light);
     }

     public PagedScrollBarView(Context context, AttributeSet attrs) {
         this(context, attrs, R.attr.pagedScrollBarViewStyle, R.style.Widget_Car_Scrollbar_Light);
     }

     public PagedScrollBarView(Context context, AttributeSet attrs, int defStyleAttrs) {
         this(context, attrs, defStyleAttrs, R.style.Widget_Car_Scrollbar_Light);
     }

     public PagedScrollBarView(
             Context context, AttributeSet attrs, int defStyleAttrs, int defStyleRes) {
         super(context, attrs, defStyleAttrs, defStyleRes);

         Resources res = context.getResources();
         mSeparatingMargin = res.getDimensionPixelSize(R.dimen.car_padding_4);
         mScrollBarThumbWidth = res.getDimensionPixelSize(R.dimen.car_scroll_bar_thumb_width);

         LayoutInflater.from(context).inflate(R.layout.car_paged_scrollbar_buttons,
                 /* root= */ this, /* attachToRoot= */ true);

         mUpButtonClickListener = new PaginateButtonClickListener(PaginationListener.PAGE_UP);
         mDownButtonClickListener = new PaginateButtonClickListener(PaginationListener.PAGE_DOWN);
         mAlphaJumpButtonClickListener = new AlphaJumpButtonClickListener();

         mUpButton = findViewById(R.id.page_up);
         mUpButton.setOnClickListener(mUpButtonClickListener);
         mDownButton = findViewById(R.id.page_down);
         mDownButton.setOnClickListener(mDownButtonClickListener);
         mAlphaJumpButton = findViewById(R.id.alpha_jump);
         mAlphaJumpButton.setOnClickListener(mAlphaJumpButtonClickListener);
         mScrollThumb = findViewById(R.id.scrollbar_thumb);

         TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.PagedScrollBarView,
                 defStyleAttrs, defStyleRes);

         mShowScrollBarThumb = a.getBoolean(R.styleable.PagedScrollBarView_showScrollBarThumb, true);
         setScrollbarThumbEnabled(mShowScrollBarThumb);
         Drawable upButtonIcon = a.getDrawable(R.styleable.PagedScrollBarView_upButtonIcon);
         if (upButtonIcon != null) {
             setUpButtonIcon(upButtonIcon);
         }

         Drawable downButtonIcon = a.getDrawable(R.styleable.PagedScrollBarView_downButtonIcon);
         if (downButtonIcon != null) {
             setDownButtonIcon(downButtonIcon);
         }

         int scrollBarColor = a.getResourceId(R.styleable.PagedScrollBarView_scrollBarColor, -1);
         if (scrollBarColor != -1) {
             setScrollbarThumbColor(scrollBarColor);
         }

         int buttonTintColor = a.getResourceId(R.styleable.PagedScrollBarView_buttonTintColor, -1);
         if (buttonTintColor != -1) {
             setButtonTintColor(buttonTintColor);
         }

         int buttonRippleBackground =
                 a.getResourceId(R.styleable.PagedScrollBarView_buttonRippleBackground, -1);
         if (buttonRippleBackground != -1) {
             setButtonRippleBackground(buttonRippleBackground);
         }

         a.recycle();
     }

     /** Sets the icon to be used for the up button. */
     public void setUpButtonIcon(Drawable icon) {
         mUpButton.setImageDrawable(icon);
     }

     /** Sets the icon to be used for the down button. */
     public void setDownButtonIcon(Drawable icon) {
         mDownButton.setImageDrawable(icon);
     }

     /**
      * Sets the listener that will be notified when the up and down buttons have been pressed.
      *
      * @param listener The listener to set.
      */
     public void setPaginationListener(PaginationListener listener) {
         mUpButtonClickListener.setPaginationListener(listener);
         mDownButtonClickListener.setPaginationListener(listener);
         mAlphaJumpButtonClickListener.setPaginationListener(listener);
     }

     /** Returns {@code true} if the "up" button is pressed */
     public boolean isUpPressed() {
         return mUpButton.isPressed();
     }

     /** Returns {@code true} if the "down" button is pressed */
     public boolean isDownPressed() {
         return mDownButton.isPressed();
     }

     void setShowAlphaJump(boolean show) {
         mAlphaJumpButton.setVisibility(show ? VISIBLE : GONE);
     }

     /** Returns {@code true} if the scroll bar thumb is visible */
     public boolean isScrollbarThumbEnabled() {
         return mShowScrollBarThumb;
     }
     /**
      * Sets whether or not the scroll bar thumb is visible, the default value is true.
      *
      * @param show {@code true} if the scroll bar thumb is visible.
      */
     public void setScrollbarThumbEnabled(boolean show) {
         mShowScrollBarThumb = show;
         mScrollThumb.setVisibility(mShowScrollBarThumb ? VISIBLE : GONE);
     }

     /**
      * Sets the range, offset and extent of the scroll bar. The range represents the size of a
      * container for the scrollbar thumb; offset is the distance from the start of the container
      * to where the thumb should be; and finally, extent is the size of the thumb.
      *
      * <p>These values can be expressed in arbitrary units, so long as they share the same units.
      * The values should also be positive.
      *
      * @param range The range of the scrollbar's thumb
      * @param offset The offset of the scrollbar's thumb
      * @param extent The extent of the scrollbar's thumb
      * @param animate Whether or not the thumb should animate from its current position to the
      *                position specified by the given range, offset and extent.
      *
      * @see View#computeVerticalScrollRange()
      * @see View#computeVerticalScrollOffset()
      * @see View#computeVerticalScrollExtent()
      */
     public void setParameters(
             @IntRange(from = 0) int range,
             @IntRange(from = 0) int offset,
             @IntRange(from = 0) int extent, boolean animate) {
         // Not laid out yet, so values cannot be calculated.
         if (!isLaidOut()) {
             return;
         }

         // If the scroll bars aren't visible, then no need to update.
         if (getVisibility() == GONE || range == 0) {
             return;
         }

         int thumbLength = calculateScrollThumbLength(range, extent);

         // Sets the size of the thumb and request a redraw if needed.
         ViewGroup.LayoutParams lp = mScrollThumb.getLayoutParams();

         if (lp.height != thumbLength) {
             lp.height = thumbLength;
             mScrollThumb.requestLayout();
         }

         int thumbOffset = calculateScrollThumbOffset(range, offset, thumbLength);
         moveTranslationY(mScrollThumb, thumbOffset, animate);
     }

     /**
      * An optimized version of {@link #setParameters(int, int, int, boolean)} that is meant to be
      * called if a view is laying itself out. This method will avoid a complete remeasure of
      * the views in the {@code PagedScrollBarView} if the scroll thumb's height needs to be changed.
      * Instead, only the thumb itself will be remeasured and laid out.
      *
      * <p>These values can be expressed in arbitrary units, so long as they share the same units.
      *
      * @param range The range of the scrollbar's thumb
      * @param offset The offset of the scrollbar's thumb
      * @param extent The extent of the scrollbar's thumb
      *
      * @see #setParameters(int, int, int, boolean)
      */
     void setParametersInLayout(int range, int offset, int extent) {
         // If the scroll bars aren't visible, then no need to update.
         if (getVisibility() == GONE || range == 0) {
             return;
         }

         int thumbLength = calculateScrollThumbLength(range, extent);

         // Sets the size of the thumb and request a redraw if needed.
         ViewGroup.LayoutParams lp = mScrollThumb.getLayoutParams();

         if (lp.height != thumbLength) {
             lp.height = thumbLength;
             measureAndLayoutScrollThumb();
         }

         int thumbOffset = calculateScrollThumbOffset(range, offset, thumbLength);
         moveTranslationY(mScrollThumb, thumbOffset, /* animate= */ false);
     }

     /**
      * Sets whether or not the up button on the scroll bar is clickable.
      *
      * @param enabled {@code true} if the up button is enabled.
      */
     public void setUpEnabled(boolean enabled) {
         mUpButton.setEnabled(enabled);
         mUpButton.setAlpha(enabled ? 1f : BUTTON_DISABLED_ALPHA);
     }

     /**
      * Sets whether or not the down button on the scroll bar is clickable.
      *
      * @param enabled {@code true} if the down button is enabled.
      */
     public void setDownEnabled(boolean enabled) {
         mDownButton.setEnabled(enabled);
         mDownButton.setAlpha(enabled ? 1f : BUTTON_DISABLED_ALPHA);
     }

     /**
      * Returns whether or not the down button on the scroll bar is clickable.
      *
      * @return {@code true} if the down button is enabled. {@code false} otherwise.
      */
     public boolean isDownEnabled() {
         return mDownButton.isEnabled();
     }

     /**
      * Sets the color of thumb.
      *
      * @param color Resource identifier of the color.
      */
     public void setScrollbarThumbColor(@ColorRes int color) {
         GradientDrawable background = (GradientDrawable) mScrollThumb.getBackground();
         background.setColor(getContext().getColor(color));
     }

     /**
      * Sets the tint color for the up and down buttons of this view.
      *
      * @param tintResId Resource identifier of the tint color.
      */
     public void setButtonTintColor(@ColorRes int tintResId) {
         int tint = ContextCompat.getColor(getContext(), tintResId);
         mUpButton.setColorFilter(tint, PorterDuff.Mode.SRC_IN);
         mDownButton.setColorFilter(tint, PorterDuff.Mode.SRC_IN);
     }

     /**
      * Sets the drawable that will function as the background for the buttons in this view. This
      * background should provide the ripple.
      *
      * @param backgroundResId The drawable resource identifier for the ripple background.
      */
     public void setButtonRippleBackground(@DrawableRes int backgroundResId) {
         mUpButton.setBackgroundResource(backgroundResId);
         mDownButton.setBackgroundResource(backgroundResId);
     }

     @Override
     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
         int requestedWidth = MeasureSpec.getSize(widthMeasureSpec);
         int requestedHeight = MeasureSpec.getSize(heightMeasureSpec);

         int wrapMeasureSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);

         mUpButton.measure(wrapMeasureSpec, wrapMeasureSpec);
         mDownButton.measure(wrapMeasureSpec, wrapMeasureSpec);

         measureScrollThumb();

         if (mAlphaJumpButton.getVisibility() != GONE) {
             mAlphaJumpButton.measure(wrapMeasureSpec, wrapMeasureSpec);
         }

         setMeasuredDimension(requestedWidth, requestedHeight);
     }

     @Override
     public void onLayout(boolean changed, int left, int top, int right, int bottom) {
         int width = right - left;
         int height = bottom - top;

         // This value will keep track of the top of the current view being laid out.
         int layoutTop = getPaddingTop();

         // Lay out the up button at the top of the view.
         layoutViewCenteredFromTop(mUpButton, layoutTop, width);
         layoutTop = mUpButton.getBottom();

         // Lay out the alpha jump button if it exists. This button goes below the up button.
         if (mAlphaJumpButton.getVisibility() != GONE) {
             layoutTop += mSeparatingMargin;

             layoutViewCenteredFromTop(mAlphaJumpButton, layoutTop, width);

             layoutTop = mAlphaJumpButton.getBottom();
         }

         // Lay out the scroll thumb
         layoutTop += mSeparatingMargin;
         layoutViewCenteredFromTop(mScrollThumb, layoutTop, width);

         // Lay out the bottom button at the bottom of the view.
         int downBottom = height - getPaddingBottom();
         layoutViewCenteredFromBottom(mDownButton, downBottom, width);

         calculateScrollThumbTrackHeight();
     }

     /**
      * Calculate the amount of space that the scroll bar thumb is allowed to roam. The thumb
      * is allowed to take up the space between the down bottom and the up or alpha jump
      * button, depending on if the latter is visible.
      */
     private void calculateScrollThumbTrackHeight() {
         // Subtracting (2 * mSeparatingMargin) for the top/bottom margin above and below the
         // scroll bar thumb.
         mScrollThumbTrackHeight = mDownButton.getTop() - (2 * mSeparatingMargin);

         // If there's an alpha jump button, then the thumb is laid out starting from below that.
         if (mAlphaJumpButton.getVisibility() != GONE) {
             mScrollThumbTrackHeight -= mAlphaJumpButton.getBottom();
         } else {
             mScrollThumbTrackHeight -= mUpButton.getBottom();
         }
     }

     private void measureScrollThumb() {
         int scrollWidth = MeasureSpec.makeMeasureSpec(mScrollBarThumbWidth, MeasureSpec.EXACTLY);
         int scrollHeight = MeasureSpec.makeMeasureSpec(
                 mScrollThumb.getLayoutParams().height,
                 MeasureSpec.EXACTLY);
         mScrollThumb.measure(scrollWidth, scrollHeight);
     }

     /**
      * An optimization method to only remeasure and lay out the scroll thumb. This method should be
      * used when the height of the thumb has changed, but no other views need to be remeasured.
      */
     private void measureAndLayoutScrollThumb() {
         measureScrollThumb();

         // The top value should not change from what it was before; only the height is assumed to
         // be changing.
         int layoutTop = mScrollThumb.getTop();
         layoutViewCenteredFromTop(mScrollThumb, layoutTop, getMeasuredWidth());
     }

     /**
      * Lays out the given View starting from the given {@code top} value downwards and centered
      * within the given {@code availableWidth}.
      *
      * @param  view The view to lay out.
      * @param  top The top value to start laying out from. This value will be the resulting top
      *             value of the view.
      * @param  availableWidth The width in which to center the given view.
      */
     private void layoutViewCenteredFromTop(View view, int top, int availableWidth) {
         int viewWidth = view.getMeasuredWidth();
         int viewLeft = (availableWidth - viewWidth) / 2;
         view.layout(viewLeft, top, viewLeft + viewWidth,
                 top + view.getMeasuredHeight());
     }

     /**
      * Lays out the given View starting from the given {@code bottom} value upwards and centered
      * within the given {@code availableSpace}.
      *
      * @param  view The view to lay out.
      * @param  bottom The bottom value to start laying out from. This value will be the resulting
      *                bottom value of the view.
      * @param  availableWidth The width in which to center the given view.
      */
     private void layoutViewCenteredFromBottom(View view, int bottom, int availableWidth) {
         int viewWidth = view.getMeasuredWidth();
         int viewLeft = (availableWidth - viewWidth) / 2;
         view.layout(viewLeft, bottom - view.getMeasuredHeight(),
                 viewLeft + viewWidth, bottom);
     }

     @VisibleForTesting
     int getScrollbarThumbColor() {
         return ((GradientDrawable) mScrollThumb.getBackground()).getColor().getDefaultColor();
     }

     /**
      * Calculates and returns how big the scroll bar thumb should be based on the given range and
      * extent.
      *
      * @param range The total amount of space the scroll bar is allowed to roam over.
      * @param extent The amount of space that the scroll bar takes up relative to the range.
      * @return The height of the scroll bar thumb in pixels.
      */
     private int calculateScrollThumbLength(int range, int extent) {
         // Scale the length by the available space that the thumb can fill.
         return Math.round(((float) extent / range) * mScrollThumbTrackHeight);
     }

     /**
      * Calculates and returns how much the scroll thumb should be offset from the top of where it
      * has been laid out.
      *
      * @param  range The total amount of space the scroll bar is allowed to roam over.
      * @param  offset The amount the scroll bar should be offset, expressed in the same units as
      *                the given range.
      * @param  thumbLength The current length of the thumb in pixels.
      * @return The amount the thumb should be offset from its current to position in pixels.
      */
     private int calculateScrollThumbOffset(int range, int offset, int thumbLength) {
         // Ensure that if the user has reached the bottom of the list, then the scroll bar is
         // aligned to the bottom as well. Otherwise, scale the offset appropriately.
         return isDownEnabled()
                 ? Math.round(((float) offset / range) * mScrollThumbTrackHeight)
                 : mScrollThumbTrackHeight - thumbLength;
     }

     /** Moves the given view's translationY to the specified position. */
     private void moveTranslationY(View view, float translationY, boolean animate) {
         int duration = animate ? SCROLL_TRANSLATION_ANIM_DURATION_MS : 0;
         view.animate()
                 .translationY(translationY)
                 .setDuration(duration)
                 .setInterpolator(mPaginationInterpolator)
                 .start();
     }

     private static class PaginateButtonClickListener implements View.OnClickListener {
         private final int mPaginateDirection;
         private PaginationListener mPaginationListener;

         PaginateButtonClickListener(int paginateDirection) {
             mPaginateDirection = paginateDirection;
         }

         public void setPaginationListener(PaginationListener listener) {
             mPaginationListener = listener;
         }

         @Override
         public void onClick(View v) {
             if (mPaginationListener != null) {
                 mPaginationListener.onPaginate(mPaginateDirection);
             }
         }
     }

     private static class AlphaJumpButtonClickListener implements View.OnClickListener {
         private PaginationListener mPaginationListener;

         AlphaJumpButtonClickListener() {
         }

         public void setPaginationListener(PaginationListener listener) {
             mPaginationListener = listener;
         }

         @Override
         public void onClick(View v) {
             if (mPaginationListener != null) {
                 mPaginationListener.onAlphaJump();
             }
         }

     }
 }
	/*
	* 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 androidx.car.widget;

	import android.content.Context;
	import android.content.res.Resources;
	import android.content.res.TypedArray;
	import android.graphics.PorterDuff;
	import android.graphics.drawable.Drawable;
	import android.graphics.drawable.GradientDrawable;
	import android.util.AttributeSet;
	import android.view.LayoutInflater;
	import android.view.View;
	import android.view.ViewGroup;
	import android.view.animation.AccelerateDecelerateInterpolator;
	import android.view.animation.Interpolator;
	import android.widget.ImageView;
	import android.widget.TextView;

	import androidx.annotation.ColorRes;
	import androidx.annotation.DrawableRes;
	import androidx.annotation.IntRange;
	import androidx.annotation.VisibleForTesting;
	import androidx.car.R;
	import androidx.core.content.ContextCompat;

	/** A custom view to provide list scroll behaviour -- up/down buttons and scroll indicator. */
	public class PagedScrollBarView extends ViewGroup {
	private static final float BUTTON_DISABLED_ALPHA = 0.2f;
	private static final int SCROLL_TRANSLATION_ANIM_DURATION_MS = 200;

	/** Listener for when the list should paginate. */
	public interface PaginationListener {
	int PAGE_UP = 0;
	int PAGE_DOWN = 1;

	/** Called when the linked view should be paged in the given direction */
	void onPaginate(int direction);

	/**
	* Called when the 'alpha jump' button is clicked and the linked view should switch into
	* alpha jump mode, where we display a list of buttons to allow the user to quickly scroll
	* to a certain point in the list, bypassing a lot of manual scrolling.
	*/
	void onAlphaJump();
	}

	private final ImageView mUpButton;
	private final PaginateButtonClickListener mUpButtonClickListener;
	private final ImageView mDownButton;
	private final PaginateButtonClickListener mDownButtonClickListener;
	private final TextView mAlphaJumpButton;
	private final AlphaJumpButtonClickListener mAlphaJumpButtonClickListener;
	private final View mScrollThumb;

	private final int mSeparatingMargin;
	private final int mScrollBarThumbWidth;

	private boolean mShowScrollBarThumb;
	/** The amount of space that the scroll thumb is allowed to roam over. */
	private int mScrollThumbTrackHeight;

	private final Interpolator mPaginationInterpolator = new AccelerateDecelerateInterpolator();

	public PagedScrollBarView(Context context) {
	this(context, /* attrs= */ null, R.attr.pagedScrollBarViewStyle,
	R.style.Widget_Car_Scrollbar_Light);
	}

	public PagedScrollBarView(Context context, AttributeSet attrs) {
	this(context, attrs, R.attr.pagedScrollBarViewStyle, R.style.Widget_Car_Scrollbar_Light);
	}

	public PagedScrollBarView(Context context, AttributeSet attrs, int defStyleAttrs) {
	this(context, attrs, defStyleAttrs, R.style.Widget_Car_Scrollbar_Light);
	}

	public PagedScrollBarView(
	Context context, AttributeSet attrs, int defStyleAttrs, int defStyleRes) {
	super(context, attrs, defStyleAttrs, defStyleRes);

	Resources res = context.getResources();
	mSeparatingMargin = res.getDimensionPixelSize(R.dimen.car_padding_4);
	mScrollBarThumbWidth = res.getDimensionPixelSize(R.dimen.car_scroll_bar_thumb_width);

	LayoutInflater.from(context).inflate(R.layout.car_paged_scrollbar_buttons,
	/* root= / this, / attachToRoot= */ true);

	mUpButtonClickListener = new PaginateButtonClickListener(PaginationListener.PAGE_UP);
	mDownButtonClickListener = new PaginateButtonClickListener(PaginationListener.PAGE_DOWN);
	mAlphaJumpButtonClickListener = new AlphaJumpButtonClickListener();

	mUpButton = findViewById(R.id.page_up);
	mUpButton.setOnClickListener(mUpButtonClickListener);
	mDownButton = findViewById(R.id.page_down);
	mDownButton.setOnClickListener(mDownButtonClickListener);
	mAlphaJumpButton = findViewById(R.id.alpha_jump);
	mAlphaJumpButton.setOnClickListener(mAlphaJumpButtonClickListener);
	mScrollThumb = findViewById(R.id.scrollbar_thumb);

	TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.PagedScrollBarView,
	defStyleAttrs, defStyleRes);

	mShowScrollBarThumb = a.getBoolean(R.styleable.PagedScrollBarView_showScrollBarThumb, true);
	setScrollbarThumbEnabled(mShowScrollBarThumb);
	Drawable upButtonIcon = a.getDrawable(R.styleable.PagedScrollBarView_upButtonIcon);
	if (upButtonIcon != null) {
	setUpButtonIcon(upButtonIcon);
	}

	Drawable downButtonIcon = a.getDrawable(R.styleable.PagedScrollBarView_downButtonIcon);
	if (downButtonIcon != null) {
	setDownButtonIcon(downButtonIcon);
	}

	int scrollBarColor = a.getResourceId(R.styleable.PagedScrollBarView_scrollBarColor, -1);
	if (scrollBarColor != -1) {
	setScrollbarThumbColor(scrollBarColor);
	}

	int buttonTintColor = a.getResourceId(R.styleable.PagedScrollBarView_buttonTintColor, -1);
	if (buttonTintColor != -1) {
	setButtonTintColor(buttonTintColor);
	}

	int buttonRippleBackground =
	a.getResourceId(R.styleable.PagedScrollBarView_buttonRippleBackground, -1);
	if (buttonRippleBackground != -1) {
	setButtonRippleBackground(buttonRippleBackground);
	}

	a.recycle();
	}

	/** Sets the icon to be used for the up button. */
	public void setUpButtonIcon(Drawable icon) {
	mUpButton.setImageDrawable(icon);
	}

	/** Sets the icon to be used for the down button. */
	public void setDownButtonIcon(Drawable icon) {
	mDownButton.setImageDrawable(icon);
	}

	/**
	* Sets the listener that will be notified when the up and down buttons have been pressed.
	*
	* @param listener The listener to set.
	*/
	public void setPaginationListener(PaginationListener listener) {
	mUpButtonClickListener.setPaginationListener(listener);
	mDownButtonClickListener.setPaginationListener(listener);
	mAlphaJumpButtonClickListener.setPaginationListener(listener);
	}

	/** Returns {@code true} if the "up" button is pressed */
	public boolean isUpPressed() {
	return mUpButton.isPressed();
	}

	/** Returns {@code true} if the "down" button is pressed */
	public boolean isDownPressed() {
	return mDownButton.isPressed();
	}

	void setShowAlphaJump(boolean show) {
	mAlphaJumpButton.setVisibility(show ? VISIBLE : GONE);
	}

	/** Returns {@code true} if the scroll bar thumb is visible */
	public boolean isScrollbarThumbEnabled() {
	return mShowScrollBarThumb;
	}
	/**
	* Sets whether or not the scroll bar thumb is visible, the default value is true.
	*
	* @param show {@code true} if the scroll bar thumb is visible.
	*/
	public void setScrollbarThumbEnabled(boolean show) {
	mShowScrollBarThumb = show;
	mScrollThumb.setVisibility(mShowScrollBarThumb ? VISIBLE : GONE);
	}

	/**
	* Sets the range, offset and extent of the scroll bar. The range represents the size of a
	* container for the scrollbar thumb; offset is the distance from the start of the container
	* to where the thumb should be; and finally, extent is the size of the thumb.
	*
	* <p>These values can be expressed in arbitrary units, so long as they share the same units.
	* The values should also be positive.
	*
	* @param range The range of the scrollbar's thumb
	* @param offset The offset of the scrollbar's thumb
	* @param extent The extent of the scrollbar's thumb
	* @param animate Whether or not the thumb should animate from its current position to the
	* position specified by the given range, offset and extent.
	*
	* @see View#computeVerticalScrollRange()
	* @see View#computeVerticalScrollOffset()
	* @see View#computeVerticalScrollExtent()
	*/
	public void setParameters(
	@IntRange(from = 0) int range,
	@IntRange(from = 0) int offset,
	@IntRange(from = 0) int extent, boolean animate) {
	// Not laid out yet, so values cannot be calculated.
	if (!isLaidOut()) {
	return;
	}

	// If the scroll bars aren't visible, then no need to update.
	if (getVisibility() == GONE \|\| range == 0) {
	return;
	}

	int thumbLength = calculateScrollThumbLength(range, extent);

	// Sets the size of the thumb and request a redraw if needed.
	ViewGroup.LayoutParams lp = mScrollThumb.getLayoutParams();

	if (lp.height != thumbLength) {
	lp.height = thumbLength;
	mScrollThumb.requestLayout();
	}

	int thumbOffset = calculateScrollThumbOffset(range, offset, thumbLength);
	moveTranslationY(mScrollThumb, thumbOffset, animate);
	}

	/**
	* An optimized version of {@link #setParameters(int, int, int, boolean)} that is meant to be
	* called if a view is laying itself out. This method will avoid a complete remeasure of
	* the views in the {@code PagedScrollBarView} if the scroll thumb's height needs to be changed.
	* Instead, only the thumb itself will be remeasured and laid out.
	*
	* <p>These values can be expressed in arbitrary units, so long as they share the same units.
	*
	* @param range The range of the scrollbar's thumb
	* @param offset The offset of the scrollbar's thumb
	* @param extent The extent of the scrollbar's thumb
	*
	* @see #setParameters(int, int, int, boolean)
	*/
	void setParametersInLayout(int range, int offset, int extent) {
	// If the scroll bars aren't visible, then no need to update.
	if (getVisibility() == GONE \|\| range == 0) {
	return;
	}

	int thumbLength = calculateScrollThumbLength(range, extent);

	// Sets the size of the thumb and request a redraw if needed.
	ViewGroup.LayoutParams lp = mScrollThumb.getLayoutParams();

	if (lp.height != thumbLength) {
	lp.height = thumbLength;
	measureAndLayoutScrollThumb();
	}

	int thumbOffset = calculateScrollThumbOffset(range, offset, thumbLength);
	moveTranslationY(mScrollThumb, thumbOffset, /* animate= */ false);
	}

	/**
	* Sets whether or not the up button on the scroll bar is clickable.
	*
	* @param enabled {@code true} if the up button is enabled.
	*/
	public void setUpEnabled(boolean enabled) {
	mUpButton.setEnabled(enabled);
	mUpButton.setAlpha(enabled ? 1f : BUTTON_DISABLED_ALPHA);
	}

	/**
	* Sets whether or not the down button on the scroll bar is clickable.
	*
	* @param enabled {@code true} if the down button is enabled.
	*/
	public void setDownEnabled(boolean enabled) {
	mDownButton.setEnabled(enabled);
	mDownButton.setAlpha(enabled ? 1f : BUTTON_DISABLED_ALPHA);
	}

	/**
	* Returns whether or not the down button on the scroll bar is clickable.
	*
	* @return {@code true} if the down button is enabled. {@code false} otherwise.
	*/
	public boolean isDownEnabled() {
	return mDownButton.isEnabled();
	}

	/**
	* Sets the color of thumb.
	*
	* @param color Resource identifier of the color.
	*/
	public void setScrollbarThumbColor(@ColorRes int color) {
	GradientDrawable background = (GradientDrawable) mScrollThumb.getBackground();
	background.setColor(getContext().getColor(color));
	}

	/**
	* Sets the tint color for the up and down buttons of this view.
	*
	* @param tintResId Resource identifier of the tint color.
	*/
	public void setButtonTintColor(@ColorRes int tintResId) {
	int tint = ContextCompat.getColor(getContext(), tintResId);
	mUpButton.setColorFilter(tint, PorterDuff.Mode.SRC_IN);
	mDownButton.setColorFilter(tint, PorterDuff.Mode.SRC_IN);
	}

	/**
	* Sets the drawable that will function as the background for the buttons in this view. This
	* background should provide the ripple.
	*
	* @param backgroundResId The drawable resource identifier for the ripple background.
	*/
	public void setButtonRippleBackground(@DrawableRes int backgroundResId) {
	mUpButton.setBackgroundResource(backgroundResId);
	mDownButton.setBackgroundResource(backgroundResId);
	}

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
	int requestedWidth = MeasureSpec.getSize(widthMeasureSpec);
	int requestedHeight = MeasureSpec.getSize(heightMeasureSpec);

	int wrapMeasureSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);

	mUpButton.measure(wrapMeasureSpec, wrapMeasureSpec);
	mDownButton.measure(wrapMeasureSpec, wrapMeasureSpec);

	measureScrollThumb();

	if (mAlphaJumpButton.getVisibility() != GONE) {
	mAlphaJumpButton.measure(wrapMeasureSpec, wrapMeasureSpec);
	}

	setMeasuredDimension(requestedWidth, requestedHeight);
	}

	@Override
	public void onLayout(boolean changed, int left, int top, int right, int bottom) {
	int width = right - left;
	int height = bottom - top;

	// This value will keep track of the top of the current view being laid out.
	int layoutTop = getPaddingTop();

	// Lay out the up button at the top of the view.
	layoutViewCenteredFromTop(mUpButton, layoutTop, width);
	layoutTop = mUpButton.getBottom();

	// Lay out the alpha jump button if it exists. This button goes below the up button.
	if (mAlphaJumpButton.getVisibility() != GONE) {
	layoutTop += mSeparatingMargin;

	layoutViewCenteredFromTop(mAlphaJumpButton, layoutTop, width);

	layoutTop = mAlphaJumpButton.getBottom();
	}

	// Lay out the scroll thumb
	layoutTop += mSeparatingMargin;
	layoutViewCenteredFromTop(mScrollThumb, layoutTop, width);

	// Lay out the bottom button at the bottom of the view.
	int downBottom = height - getPaddingBottom();
	layoutViewCenteredFromBottom(mDownButton, downBottom, width);

	calculateScrollThumbTrackHeight();
	}

	/**
	* Calculate the amount of space that the scroll bar thumb is allowed to roam. The thumb
	* is allowed to take up the space between the down bottom and the up or alpha jump
	* button, depending on if the latter is visible.
	*/
	private void calculateScrollThumbTrackHeight() {
	// Subtracting (2 * mSeparatingMargin) for the top/bottom margin above and below the
	// scroll bar thumb.
	mScrollThumbTrackHeight = mDownButton.getTop() - (2 * mSeparatingMargin);

	// If there's an alpha jump button, then the thumb is laid out starting from below that.
	if (mAlphaJumpButton.getVisibility() != GONE) {
	mScrollThumbTrackHeight -= mAlphaJumpButton.getBottom();
	} else {
	mScrollThumbTrackHeight -= mUpButton.getBottom();
	}
	}

	private void measureScrollThumb() {
	int scrollWidth = MeasureSpec.makeMeasureSpec(mScrollBarThumbWidth, MeasureSpec.EXACTLY);
	int scrollHeight = MeasureSpec.makeMeasureSpec(
	mScrollThumb.getLayoutParams().height,
	MeasureSpec.EXACTLY);
	mScrollThumb.measure(scrollWidth, scrollHeight);
	}

	/**
	* An optimization method to only remeasure and lay out the scroll thumb. This method should be
	* used when the height of the thumb has changed, but no other views need to be remeasured.
	*/
	private void measureAndLayoutScrollThumb() {
	measureScrollThumb();

	// The top value should not change from what it was before; only the height is assumed to
	// be changing.
	int layoutTop = mScrollThumb.getTop();
	layoutViewCenteredFromTop(mScrollThumb, layoutTop, getMeasuredWidth());
	}

	/**
	* Lays out the given View starting from the given {@code top} value downwards and centered
	* within the given {@code availableWidth}.
	*
	* @param view The view to lay out.
	* @param top The top value to start laying out from. This value will be the resulting top
	* value of the view.
	* @param availableWidth The width in which to center the given view.
	*/
	private void layoutViewCenteredFromTop(View view, int top, int availableWidth) {
	int viewWidth = view.getMeasuredWidth();
	int viewLeft = (availableWidth - viewWidth) / 2;
	view.layout(viewLeft, top, viewLeft + viewWidth,
	top + view.getMeasuredHeight());
	}

	/**
	* Lays out the given View starting from the given {@code bottom} value upwards and centered
	* within the given {@code availableSpace}.
	*
	* @param view The view to lay out.
	* @param bottom The bottom value to start laying out from. This value will be the resulting
	* bottom value of the view.
	* @param availableWidth The width in which to center the given view.
	*/
	private void layoutViewCenteredFromBottom(View view, int bottom, int availableWidth) {
	int viewWidth = view.getMeasuredWidth();
	int viewLeft = (availableWidth - viewWidth) / 2;
	view.layout(viewLeft, bottom - view.getMeasuredHeight(),
	viewLeft + viewWidth, bottom);
	}

	@VisibleForTesting
	int getScrollbarThumbColor() {
	return ((GradientDrawable) mScrollThumb.getBackground()).getColor().getDefaultColor();
	}

	/**
	* Calculates and returns how big the scroll bar thumb should be based on the given range and
	* extent.
	*
	* @param range The total amount of space the scroll bar is allowed to roam over.
	* @param extent The amount of space that the scroll bar takes up relative to the range.
	* @return The height of the scroll bar thumb in pixels.
	*/
	private int calculateScrollThumbLength(int range, int extent) {
	// Scale the length by the available space that the thumb can fill.
	return Math.round(((float) extent / range) * mScrollThumbTrackHeight);
	}

	/**
	* Calculates and returns how much the scroll thumb should be offset from the top of where it
	* has been laid out.
	*
	* @param range The total amount of space the scroll bar is allowed to roam over.
	* @param offset The amount the scroll bar should be offset, expressed in the same units as
	* the given range.
	* @param thumbLength The current length of the thumb in pixels.
	* @return The amount the thumb should be offset from its current to position in pixels.
	*/
	private int calculateScrollThumbOffset(int range, int offset, int thumbLength) {
	// Ensure that if the user has reached the bottom of the list, then the scroll bar is
	// aligned to the bottom as well. Otherwise, scale the offset appropriately.
	return isDownEnabled()
	? Math.round(((float) offset / range) * mScrollThumbTrackHeight)
	: mScrollThumbTrackHeight - thumbLength;
	}

	/** Moves the given view's translationY to the specified position. */
	private void moveTranslationY(View view, float translationY, boolean animate) {
	int duration = animate ? SCROLL_TRANSLATION_ANIM_DURATION_MS : 0;
	view.animate()
	.translationY(translationY)
	.setDuration(duration)
	.setInterpolator(mPaginationInterpolator)
	.start();
	}

	private static class PaginateButtonClickListener implements View.OnClickListener {
	private final int mPaginateDirection;
	private PaginationListener mPaginationListener;

	PaginateButtonClickListener(int paginateDirection) {
	mPaginateDirection = paginateDirection;
	}

	public void setPaginationListener(PaginationListener listener) {
	mPaginationListener = listener;
	}

	@Override
	public void onClick(View v) {
	if (mPaginationListener != null) {
	mPaginationListener.onPaginate(mPaginateDirection);
	}
	}
	}

	private static class AlphaJumpButtonClickListener implements View.OnClickListener {
	private PaginationListener mPaginationListener;

	AlphaJumpButtonClickListener() {
	}

	public void setPaginationListener(PaginationListener listener) {
	mPaginationListener = listener;
	}

	@Override
	public void onClick(View v) {
	if (mPaginationListener != null) {
	mPaginationListener.onAlphaJump();
	}
	}

	}
	}