src/com/android/wallpaper/widget/PreviewPager.java - LeafOS-Project/android_packages_apps_WallpaperPicker2 - Gitiles

 /*
  * Copyright (C) 2018 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.wallpaper.widget;

 import android.content.Context;
 import android.content.res.Resources;
 import android.content.res.TypedArray;
 import android.database.DataSetObserver;
 import android.graphics.Point;
 import android.util.AttributeSet;
 import android.util.Log;
 import android.util.TypedValue;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.WindowManager;
 import android.view.animation.Interpolator;
 import android.widget.LinearLayout;
 import android.widget.Scroller;

 import androidx.annotation.Nullable;
 import androidx.core.text.TextUtilsCompat;
 import androidx.core.view.ViewCompat;
 import androidx.interpolator.view.animation.LinearOutSlowInInterpolator;
 import androidx.viewpager.widget.PagerAdapter;
 import androidx.viewpager.widget.ViewPager;
 import androidx.viewpager.widget.ViewPager.OnPageChangeListener;

 import com.android.wallpaper.R;
 import com.android.wallpaper.util.ScreenSizeCalculator;

 import java.lang.reflect.Field;
 import java.util.Locale;

 /**
  * A Widget consisting of a ViewPager linked to a PageIndicator and previous/next arrows that can be
  * used to page over that ViewPager.
  * To use it, set a {@link PagerAdapter} using {@link #setAdapter(PagerAdapter)}, and optionally use
  * a {@link #setOnPageChangeListener(OnPageChangeListener)} to listen for page changes.
  */
 public class PreviewPager extends LinearLayout {

     private static final String TAG = "PreviewPager";
     private static final int STYLE_PEEKING = 0;
     private static final int STYLE_ASPECT_RATIO = 1;

     private final ViewPager mViewPager;
     private final PageIndicator mPageIndicator;
     private final View mPreviousArrow;
     private final View mNextArrow;
     private final ViewPager.OnPageChangeListener mPageListener;
     private int mPageStyle;

     private PagerAdapter mAdapter;
     private ViewPager.OnPageChangeListener mExternalPageListener;
     private float mScreenAspectRatio;
     /** The maximum height ratio of PreviewPager and its parent view. */
     private float mMaxHeightRatio;

     public PreviewPager(Context context) {
         this(context, null);
     }

     public PreviewPager(Context context, AttributeSet attrs) {
         this(context, attrs, 0);
     }

     public PreviewPager(Context context, AttributeSet attrs, int defStyleAttr) {
         super(context, attrs, defStyleAttr);
         LayoutInflater.from(context).inflate(R.layout.preview_pager, this);
         Resources res = context.getResources();
         TypedArray a = context.obtainStyledAttributes(attrs,
                 R.styleable.PreviewPager, defStyleAttr, 0);

         mPageStyle = a.getInteger(R.styleable.PreviewPager_card_style, STYLE_PEEKING);

         a.recycle();

         TypedValue ratioValue = new TypedValue();
         res.getValue(R.dimen.preview_pager_maximum_height_ratio, ratioValue, true);
         mMaxHeightRatio = ratioValue.getFloat();

         mViewPager = findViewById(R.id.preview_viewpager);
         mViewPager.setPageTransformer(false, (view, position) -> {
             int origin = mViewPager.getPaddingStart();
             int leftBoundary = -view.getWidth();
             int rightBoundary = mViewPager.getWidth();
             int pageWidth = view.getWidth();
             int offset = (int) (pageWidth * position);

             //               left      origin     right
             //             boundary              boundary
             // ---------------|----------|----------|----------
             // Cover alpha:  1.0         0         1.0
             float alpha;
             if (offset <= leftBoundary || offset >= rightBoundary) {
                 alpha = 1.0f;
             } else if (offset <= origin) {
                 // offset in (leftBoundary, origin]
                 alpha = (float) Math.abs(offset - origin) / Math.abs(leftBoundary - origin);
             } else {
                 // offset in (origin, rightBoundary)
                 alpha = (float) Math.abs(offset - origin) / Math.abs(rightBoundary - origin);
             }
             View cover = view.findViewById(R.id.fade_cover);
             if (cover != null) {
                 view.findViewById(R.id.fade_cover).setAlpha(alpha);
             }
         }, LAYER_TYPE_NONE);
         mViewPager.setPageMargin(res.getDimensionPixelOffset(R.dimen.preview_page_gap));
         mViewPager.setClipToPadding(false);
         if (mPageStyle == STYLE_PEEKING) {
             int screenWidth = mViewPager.getResources().getDisplayMetrics().widthPixels;
             int hMargin = res.getDimensionPixelOffset(R.dimen.preview_page_horizontal_margin);
             hMargin = Math.max(hMargin, screenWidth/8);
             mViewPager.setPadding(
                     hMargin,
                     res.getDimensionPixelOffset(R.dimen.preview_page_top_margin),
                     hMargin,
                     res.getDimensionPixelOffset(R.dimen.preview_page_bottom_margin));
         } else if (mPageStyle == STYLE_ASPECT_RATIO) {
             WindowManager windowManager = context.getSystemService(WindowManager.class);
             Point screenSize = ScreenSizeCalculator.getInstance()
                     .getScreenSize(windowManager.getDefaultDisplay());
             mScreenAspectRatio = (float) screenSize.y / screenSize.x;
             mViewPager.setPadding(
                     0,
                     res.getDimensionPixelOffset(R.dimen.preview_page_top_margin),
                     0,
                     res.getDimensionPixelOffset(R.dimen.preview_page_bottom_margin));
             // Set the default margin to make sure not peeking the second page before calculating
             // the real margin.
             mViewPager.setPageMargin(screenSize.x / 2);
             mViewPager.addOnLayoutChangeListener(new OnLayoutChangeListener() {
                 @Override
                 public void onLayoutChange(View view, int left, int top, int right, int bottom,
                                            int oldLeft, int oldTop, int oldRight, int oldBottom) {
                     // Set the minimum margin which can't peek the second page.
                     mViewPager.setPageMargin(view.getPaddingEnd());
                     mViewPager.removeOnLayoutChangeListener(this);
                 }
             });
         }
         setupPagerScroller(context);
         mPageIndicator = findViewById(R.id.page_indicator);
         mPreviousArrow = findViewById(R.id.arrow_previous);
         mPreviousArrow.setOnClickListener(v -> {
             final int previousPos = mViewPager.getCurrentItem() - 1;
             mViewPager.setCurrentItem(previousPos, true);
         });
         mNextArrow = findViewById(R.id.arrow_next);
         mNextArrow.setOnClickListener(v -> {
             final int NextPos = mViewPager.getCurrentItem() + 1;
             mViewPager.setCurrentItem(NextPos, true);
         });
         mPageListener = createPageListener();
         mViewPager.addOnPageChangeListener(mPageListener);
     }

     @Override
     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
         View parentView = (View) getParent();
         float parentHeight = parentView != null ? parentView.getMeasuredHeight() : 0;
         if (parentHeight > 0) {
             int maxHeight = Math.min(MeasureSpec.getSize(heightMeasureSpec),
                     (int) (parentHeight * mMaxHeightRatio));
             heightMeasureSpec = MeasureSpec.makeMeasureSpec(maxHeight, MeasureSpec.AT_MOST);
         }

         if (mPageStyle == STYLE_ASPECT_RATIO) {
             int availableWidth = MeasureSpec.getSize(widthMeasureSpec);
             int availableHeight = MeasureSpec.getSize(heightMeasureSpec);
             int indicatorHeight = ((View) mPageIndicator.getParent()).getLayoutParams().height;
             int pagerHeight = availableHeight - indicatorHeight;
             if (availableWidth > 0) {
                 int absoluteCardWidth = (int) ((pagerHeight - mViewPager.getPaddingBottom()
                         - mViewPager.getPaddingTop())/ mScreenAspectRatio);
                 int hPadding = (availableWidth / 2) - (absoluteCardWidth / 2);
                 mViewPager.setPaddingRelative(
                         hPadding,
                         mViewPager.getPaddingTop(),
                         hPadding,
                         mViewPager.getPaddingBottom());
             }
         }

         super.onMeasure(widthMeasureSpec, heightMeasureSpec);
     }

     public void forceCardWidth(int widthPixels) {
         mViewPager.addOnLayoutChangeListener(new OnLayoutChangeListener() {
             @Override
             public void onLayoutChange(View v, int left, int top, int right, int bottom,
                     int oldLeft, int oldTop, int oldRight, int oldBottom) {
                 int hPadding = (mViewPager.getWidth() - widthPixels) / 2;
                 mViewPager.setPadding(hPadding, mViewPager.getPaddingTop(),
                         hPadding, mViewPager.getPaddingBottom());
                 mViewPager.removeOnLayoutChangeListener(this);
             }
         });
         mViewPager.invalidate();
     }

     /**
      * Call this method to set the {@link PagerAdapter} backing the {@link ViewPager} in this
      * widget.
      */
     public void setAdapter(@Nullable PagerAdapter adapter) {
         if (adapter == null) {
             mAdapter = null;
             mViewPager.setAdapter(null);
             return;
         }
         int initialPage = 0;
         if (mViewPager.getAdapter() != null) {
             initialPage = isRtl() ? mAdapter.getCount() - 1 - mViewPager.getCurrentItem()
                     : mViewPager.getCurrentItem();
         }
         mAdapter = adapter;
         mViewPager.setAdapter(adapter);
         mViewPager.setCurrentItem(isRtl() ? mAdapter.getCount() - 1 - initialPage : initialPage);
         mAdapter.registerDataSetObserver(new DataSetObserver() {
             @Override
             public void onChanged() {
                 initIndicator();
             }
         });
         initIndicator();
         updateIndicator(mViewPager.getCurrentItem());
     }

     /**
      * Checks if it is in RTL mode.
      *
      * @return {@code true} if it's in RTL mode; {@code false} otherwise.
      */
     public boolean isRtl() {
         if (ViewCompat.isLayoutDirectionResolved(mViewPager)) {
             return ViewCompat.getLayoutDirection(mViewPager) == ViewCompat.LAYOUT_DIRECTION_RTL;
         }
         return TextUtilsCompat.getLayoutDirectionFromLocale(Locale.getDefault())
                 == ViewCompat.LAYOUT_DIRECTION_RTL;
     }

     /**
      * Set a {@link OnPageChangeListener} to be notified when the ViewPager's page state changes
      */
     public void setOnPageChangeListener(@Nullable ViewPager.OnPageChangeListener listener) {
         mExternalPageListener = listener;
     }

     /**
      * Switches to the specific preview page.
      *
      * @param index preview page index to select
      */
     public void switchPreviewPage(int index) {
         mViewPager.setCurrentItem(index);
     }

     private void initIndicator() {
         mPageIndicator.setNumPages(mAdapter.getCount());
         mPageIndicator.setLocation(mViewPager.getCurrentItem());
     }

     private void setupPagerScroller(Context context) {
         try {
             // TODO(b/159082165): Revisit if we can refactor it better.
             Field scroller = ViewPager.class.getDeclaredField("mScroller");
             scroller.setAccessible(true);
             PreviewPagerScroller previewPagerScroller =
                     new PreviewPagerScroller(context, new LinearOutSlowInInterpolator());
             scroller.set(mViewPager, previewPagerScroller);
         } catch (NoSuchFieldException | IllegalArgumentException | IllegalAccessException e) {
             Log.e(TAG, "Failed to setup pager scroller.", e);
         }
     }

     private ViewPager.OnPageChangeListener createPageListener() {
         return new ViewPager.OnPageChangeListener() {
              @Override
              public void onPageScrolled(
                      int position, float positionOffset, int positionOffsetPixels) {
                  // For certain sizes, positionOffset never makes it to 1, so round it as we don't
                  // need that much precision
                  float location = (float) Math.round((position + positionOffset) * 100) / 100;
                  mPageIndicator.setLocation(location);
                  if (mExternalPageListener != null) {
                      mExternalPageListener.onPageScrolled(position, positionOffset,
                              positionOffsetPixels);
                  }
              }

              @Override
              public void onPageSelected(int position) {
                  int adapterCount = mAdapter.getCount();
                  if (position < 0 || position >= adapterCount) {
                      return;
                  }

                  updateIndicator(position);
                  if (mExternalPageListener != null) {
                      mExternalPageListener.onPageSelected(position);
                  }
              }

              @Override
              public void onPageScrollStateChanged(int state) {
                  if (mExternalPageListener != null) {
                      mExternalPageListener.onPageScrollStateChanged(state);
                  }
              }
         };
     }

     private void updateIndicator(int position) {
         int adapterCount = mAdapter.getCount();
         if (adapterCount > 1) {
             mPreviousArrow.setVisibility(position != 0 ? View.VISIBLE : View.GONE);
             mNextArrow.setVisibility(position != (adapterCount - 1) ? View.VISIBLE : View.GONE);
         } else {
             mPageIndicator.setVisibility(View.GONE);
             mPreviousArrow.setVisibility(View.GONE);
             mNextArrow.setVisibility(View.GONE);
         }
     }

     private static class PreviewPagerScroller extends Scroller {

         private static final int DURATION_MS = 500;

         PreviewPagerScroller(Context context, Interpolator interpolator) {
             super(context, interpolator);
         }

         @Override
         public void startScroll(int startX, int startY, int dx, int dy, int duration) {
             super.startScroll(startX, startY, dx, dy, DURATION_MS);
         }
     }
 }
	/*
	* Copyright (C) 2018 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.wallpaper.widget;

	import android.content.Context;
	import android.content.res.Resources;
	import android.content.res.TypedArray;
	import android.database.DataSetObserver;
	import android.graphics.Point;
	import android.util.AttributeSet;
	import android.util.Log;
	import android.util.TypedValue;
	import android.view.LayoutInflater;
	import android.view.View;
	import android.view.WindowManager;
	import android.view.animation.Interpolator;
	import android.widget.LinearLayout;
	import android.widget.Scroller;

	import androidx.annotation.Nullable;
	import androidx.core.text.TextUtilsCompat;
	import androidx.core.view.ViewCompat;
	import androidx.interpolator.view.animation.LinearOutSlowInInterpolator;
	import androidx.viewpager.widget.PagerAdapter;
	import androidx.viewpager.widget.ViewPager;
	import androidx.viewpager.widget.ViewPager.OnPageChangeListener;

	import com.android.wallpaper.R;
	import com.android.wallpaper.util.ScreenSizeCalculator;

	import java.lang.reflect.Field;
	import java.util.Locale;

	/**
	* A Widget consisting of a ViewPager linked to a PageIndicator and previous/next arrows that can be
	* used to page over that ViewPager.
	* To use it, set a {@link PagerAdapter} using {@link #setAdapter(PagerAdapter)}, and optionally use
	* a {@link #setOnPageChangeListener(OnPageChangeListener)} to listen for page changes.
	*/
	public class PreviewPager extends LinearLayout {

	private static final String TAG = "PreviewPager";
	private static final int STYLE_PEEKING = 0;
	private static final int STYLE_ASPECT_RATIO = 1;

	private final ViewPager mViewPager;
	private final PageIndicator mPageIndicator;
	private final View mPreviousArrow;
	private final View mNextArrow;
	private final ViewPager.OnPageChangeListener mPageListener;
	private int mPageStyle;

	private PagerAdapter mAdapter;
	private ViewPager.OnPageChangeListener mExternalPageListener;
	private float mScreenAspectRatio;
	/** The maximum height ratio of PreviewPager and its parent view. */
	private float mMaxHeightRatio;

	public PreviewPager(Context context) {
	this(context, null);
	}

	public PreviewPager(Context context, AttributeSet attrs) {
	this(context, attrs, 0);
	}

	public PreviewPager(Context context, AttributeSet attrs, int defStyleAttr) {
	super(context, attrs, defStyleAttr);
	LayoutInflater.from(context).inflate(R.layout.preview_pager, this);
	Resources res = context.getResources();
	TypedArray a = context.obtainStyledAttributes(attrs,
	R.styleable.PreviewPager, defStyleAttr, 0);

	mPageStyle = a.getInteger(R.styleable.PreviewPager_card_style, STYLE_PEEKING);

	a.recycle();

	TypedValue ratioValue = new TypedValue();
	res.getValue(R.dimen.preview_pager_maximum_height_ratio, ratioValue, true);
	mMaxHeightRatio = ratioValue.getFloat();

	mViewPager = findViewById(R.id.preview_viewpager);
	mViewPager.setPageTransformer(false, (view, position) -> {
	int origin = mViewPager.getPaddingStart();
	int leftBoundary = -view.getWidth();
	int rightBoundary = mViewPager.getWidth();
	int pageWidth = view.getWidth();
	int offset = (int) (pageWidth * position);

	// left origin right
	// boundary boundary
	// ---------------\|----------\|----------\|----------
	// Cover alpha: 1.0 0 1.0
	float alpha;
	if (offset <= leftBoundary \|\| offset >= rightBoundary) {
	alpha = 1.0f;
	} else if (offset <= origin) {
	// offset in (leftBoundary, origin]
	alpha = (float) Math.abs(offset - origin) / Math.abs(leftBoundary - origin);
	} else {
	// offset in (origin, rightBoundary)
	alpha = (float) Math.abs(offset - origin) / Math.abs(rightBoundary - origin);
	}
	View cover = view.findViewById(R.id.fade_cover);
	if (cover != null) {
	view.findViewById(R.id.fade_cover).setAlpha(alpha);
	}
	}, LAYER_TYPE_NONE);
	mViewPager.setPageMargin(res.getDimensionPixelOffset(R.dimen.preview_page_gap));
	mViewPager.setClipToPadding(false);
	if (mPageStyle == STYLE_PEEKING) {
	int screenWidth = mViewPager.getResources().getDisplayMetrics().widthPixels;
	int hMargin = res.getDimensionPixelOffset(R.dimen.preview_page_horizontal_margin);
	hMargin = Math.max(hMargin, screenWidth/8);
	mViewPager.setPadding(
	hMargin,
	res.getDimensionPixelOffset(R.dimen.preview_page_top_margin),
	hMargin,
	res.getDimensionPixelOffset(R.dimen.preview_page_bottom_margin));
	} else if (mPageStyle == STYLE_ASPECT_RATIO) {
	WindowManager windowManager = context.getSystemService(WindowManager.class);
	Point screenSize = ScreenSizeCalculator.getInstance()
	.getScreenSize(windowManager.getDefaultDisplay());
	mScreenAspectRatio = (float) screenSize.y / screenSize.x;
	mViewPager.setPadding(
	0,
	res.getDimensionPixelOffset(R.dimen.preview_page_top_margin),
	0,
	res.getDimensionPixelOffset(R.dimen.preview_page_bottom_margin));
	// Set the default margin to make sure not peeking the second page before calculating
	// the real margin.
	mViewPager.setPageMargin(screenSize.x / 2);
	mViewPager.addOnLayoutChangeListener(new OnLayoutChangeListener() {
	@Override
	public void onLayoutChange(View view, int left, int top, int right, int bottom,
	int oldLeft, int oldTop, int oldRight, int oldBottom) {
	// Set the minimum margin which can't peek the second page.
	mViewPager.setPageMargin(view.getPaddingEnd());
	mViewPager.removeOnLayoutChangeListener(this);
	}
	});
	}
	setupPagerScroller(context);
	mPageIndicator = findViewById(R.id.page_indicator);
	mPreviousArrow = findViewById(R.id.arrow_previous);
	mPreviousArrow.setOnClickListener(v -> {
	final int previousPos = mViewPager.getCurrentItem() - 1;
	mViewPager.setCurrentItem(previousPos, true);
	});
	mNextArrow = findViewById(R.id.arrow_next);
	mNextArrow.setOnClickListener(v -> {
	final int NextPos = mViewPager.getCurrentItem() + 1;
	mViewPager.setCurrentItem(NextPos, true);
	});
	mPageListener = createPageListener();
	mViewPager.addOnPageChangeListener(mPageListener);
	}

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
	View parentView = (View) getParent();
	float parentHeight = parentView != null ? parentView.getMeasuredHeight() : 0;
	if (parentHeight > 0) {
	int maxHeight = Math.min(MeasureSpec.getSize(heightMeasureSpec),
	(int) (parentHeight * mMaxHeightRatio));
	heightMeasureSpec = MeasureSpec.makeMeasureSpec(maxHeight, MeasureSpec.AT_MOST);
	}

	if (mPageStyle == STYLE_ASPECT_RATIO) {
	int availableWidth = MeasureSpec.getSize(widthMeasureSpec);
	int availableHeight = MeasureSpec.getSize(heightMeasureSpec);
	int indicatorHeight = ((View) mPageIndicator.getParent()).getLayoutParams().height;
	int pagerHeight = availableHeight - indicatorHeight;
	if (availableWidth > 0) {
	int absoluteCardWidth = (int) ((pagerHeight - mViewPager.getPaddingBottom()
	- mViewPager.getPaddingTop())/ mScreenAspectRatio);
	int hPadding = (availableWidth / 2) - (absoluteCardWidth / 2);
	mViewPager.setPaddingRelative(
	hPadding,
	mViewPager.getPaddingTop(),
	hPadding,
	mViewPager.getPaddingBottom());
	}
	}

	super.onMeasure(widthMeasureSpec, heightMeasureSpec);
	}

	public void forceCardWidth(int widthPixels) {
	mViewPager.addOnLayoutChangeListener(new OnLayoutChangeListener() {
	@Override
	public void onLayoutChange(View v, int left, int top, int right, int bottom,
	int oldLeft, int oldTop, int oldRight, int oldBottom) {
	int hPadding = (mViewPager.getWidth() - widthPixels) / 2;
	mViewPager.setPadding(hPadding, mViewPager.getPaddingTop(),
	hPadding, mViewPager.getPaddingBottom());
	mViewPager.removeOnLayoutChangeListener(this);
	}
	});
	mViewPager.invalidate();
	}

	/**
	* Call this method to set the {@link PagerAdapter} backing the {@link ViewPager} in this
	* widget.
	*/
	public void setAdapter(@Nullable PagerAdapter adapter) {
	if (adapter == null) {
	mAdapter = null;
	mViewPager.setAdapter(null);
	return;
	}
	int initialPage = 0;
	if (mViewPager.getAdapter() != null) {
	initialPage = isRtl() ? mAdapter.getCount() - 1 - mViewPager.getCurrentItem()
	: mViewPager.getCurrentItem();
	}
	mAdapter = adapter;
	mViewPager.setAdapter(adapter);
	mViewPager.setCurrentItem(isRtl() ? mAdapter.getCount() - 1 - initialPage : initialPage);
	mAdapter.registerDataSetObserver(new DataSetObserver() {
	@Override
	public void onChanged() {
	initIndicator();
	}
	});
	initIndicator();
	updateIndicator(mViewPager.getCurrentItem());
	}

	/**
	* Checks if it is in RTL mode.
	*
	* @return {@code true} if it's in RTL mode; {@code false} otherwise.
	*/
	public boolean isRtl() {
	if (ViewCompat.isLayoutDirectionResolved(mViewPager)) {
	return ViewCompat.getLayoutDirection(mViewPager) == ViewCompat.LAYOUT_DIRECTION_RTL;
	}
	return TextUtilsCompat.getLayoutDirectionFromLocale(Locale.getDefault())
	== ViewCompat.LAYOUT_DIRECTION_RTL;
	}

	/**
	* Set a {@link OnPageChangeListener} to be notified when the ViewPager's page state changes
	*/
	public void setOnPageChangeListener(@Nullable ViewPager.OnPageChangeListener listener) {
	mExternalPageListener = listener;
	}

	/**
	* Switches to the specific preview page.
	*
	* @param index preview page index to select
	*/
	public void switchPreviewPage(int index) {
	mViewPager.setCurrentItem(index);
	}

	private void initIndicator() {
	mPageIndicator.setNumPages(mAdapter.getCount());
	mPageIndicator.setLocation(mViewPager.getCurrentItem());
	}

	private void setupPagerScroller(Context context) {
	try {
	// TODO(b/159082165): Revisit if we can refactor it better.
	Field scroller = ViewPager.class.getDeclaredField("mScroller");
	scroller.setAccessible(true);
	PreviewPagerScroller previewPagerScroller =
	new PreviewPagerScroller(context, new LinearOutSlowInInterpolator());
	scroller.set(mViewPager, previewPagerScroller);
	} catch (NoSuchFieldException \| IllegalArgumentException \| IllegalAccessException e) {
	Log.e(TAG, "Failed to setup pager scroller.", e);
	}
	}

	private ViewPager.OnPageChangeListener createPageListener() {
	return new ViewPager.OnPageChangeListener() {
	@Override
	public void onPageScrolled(
	int position, float positionOffset, int positionOffsetPixels) {
	// For certain sizes, positionOffset never makes it to 1, so round it as we don't
	// need that much precision
	float location = (float) Math.round((position + positionOffset) * 100) / 100;
	mPageIndicator.setLocation(location);
	if (mExternalPageListener != null) {
	mExternalPageListener.onPageScrolled(position, positionOffset,
	positionOffsetPixels);
	}
	}

	@Override
	public void onPageSelected(int position) {
	int adapterCount = mAdapter.getCount();
	if (position < 0 \|\| position >= adapterCount) {
	return;
	}

	updateIndicator(position);
	if (mExternalPageListener != null) {
	mExternalPageListener.onPageSelected(position);
	}
	}

	@Override
	public void onPageScrollStateChanged(int state) {
	if (mExternalPageListener != null) {
	mExternalPageListener.onPageScrollStateChanged(state);
	}
	}
	};
	}

	private void updateIndicator(int position) {
	int adapterCount = mAdapter.getCount();
	if (adapterCount > 1) {
	mPreviousArrow.setVisibility(position != 0 ? View.VISIBLE : View.GONE);
	mNextArrow.setVisibility(position != (adapterCount - 1) ? View.VISIBLE : View.GONE);
	} else {
	mPageIndicator.setVisibility(View.GONE);
	mPreviousArrow.setVisibility(View.GONE);
	mNextArrow.setVisibility(View.GONE);
	}
	}

	private static class PreviewPagerScroller extends Scroller {

	private static final int DURATION_MS = 500;

	PreviewPagerScroller(Context context, Interpolator interpolator) {
	super(context, interpolator);
	}

	@Override
	public void startScroll(int startX, int startY, int dx, int dy, int duration) {
	super.startScroll(startX, startY, dx, dy, DURATION_MS);
	}
	}
	}