src/com/android/providers/media/photopicker/ui/PreviewFragment.java - platform/packages/providers/MediaProvider - Git at Google

 /*
  * Copyright (C) 2021 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.providers.media.photopicker.ui;

 import android.content.Context;
 import android.content.res.Configuration;
 import android.graphics.Color;
 import android.os.Bundle;
 import android.text.TextUtils;
 import android.util.Log;
 import android.view.LayoutInflater;
 import android.view.Menu;
 import android.view.MenuInflater;
 import android.view.MenuItem;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.Button;

 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentManager;
 import androidx.lifecycle.ViewModelProvider;
 import androidx.viewpager2.widget.ViewPager2;

 import com.android.providers.media.R;
 import com.android.providers.media.photopicker.PhotoPickerActivity;
 import com.android.providers.media.photopicker.data.MuteStatus;
 import com.android.providers.media.photopicker.data.Selection;
 import com.android.providers.media.photopicker.data.model.Item;
 import com.android.providers.media.photopicker.util.LayoutModeUtils;
 import com.android.providers.media.photopicker.viewmodel.PickerViewModel;

 import java.text.NumberFormat;
 import java.util.List;
 import java.util.Locale;

 /**
  * Displays a selected items in one up view. Supports deselecting items.
  */
 public class PreviewFragment extends Fragment {
     private static String TAG = "PreviewFragment";

     private static final String PREVIEW_TYPE = "preview_type";
     private static final int PREVIEW_ON_LONG_PRESS = 1;
     private static final int PREVIEW_ON_VIEW_SELECTED = 2;

     private static final Bundle sPreviewOnLongPressArgs = new Bundle();
     static {
         sPreviewOnLongPressArgs.putInt(PREVIEW_TYPE, PREVIEW_ON_LONG_PRESS);
     }
     private static final Bundle sPreviewOnViewSelectedArgs = new Bundle();
     static {
         sPreviewOnViewSelectedArgs.putInt(PREVIEW_TYPE, PREVIEW_ON_VIEW_SELECTED);
     }

     private Selection mSelection;
     private PickerViewModel mPickerViewModel;
     private ViewPager2Wrapper mViewPager2Wrapper;
     private boolean mShouldShowGifBadge;
     private boolean mShouldShowMotionPhotoBadge;
     private MuteStatus mMuteStatus;

     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         // Register with the activity to inform the system that the app bar fragment is
         // participating in the population of the options menu
         setHasOptionsMenu(true);
     }

     @Override
     public void onCreateOptionsMenu(@NonNull Menu menu, @NonNull MenuInflater inflater) {
         inflater.inflate(R.menu.picker_preview_menu, menu);
     }

     @Override
     public void onPrepareOptionsMenu(@NonNull Menu menu) {
         super.onPrepareOptionsMenu(menu);
         // All logic to hide/show an item in the menu must be in this method
         final MenuItem gifItem = menu.findItem(R.id.preview_gif);
         final MenuItem motionPhotoItem = menu.findItem(R.id.preview_motion_photo);
         gifItem.setVisible(mShouldShowGifBadge);
         motionPhotoItem.setVisible(mShouldShowMotionPhotoBadge);
     }

     @Override
     public View onCreateView(LayoutInflater inflater, ViewGroup parent,
             Bundle savedInstanceState) {
         mPickerViewModel = new ViewModelProvider(requireActivity()).get(PickerViewModel.class);
         mSelection = mPickerViewModel.getSelection();
         mMuteStatus = mPickerViewModel.getMuteStatus();
         return inflater.inflate(R.layout.fragment_preview, parent, /* attachToRoot */ false);
     }

     @Override
     public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
         // Set the pane title for A11y.
         view.setAccessibilityPaneTitle(getString(R.string.picker_preview));
         final List<Item> selectedItemsList = mSelection.getSelectedItemsForPreview();
         final int selectedItemsListSize = selectedItemsList.size();

         if (selectedItemsListSize <= 0) {
             // This can happen if we lost PickerViewModel to optimize memory.
             Log.e(TAG, "No items to preview. Returning back to photo grid");
             requireActivity().getSupportFragmentManager().popBackStack();
         } else if (selectedItemsListSize > 1 && !mSelection.canSelectMultiple()) {
             // This should never happen
             throw new IllegalStateException("Found more than one preview items in single select"
                     + " mode. Selected items count: " + selectedItemsListSize);
         }

         // Initialize ViewPager2 to swipe between multiple pictures/videos in preview
         final ViewPager2 viewPager = view.findViewById(R.id.preview_viewPager);
         if (viewPager == null) {
             throw new IllegalStateException("Expected to find ViewPager2 in " + view
                     + ", but found null");
         }
         mViewPager2Wrapper = new ViewPager2Wrapper(viewPager, selectedItemsList, mMuteStatus);

         setUpPreviewLayout(view, getArguments());
         setupScrimLayerAndBottomBar(view);
     }

     private void setupScrimLayerAndBottomBar(View fragmentView) {
         final boolean isLandscape = getResources().getConfiguration().orientation
                 == Configuration.ORIENTATION_LANDSCAPE;

         // Show the scrim layers in Landscape mode. The default visibility is GONE.
         if (isLandscape) {
             final View topScrim = fragmentView.findViewById(R.id.preview_top_scrim);
             topScrim.setVisibility(View.VISIBLE);

             final View bottomScrim = fragmentView.findViewById(R.id.preview_bottom_scrim);
             bottomScrim.setVisibility(View.VISIBLE);
         }

         // Set appropriate background color for the bottom bar
         final int bottomBarColor;
         if (isLandscape) {
             bottomBarColor = Color.TRANSPARENT;
         } else {
             bottomBarColor = getContext().getColor(R.color.preview_scrim_solid_color);
         }
         final View bottomBar = fragmentView.findViewById(R.id.preview_bottom_bar);
         bottomBar.setBackgroundColor(bottomBarColor);
     }

     private void setUpPreviewLayout(@NonNull View view, @Nullable Bundle args) {
         if (args == null) {
             // We are willing to crash PhotoPickerActivity because this error might only happen
             // during development.
             throw new IllegalArgumentException("Can't determine the type of the Preview, arguments"
                     + " is not set");
         }

         final int previewType = args.getInt(PREVIEW_TYPE, -1);
         if (previewType == PREVIEW_ON_LONG_PRESS) {
             setUpPreviewLayoutForLongPress(view);
         } else if (previewType == PREVIEW_ON_VIEW_SELECTED) {
             setUpPreviewLayoutForViewSelected(view);
         } else {
             // We are willing to crash PhotoPickerActivity because this error might only happen
             // during development.
             throw new IllegalArgumentException("No preview type specified");
         }
     }

     /**
      * Adjusts the select/add button layout for preview on LongPress
      */
     private void setUpPreviewLayoutForLongPress(@NonNull View view) {
         final Button addOrSelectButton = view.findViewById(R.id.preview_add_or_select_button);

         // Preview on Long Press will reuse AddOrSelect button as
         // * Add button - Button with text "Add" - for single select mode
         // * Select button - Button with text "Select"/"Deselect" based on the selection state of
         //                   the item - for multi select mode
         if (!mSelection.canSelectMultiple()) {
             // On clicking add button we return the picker result to calling app.
             // This destroys PickerActivity and all fragments.
             addOrSelectButton.setOnClickListener(v -> {
                 ((PhotoPickerActivity) getActivity()).setResultAndFinishSelf();
             });
         } else {
             // For preview on long press, we always preview only one item.
             // Selection#getSelectedItemsForPreview is guaranteed to return only one item. Hence,
             // we can always use position=0 as current position.
             updateSelectButtonText(addOrSelectButton,
                     mSelection.isItemSelected(mViewPager2Wrapper.getItemAt(/* position */ 0)));
             addOrSelectButton.setOnClickListener(v -> onClickSelectButton(addOrSelectButton));
         }

         // Set the appropriate special format icon based on the item in the preview
         updateSpecialFormatIcon(mViewPager2Wrapper.getItemAt(/* position */ 0));
     }

     /**
      * Adjusts the layout based on Multi select and adds appropriate onClick listeners
      */
     private void setUpPreviewLayoutForViewSelected(@NonNull View view) {
         // Hide addOrSelect button of long press, we have a separate add button for view selected
         final Button addOrSelectButton = view.findViewById(R.id.preview_add_or_select_button);
         addOrSelectButton.setVisibility(View.GONE);

         final Button viewSelectedAddButton = view.findViewById(R.id.preview_add_button);
         viewSelectedAddButton.setVisibility(View.VISIBLE);
         // On clicking add button we return the picker result to calling app.
         // This destroys PickerActivity and all fragments.
         viewSelectedAddButton.setOnClickListener(v -> {
             ((PhotoPickerActivity) getActivity()).setResultAndFinishSelf();
         });

         final Button selectedCheckButton = view.findViewById(R.id.preview_selected_check_button);
         selectedCheckButton.setVisibility(View.VISIBLE);
         // Update the select icon and text according to the state of selection while swiping
         // between photos
         mViewPager2Wrapper.addOnPageChangeCallback(new OnPageChangeCallback(selectedCheckButton));

         // Update add button text to include number of items selected.
         mSelection
                 .getSelectedItemCount()
                 .observe(
                         this,
                         selectedItemCount -> {
                             viewSelectedAddButton.setText(
                                     generateAddButtonString(
                                             /* context= */ getContext(),
                                             /* size= */ selectedItemCount,
                                             /* isUserSelectForApp= */ mPickerViewModel
                                                     .isUserSelectForApp()));
                         });

         selectedCheckButton.setOnClickListener(
                 v -> onClickSelectedCheckButton(selectedCheckButton));
     }

     @Override
     public void onResume() {
         super.onResume();

         ((PhotoPickerActivity) getActivity()).updateCommonLayouts(LayoutModeUtils.MODE_PREVIEW,
                 /* title */"");
     }

     @Override
     public void onStop() {
         super.onStop();

         if (mViewPager2Wrapper != null) {
             mViewPager2Wrapper.onStop();
         }
     }

     @Override
     public void onStart() {
         super.onStart();

         if (mViewPager2Wrapper != null) {
             mViewPager2Wrapper.onStart();
         }
     }

     @Override
     public void onDestroy() {
         super.onDestroy();
         if (mViewPager2Wrapper != null) {
             mViewPager2Wrapper.onDestroy();
         }
     }

     private void onClickSelectButton(@NonNull Button selectButton) {
         final boolean isSelectedNow = updateSelectionAndGetState();
         updateSelectButtonText(selectButton, isSelectedNow);
     }

     private void onClickSelectedCheckButton(@NonNull Button selectedCheckButton) {
         final boolean isSelectedNow = updateSelectionAndGetState();
         updateSelectedCheckButtonStateAndText(selectedCheckButton, isSelectedNow);
     }

     private boolean updateSelectionAndGetState() {
         final Item currentItem = mViewPager2Wrapper.getCurrentItem();
         final boolean wasSelectedBefore = mSelection.isItemSelected(currentItem);

         if (wasSelectedBefore) {
             // If the item is previously selected, current user action is to deselect the item
             mSelection.removeSelectedItem(currentItem);
         } else {
             // If the item is not previously selected, current user action is to select the item
             mSelection.addSelectedItem(currentItem);
         }

         // After the user has clicked the button, current state of the button should be opposite of
         // the previous state.
         // If the previous state was to "Select" the item, and user clicks "Select" button,
         // wasSelectedBefore = false. And item will be added to selected items. Now, user can only
         // deselect the item. Hence, isSelectedNow is opposite of previous state,
         // i.e., isSelectedNow = true.
         return !wasSelectedBefore;
     }

     private class OnPageChangeCallback extends ViewPager2.OnPageChangeCallback {
         private final Button mSelectedCheckButton;

         public OnPageChangeCallback(@NonNull Button selectedCheckButton) {
             mSelectedCheckButton = selectedCheckButton;
         }

         @Override
         public void onPageSelected(int position) {
             // No action to take as we don't have deselect view here.
             if (!mSelection.canSelectMultiple()) return;

             final Item item = mViewPager2Wrapper.getItemAt(position);
             // Set the appropriate select/deselect state for each item in each page based on the
             // selection list.
             updateSelectedCheckButtonStateAndText(mSelectedCheckButton,
                     mSelection.isItemSelected(item));

             // Set the appropriate special format icon based on the item in the preview
             updateSpecialFormatIcon(item);
         }
     }

     private static void updateSelectButtonText(@NonNull Button selectButton,
             boolean isSelected) {
         selectButton.setText(isSelected ? R.string.deselect : R.string.select);
     }

     private static void updateSelectedCheckButtonStateAndText(@NonNull Button selectedCheckButton,
             boolean isSelected) {
         selectedCheckButton.setText(isSelected ? R.string.selected : R.string.deselected);
         selectedCheckButton.setSelected(isSelected);
     }

     private void updateSpecialFormatIcon(Item item) {
         mShouldShowGifBadge = item.isGifOrAnimatedWebp();
         mShouldShowMotionPhotoBadge = item.isMotionPhoto();
         // Invalidating options menu calls onPrepareOptionsMenu() where the logic for
         // hiding/showing menu items is placed.
         requireActivity().invalidateOptionsMenu();
     }

     public static void show(@NonNull FragmentManager fm, @NonNull Bundle args) {
         if (fm.isStateSaved()) {
             Log.d(TAG, "Skip show preview fragment because state saved");
             return;
         }

         final PreviewFragment fragment = new PreviewFragment();
         fragment.setArguments(args);
         fm.beginTransaction()
                 .replace(R.id.fragment_container, fragment, TAG)
                 .addToBackStack(TAG)
                 .commitAllowingStateLoss();
     }

     /**
      * Get the fragment in the FragmentManager
      * @param fm the fragment manager
      */
     public static Fragment get(@NonNull FragmentManager fm) {
         return fm.findFragmentByTag(TAG);
     }

     public static Bundle getArgsForPreviewOnLongPress() {
         return sPreviewOnLongPressArgs;
     }

     public static Bundle getArgsForPreviewOnViewSelected() {
         return sPreviewOnViewSelectedArgs;
     }

     // TODO: There is a same method in TabFragment. To find a way to reuse it.
     private static String generateAddButtonString(
             @NonNull Context context, int size, boolean isUserSelectForApp) {
         final String sizeString = NumberFormat.getInstance(Locale.getDefault()).format(size);
         final String template =
                 isUserSelectForApp
                         ? context.getString(R.string.picker_add_button_multi_select_permissions)
                         : context.getString(R.string.picker_add_button_multi_select);
         return TextUtils.expandTemplate(template, sizeString).toString();
     }
 }
	/*
	* Copyright (C) 2021 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.providers.media.photopicker.ui;

	import android.content.Context;
	import android.content.res.Configuration;
	import android.graphics.Color;
	import android.os.Bundle;
	import android.text.TextUtils;
	import android.util.Log;
	import android.view.LayoutInflater;
	import android.view.Menu;
	import android.view.MenuInflater;
	import android.view.MenuItem;
	import android.view.View;
	import android.view.ViewGroup;
	import android.widget.Button;

	import androidx.annotation.NonNull;
	import androidx.annotation.Nullable;
	import androidx.fragment.app.Fragment;
	import androidx.fragment.app.FragmentManager;
	import androidx.lifecycle.ViewModelProvider;
	import androidx.viewpager2.widget.ViewPager2;

	import com.android.providers.media.R;
	import com.android.providers.media.photopicker.PhotoPickerActivity;
	import com.android.providers.media.photopicker.data.MuteStatus;
	import com.android.providers.media.photopicker.data.Selection;
	import com.android.providers.media.photopicker.data.model.Item;
	import com.android.providers.media.photopicker.util.LayoutModeUtils;
	import com.android.providers.media.photopicker.viewmodel.PickerViewModel;

	import java.text.NumberFormat;
	import java.util.List;
	import java.util.Locale;

	/**
	* Displays a selected items in one up view. Supports deselecting items.
	*/
	public class PreviewFragment extends Fragment {
	private static String TAG = "PreviewFragment";

	private static final String PREVIEW_TYPE = "preview_type";
	private static final int PREVIEW_ON_LONG_PRESS = 1;
	private static final int PREVIEW_ON_VIEW_SELECTED = 2;

	private static final Bundle sPreviewOnLongPressArgs = new Bundle();
	static {
	sPreviewOnLongPressArgs.putInt(PREVIEW_TYPE, PREVIEW_ON_LONG_PRESS);
	}
	private static final Bundle sPreviewOnViewSelectedArgs = new Bundle();
	static {
	sPreviewOnViewSelectedArgs.putInt(PREVIEW_TYPE, PREVIEW_ON_VIEW_SELECTED);
	}

	private Selection mSelection;
	private PickerViewModel mPickerViewModel;
	private ViewPager2Wrapper mViewPager2Wrapper;
	private boolean mShouldShowGifBadge;
	private boolean mShouldShowMotionPhotoBadge;
	private MuteStatus mMuteStatus;

	@Override
	public void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	// Register with the activity to inform the system that the app bar fragment is
	// participating in the population of the options menu
	setHasOptionsMenu(true);
	}

	@Override
	public void onCreateOptionsMenu(@NonNull Menu menu, @NonNull MenuInflater inflater) {
	inflater.inflate(R.menu.picker_preview_menu, menu);
	}

	@Override
	public void onPrepareOptionsMenu(@NonNull Menu menu) {
	super.onPrepareOptionsMenu(menu);
	// All logic to hide/show an item in the menu must be in this method
	final MenuItem gifItem = menu.findItem(R.id.preview_gif);
	final MenuItem motionPhotoItem = menu.findItem(R.id.preview_motion_photo);
	gifItem.setVisible(mShouldShowGifBadge);
	motionPhotoItem.setVisible(mShouldShowMotionPhotoBadge);
	}

	@Override
	public View onCreateView(LayoutInflater inflater, ViewGroup parent,
	Bundle savedInstanceState) {
	mPickerViewModel = new ViewModelProvider(requireActivity()).get(PickerViewModel.class);
	mSelection = mPickerViewModel.getSelection();
	mMuteStatus = mPickerViewModel.getMuteStatus();
	return inflater.inflate(R.layout.fragment_preview, parent, /* attachToRoot */ false);
	}

	@Override
	public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
	// Set the pane title for A11y.
	view.setAccessibilityPaneTitle(getString(R.string.picker_preview));
	final List<Item> selectedItemsList = mSelection.getSelectedItemsForPreview();
	final int selectedItemsListSize = selectedItemsList.size();

	if (selectedItemsListSize <= 0) {
	// This can happen if we lost PickerViewModel to optimize memory.
	Log.e(TAG, "No items to preview. Returning back to photo grid");
	requireActivity().getSupportFragmentManager().popBackStack();
	} else if (selectedItemsListSize > 1 && !mSelection.canSelectMultiple()) {
	// This should never happen
	throw new IllegalStateException("Found more than one preview items in single select"
	+ " mode. Selected items count: " + selectedItemsListSize);
	}

	// Initialize ViewPager2 to swipe between multiple pictures/videos in preview
	final ViewPager2 viewPager = view.findViewById(R.id.preview_viewPager);
	if (viewPager == null) {
	throw new IllegalStateException("Expected to find ViewPager2 in " + view
	+ ", but found null");
	}
	mViewPager2Wrapper = new ViewPager2Wrapper(viewPager, selectedItemsList, mMuteStatus);

	setUpPreviewLayout(view, getArguments());
	setupScrimLayerAndBottomBar(view);
	}

	private void setupScrimLayerAndBottomBar(View fragmentView) {
	final boolean isLandscape = getResources().getConfiguration().orientation
	== Configuration.ORIENTATION_LANDSCAPE;

	// Show the scrim layers in Landscape mode. The default visibility is GONE.
	if (isLandscape) {
	final View topScrim = fragmentView.findViewById(R.id.preview_top_scrim);
	topScrim.setVisibility(View.VISIBLE);

	final View bottomScrim = fragmentView.findViewById(R.id.preview_bottom_scrim);
	bottomScrim.setVisibility(View.VISIBLE);
	}

	// Set appropriate background color for the bottom bar
	final int bottomBarColor;
	if (isLandscape) {
	bottomBarColor = Color.TRANSPARENT;
	} else {
	bottomBarColor = getContext().getColor(R.color.preview_scrim_solid_color);
	}
	final View bottomBar = fragmentView.findViewById(R.id.preview_bottom_bar);
	bottomBar.setBackgroundColor(bottomBarColor);
	}

	private void setUpPreviewLayout(@NonNull View view, @Nullable Bundle args) {
	if (args == null) {
	// We are willing to crash PhotoPickerActivity because this error might only happen
	// during development.
	throw new IllegalArgumentException("Can't determine the type of the Preview, arguments"
	+ " is not set");
	}

	final int previewType = args.getInt(PREVIEW_TYPE, -1);
	if (previewType == PREVIEW_ON_LONG_PRESS) {
	setUpPreviewLayoutForLongPress(view);
	} else if (previewType == PREVIEW_ON_VIEW_SELECTED) {
	setUpPreviewLayoutForViewSelected(view);
	} else {
	// We are willing to crash PhotoPickerActivity because this error might only happen
	// during development.
	throw new IllegalArgumentException("No preview type specified");
	}
	}

	/**
	* Adjusts the select/add button layout for preview on LongPress
	*/
	private void setUpPreviewLayoutForLongPress(@NonNull View view) {
	final Button addOrSelectButton = view.findViewById(R.id.preview_add_or_select_button);

	// Preview on Long Press will reuse AddOrSelect button as
	// * Add button - Button with text "Add" - for single select mode
	// * Select button - Button with text "Select"/"Deselect" based on the selection state of
	// the item - for multi select mode
	if (!mSelection.canSelectMultiple()) {
	// On clicking add button we return the picker result to calling app.
	// This destroys PickerActivity and all fragments.
	addOrSelectButton.setOnClickListener(v -> {
	((PhotoPickerActivity) getActivity()).setResultAndFinishSelf();
	});
	} else {
	// For preview on long press, we always preview only one item.
	// Selection#getSelectedItemsForPreview is guaranteed to return only one item. Hence,
	// we can always use position=0 as current position.
	updateSelectButtonText(addOrSelectButton,
	mSelection.isItemSelected(mViewPager2Wrapper.getItemAt(/* position */ 0)));
	addOrSelectButton.setOnClickListener(v -> onClickSelectButton(addOrSelectButton));
	}

	// Set the appropriate special format icon based on the item in the preview
	updateSpecialFormatIcon(mViewPager2Wrapper.getItemAt(/* position */ 0));
	}

	/**
	* Adjusts the layout based on Multi select and adds appropriate onClick listeners
	*/
	private void setUpPreviewLayoutForViewSelected(@NonNull View view) {
	// Hide addOrSelect button of long press, we have a separate add button for view selected
	final Button addOrSelectButton = view.findViewById(R.id.preview_add_or_select_button);
	addOrSelectButton.setVisibility(View.GONE);

	final Button viewSelectedAddButton = view.findViewById(R.id.preview_add_button);
	viewSelectedAddButton.setVisibility(View.VISIBLE);
	// On clicking add button we return the picker result to calling app.
	// This destroys PickerActivity and all fragments.
	viewSelectedAddButton.setOnClickListener(v -> {
	((PhotoPickerActivity) getActivity()).setResultAndFinishSelf();
	});

	final Button selectedCheckButton = view.findViewById(R.id.preview_selected_check_button);
	selectedCheckButton.setVisibility(View.VISIBLE);
	// Update the select icon and text according to the state of selection while swiping
	// between photos
	mViewPager2Wrapper.addOnPageChangeCallback(new OnPageChangeCallback(selectedCheckButton));

	// Update add button text to include number of items selected.
	mSelection
	.getSelectedItemCount()
	.observe(
	this,
	selectedItemCount -> {
	viewSelectedAddButton.setText(
	generateAddButtonString(
	/* context= */ getContext(),
	/* size= */ selectedItemCount,
	/* isUserSelectForApp= */ mPickerViewModel
	.isUserSelectForApp()));
	});

	selectedCheckButton.setOnClickListener(
	v -> onClickSelectedCheckButton(selectedCheckButton));
	}

	@Override
	public void onResume() {
	super.onResume();

	((PhotoPickerActivity) getActivity()).updateCommonLayouts(LayoutModeUtils.MODE_PREVIEW,
	/* title */"");
	}

	@Override
	public void onStop() {
	super.onStop();

	if (mViewPager2Wrapper != null) {
	mViewPager2Wrapper.onStop();
	}
	}

	@Override
	public void onStart() {
	super.onStart();

	if (mViewPager2Wrapper != null) {
	mViewPager2Wrapper.onStart();
	}
	}

	@Override
	public void onDestroy() {
	super.onDestroy();
	if (mViewPager2Wrapper != null) {
	mViewPager2Wrapper.onDestroy();
	}
	}

	private void onClickSelectButton(@NonNull Button selectButton) {
	final boolean isSelectedNow = updateSelectionAndGetState();
	updateSelectButtonText(selectButton, isSelectedNow);
	}

	private void onClickSelectedCheckButton(@NonNull Button selectedCheckButton) {
	final boolean isSelectedNow = updateSelectionAndGetState();
	updateSelectedCheckButtonStateAndText(selectedCheckButton, isSelectedNow);
	}

	private boolean updateSelectionAndGetState() {
	final Item currentItem = mViewPager2Wrapper.getCurrentItem();
	final boolean wasSelectedBefore = mSelection.isItemSelected(currentItem);

	if (wasSelectedBefore) {
	// If the item is previously selected, current user action is to deselect the item
	mSelection.removeSelectedItem(currentItem);
	} else {
	// If the item is not previously selected, current user action is to select the item
	mSelection.addSelectedItem(currentItem);
	}

	// After the user has clicked the button, current state of the button should be opposite of
	// the previous state.
	// If the previous state was to "Select" the item, and user clicks "Select" button,
	// wasSelectedBefore = false. And item will be added to selected items. Now, user can only
	// deselect the item. Hence, isSelectedNow is opposite of previous state,
	// i.e., isSelectedNow = true.
	return !wasSelectedBefore;
	}

	private class OnPageChangeCallback extends ViewPager2.OnPageChangeCallback {
	private final Button mSelectedCheckButton;

	public OnPageChangeCallback(@NonNull Button selectedCheckButton) {
	mSelectedCheckButton = selectedCheckButton;
	}

	@Override
	public void onPageSelected(int position) {
	// No action to take as we don't have deselect view here.
	if (!mSelection.canSelectMultiple()) return;

	final Item item = mViewPager2Wrapper.getItemAt(position);
	// Set the appropriate select/deselect state for each item in each page based on the
	// selection list.
	updateSelectedCheckButtonStateAndText(mSelectedCheckButton,
	mSelection.isItemSelected(item));

	// Set the appropriate special format icon based on the item in the preview
	updateSpecialFormatIcon(item);
	}
	}

	private static void updateSelectButtonText(@NonNull Button selectButton,
	boolean isSelected) {
	selectButton.setText(isSelected ? R.string.deselect : R.string.select);
	}

	private static void updateSelectedCheckButtonStateAndText(@NonNull Button selectedCheckButton,
	boolean isSelected) {
	selectedCheckButton.setText(isSelected ? R.string.selected : R.string.deselected);
	selectedCheckButton.setSelected(isSelected);
	}

	private void updateSpecialFormatIcon(Item item) {
	mShouldShowGifBadge = item.isGifOrAnimatedWebp();
	mShouldShowMotionPhotoBadge = item.isMotionPhoto();
	// Invalidating options menu calls onPrepareOptionsMenu() where the logic for
	// hiding/showing menu items is placed.
	requireActivity().invalidateOptionsMenu();
	}

	public static void show(@NonNull FragmentManager fm, @NonNull Bundle args) {
	if (fm.isStateSaved()) {
	Log.d(TAG, "Skip show preview fragment because state saved");
	return;
	}

	final PreviewFragment fragment = new PreviewFragment();
	fragment.setArguments(args);
	fm.beginTransaction()
	.replace(R.id.fragment_container, fragment, TAG)
	.addToBackStack(TAG)
	.commitAllowingStateLoss();
	}

	/**
	* Get the fragment in the FragmentManager
	* @param fm the fragment manager
	*/
	public static Fragment get(@NonNull FragmentManager fm) {
	return fm.findFragmentByTag(TAG);
	}

	public static Bundle getArgsForPreviewOnLongPress() {
	return sPreviewOnLongPressArgs;
	}

	public static Bundle getArgsForPreviewOnViewSelected() {
	return sPreviewOnViewSelectedArgs;
	}

	// TODO: There is a same method in TabFragment. To find a way to reuse it.
	private static String generateAddButtonString(
	@NonNull Context context, int size, boolean isUserSelectForApp) {
	final String sizeString = NumberFormat.getInstance(Locale.getDefault()).format(size);
	final String template =
	isUserSelectForApp
	? context.getString(R.string.picker_add_button_multi_select_permissions)
	: context.getString(R.string.picker_add_button_multi_select);
	return TextUtils.expandTemplate(template, sizeString).toString();
	}
	}