Migrate to ViewPager2 (#1544)

* migrate MainActivty to ViewPager2

* migrate AccountActivty to ViewPager2

* migrate ViewMediaActivty to ViewPager2

* migrate SearchActivity to ViewPager2

* checkin missing AccountPagerAdapter file

* remove unused class ImageViewPager

* replace SparseArray with MutableList

app/build.gradle

@@ -114,6 +114,7 @@ dependencies {
     implementation 'androidx.cardview:cardview:1.0.0'
     implementation 'androidx.preference:preference:1.1.0'
     implementation 'androidx.sharetarget:sharetarget:1.0.0-beta01'
+    implementation "androidx.viewpager2:viewpager2:1.0.0-rc01"
     implementation "com.squareup.retrofit2:retrofit:$retrofitVersion"
     implementation "com.squareup.retrofit2:converter-gson:$retrofitVersion"
     implementation "com.squareup.retrofit2:adapter-rxjava2:$retrofitVersion"

app/src/main/java/com/keylesspalace/tusky/AccountActivity.kt

@@ -37,6 +37,7 @@ import androidx.lifecycle.Observer
 import androidx.lifecycle.ViewModelProviders
 import androidx.preference.PreferenceManager
 import androidx.recyclerview.widget.LinearLayoutManager
+import androidx.viewpager2.widget.MarginPageTransformer
 import com.bumptech.glide.Glide
 import com.google.android.material.appbar.AppBarLayout
 import com.google.android.material.appbar.CollapsingToolbarLayout
@@ -45,6 +46,7 @@ import com.google.android.material.shape.MaterialShapeDrawable
 import com.google.android.material.shape.ShapeAppearanceModel
 import com.google.android.material.snackbar.Snackbar
 import com.google.android.material.tabs.TabLayout
+import com.google.android.material.tabs.TabLayoutMediator
 import com.keylesspalace.tusky.adapter.AccountFieldAdapter
 import com.keylesspalace.tusky.components.report.ReportActivity
 import com.keylesspalace.tusky.di.ViewModelFactory
@@ -187,16 +189,21 @@ class AccountActivity : BottomSheetActivity(), ActionButtonActivity, HasAndroidI
      */
     private fun setupTabs() {
         // Setup the tabs and timeline pager.
-        adapter = AccountPagerAdapter(supportFragmentManager, viewModel.accountId)
+        adapter = AccountPagerAdapter(this, viewModel.accountId)
-        val pageTitles = arrayOf(getString(R.string.title_statuses), getString(R.string.title_statuses_with_replies), getString(R.string.title_statuses_pinned), getString(R.string.title_media))
+
-        adapter.setPageTitles(pageTitles)
-        accountFragmentViewPager.pageMargin = resources.getDimensionPixelSize(R.dimen.tab_page_margin)
-        val pageMarginDrawable = ThemeUtils.getDrawable(this, R.attr.tab_page_margin_drawable,
-                R.drawable.tab_page_margin_dark)
-        accountFragmentViewPager.setPageMarginDrawable(pageMarginDrawable)
         accountFragmentViewPager.adapter = adapter
         accountFragmentViewPager.offscreenPageLimit = 2
-        accountTabLayout.setupWithViewPager(accountFragmentViewPager)
+
+        val pageTitles = arrayOf(getString(R.string.title_statuses), getString(R.string.title_statuses_with_replies), getString(R.string.title_statuses_pinned), getString(R.string.title_media))
+
+        TabLayoutMediator(accountTabLayout, accountFragmentViewPager) {
+            tab, position ->
+            tab.text = pageTitles[position]
+        }.attach()
+
+        val pageMargin = resources.getDimensionPixelSize(R.dimen.tab_page_margin)
+        accountFragmentViewPager.setPageTransformer(MarginPageTransformer(pageMargin))
+
         accountTabLayout.addOnTabSelectedListener(object : TabLayout.OnTabSelectedListener {
             override fun onTabReselected(tab: TabLayout.Tab?) {
                 tab?.position?.let { position ->

app/src/main/java/com/keylesspalace/tusky/MainActivity.java

@@ -33,11 +33,13 @@ import androidx.emoji.text.EmojiCompat;
 import androidx.fragment.app.Fragment;
 import androidx.lifecycle.Lifecycle;
 import androidx.preference.PreferenceManager;
-import androidx.viewpager.widget.ViewPager;
+import androidx.viewpager2.widget.MarginPageTransformer;
+import androidx.viewpager2.widget.ViewPager2;
 
 import com.bumptech.glide.Glide;
 import com.google.android.material.floatingactionbutton.FloatingActionButton;
 import com.google.android.material.tabs.TabLayout;
+import com.google.android.material.tabs.TabLayoutMediator;
 import com.keylesspalace.tusky.appstore.CacheUpdater;
 import com.keylesspalace.tusky.appstore.EventHub;
 import com.keylesspalace.tusky.appstore.MainTabsChangedEvent;
@@ -53,7 +55,6 @@ import com.keylesspalace.tusky.pager.MainPagerAdapter;
 import com.keylesspalace.tusky.util.CustomEmojiHelper;
 import com.keylesspalace.tusky.util.NotificationHelper;
 import com.keylesspalace.tusky.util.ShareShortcutHelper;
-import com.keylesspalace.tusky.util.ThemeUtils;
 import com.mikepenz.google_material_typeface_library.GoogleMaterial;
 import com.mikepenz.materialdrawer.AccountHeader;
 import com.mikepenz.materialdrawer.AccountHeaderBuilder;
@@ -114,7 +115,7 @@ public final class MainActivity extends BottomSheetActivity implements ActionBut
     private AccountHeader headerResult;
     private Drawer drawer;
     private TabLayout tabLayout;
-    private ViewPager viewPager;
+    private ViewPager2 viewPager;
 
     private int notificationTabPosition;
     private MainPagerAdapter adapter;
@@ -207,10 +208,7 @@ public final class MainActivity extends BottomSheetActivity implements ActionBut
         setupTabs(showNotificationTab);
 
         int pageMargin = getResources().getDimensionPixelSize(R.dimen.tab_page_margin);
-        viewPager.setPageMargin(pageMargin);
+        viewPager.setPageTransformer(new MarginPageTransformer(pageMargin));
-        Drawable pageMarginDrawable = ThemeUtils.getDrawable(this, R.attr.tab_page_margin_drawable,
-                R.drawable.tab_page_margin_dark);
-        viewPager.setPageMarginDrawable(pageMarginDrawable);
 
         tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
             @Override
@@ -467,10 +465,11 @@ public final class MainActivity extends BottomSheetActivity implements ActionBut
     private void setupTabs(boolean selectNotificationTab) {
         List<TabData> tabs = accountManager.getActiveAccount().getTabPreferences();
 
-        adapter = new MainPagerAdapter(tabs, getSupportFragmentManager());
+        adapter = new MainPagerAdapter(tabs, this);
         viewPager.setAdapter(adapter);
 
-        tabLayout.setupWithViewPager(viewPager);
+        new TabLayoutMediator(tabLayout, viewPager, (tab, position) -> { }).attach();
+
         tabLayout.removeAllTabs();
         for (int i = 0; i < tabs.size(); i++) {
             TabLayout.Tab tab = tabLayout.newTab()

app/src/main/java/com/keylesspalace/tusky/ViewMediaActivity.kt

@@ -37,9 +37,10 @@ import android.view.View
 import android.webkit.MimeTypeMap
 import android.widget.Toast
 import androidx.core.content.FileProvider
+import androidx.fragment.app.FragmentActivity
 import androidx.lifecycle.Lifecycle
-import androidx.viewpager.widget.PagerAdapter
+import androidx.viewpager2.adapter.FragmentStateAdapter
-import androidx.viewpager.widget.ViewPager
+import androidx.viewpager2.widget.ViewPager2
 import com.bumptech.glide.Glide
 import com.bumptech.glide.request.FutureTarget
 import com.keylesspalace.tusky.BuildConfig.APPLICATION_ID
@@ -110,23 +111,23 @@ class ViewMediaActivity : BaseActivity(), ViewImageFragment.PhotoActionsListener
         // Adapter is actually of existential type PageAdapter & SharedElementsTransitionListener
         // but it cannot be expressed and if I don't specify type explicitly compilation fails
         // (probably a bug in compiler)
-        val adapter: PagerAdapter = if (attachments != null) {
+        val adapter: ViewMediaAdapter = if (attachments != null) {
             val realAttachs = attachments!!.map(AttachmentViewData::attachment)
             // Setup the view pager.
-            ImagePagerAdapter(supportFragmentManager, realAttachs, initialPosition)
+            ImagePagerAdapter(this, realAttachs, initialPosition)
 
         } else {
             val avatarUrl = intent.getStringExtra(EXTRA_AVATAR_URL)
                     ?: throw IllegalArgumentException("attachment list or avatar url has to be set")
 
-            AvatarImagePagerAdapter(supportFragmentManager, avatarUrl)
+            AvatarImagePagerAdapter(this, avatarUrl)
         }
 
         viewPager.adapter = adapter
-        viewPager.currentItem = initialPosition
+        viewPager.setCurrentItem(initialPosition, false)
-        viewPager.addOnPageChangeListener(object : ViewPager.SimpleOnPageChangeListener() {
+        viewPager.registerOnPageChangeCallback(object: ViewPager2.OnPageChangeCallback() {
             override fun onPageSelected(position: Int) {
-                toolbar.title = adapter.getPageTitle(position)
+                toolbar.title = getPageTitle(position)
             }
         })
 
@@ -136,7 +137,7 @@ class ViewMediaActivity : BaseActivity(), ViewImageFragment.PhotoActionsListener
         if (actionBar != null) {
             actionBar.setDisplayHomeAsUpEnabled(true)
             actionBar.setDisplayShowHomeEnabled(true)
-            actionBar.title = adapter.getPageTitle(initialPosition)
+            actionBar.title = getPageTitle(initialPosition)
         }
         toolbar.setNavigationOnClickListener { supportFinishAfterTransition() }
         toolbar.setOnMenuItemClickListener { item: MenuItem ->
@@ -153,7 +154,7 @@ class ViewMediaActivity : BaseActivity(), ViewImageFragment.PhotoActionsListener
         window.statusBarColor = Color.BLACK
         window.sharedElementEnterTransition.addListener(object : NoopTransitionListener {
             override fun onTransitionEnd(transition: Transition) {
-                (adapter as SharedElementTransitionListener).onTransitionEnd()
+                adapter.onTransitionEnd(viewPager.currentItem)
                 window.sharedElementEnterTransition.removeListener(this)
             }
         })
@@ -198,6 +199,13 @@ class ViewMediaActivity : BaseActivity(), ViewImageFragment.PhotoActionsListener
                 .start()
     }
 
+    private fun getPageTitle(position: Int): CharSequence {
+        if(attachments == null) {
+            return ""
+        }
+        return String.format(Locale.getDefault(), "%d/%d", position + 1, attachments?.size)
+    }
+
     private fun downloadMedia() {
         val url = attachments!![viewPager.currentItem].attachment.url
         val filename = Uri.parse(url).lastPathSegment
@@ -323,8 +331,8 @@ class ViewMediaActivity : BaseActivity(), ViewImageFragment.PhotoActionsListener
     }
 }
 
-interface SharedElementTransitionListener {
+abstract class ViewMediaAdapter(activity: FragmentActivity): FragmentStateAdapter(activity) {
-    fun onTransitionEnd()
+    abstract fun onTransitionEnd(position: Int)
 }
 
 interface NoopTransitionListener : Transition.TransitionListener {

app/src/main/java/com/keylesspalace/tusky/components/search/SearchActivity.kt

@@ -23,6 +23,7 @@ import android.view.Menu
 import android.view.MenuItem
 import androidx.appcompat.widget.SearchView
 import androidx.lifecycle.ViewModelProviders
+import com.google.android.material.tabs.TabLayoutMediator
 import com.keylesspalace.tusky.BottomSheetActivity
 import com.keylesspalace.tusky.R
 import com.keylesspalace.tusky.components.search.adapter.SearchPagerAdapter
@@ -57,8 +58,12 @@ class SearchActivity : BottomSheetActivity(), SearchView.OnQueryTextListener, Ha
     }
 
     private fun setupPages() {
-        pages.adapter = SearchPagerAdapter(this, supportFragmentManager)
+        pages.adapter = SearchPagerAdapter(this)
-        tabs.setupWithViewPager(pages)
+
+        TabLayoutMediator(tabs, pages) {
+            tab, position ->
+            tab.text = getPageTitle(position)
+        }.attach()
     }
 
     override fun onNewIntent(intent: Intent) {
@@ -99,6 +104,15 @@ class SearchActivity : BottomSheetActivity(), SearchView.OnQueryTextListener, Ha
         return false
     }
 
+    private fun getPageTitle(position: Int): CharSequence? {
+        return when (position) {
+            0 -> getString(R.string.title_statuses)
+            1 -> getString(R.string.title_accounts)
+            2 -> getString(R.string.title_hashtags_dialog)
+            else -> throw IllegalArgumentException("Unknown page index: $position")
+        }
+    }
+
     private fun handleIntent(intent: Intent) {
         if (Intent.ACTION_SEARCH == intent.action) {
             viewModel.currentQuery = intent.getStringExtra(SearchManager.QUERY)

app/src/main/java/com/keylesspalace/tusky/components/search/adapter/SearchPagerAdapter.kt

@@ -15,18 +15,16 @@
 
 package com.keylesspalace.tusky.components.search.adapter
 
-import android.content.Context
 import androidx.fragment.app.Fragment
-import androidx.fragment.app.FragmentManager
+import androidx.fragment.app.FragmentActivity
-import androidx.fragment.app.FragmentPagerAdapter
+import androidx.viewpager2.adapter.FragmentStateAdapter
-import com.keylesspalace.tusky.R
-import com.keylesspalace.tusky.components.search.SearchType
 import com.keylesspalace.tusky.components.search.fragments.SearchAccountsFragment
 import com.keylesspalace.tusky.components.search.fragments.SearchHashtagsFragment
 import com.keylesspalace.tusky.components.search.fragments.SearchStatusesFragment
 
-class SearchPagerAdapter(private val context: Context, manager: FragmentManager) : FragmentPagerAdapter(manager) {
+class SearchPagerAdapter(activity: FragmentActivity) : FragmentStateAdapter(activity) {
-    override fun getItem(position: Int): Fragment {
+
+    override fun createFragment(position: Int): Fragment {
         return when (position) {
             0 -> SearchStatusesFragment.newInstance()
             1 -> SearchAccountsFragment.newInstance()
@@ -35,14 +33,6 @@ class SearchPagerAdapter(private val context: Context, manager: FragmentManager)
         }
     }
 
-    override fun getPageTitle(position: Int): CharSequence? {
+    override fun getItemCount() = 3
-        return when (position) {
-            0 -> context.getString(R.string.title_statuses)
-            1 -> context.getString(R.string.title_accounts)
-            2 -> context.getString(R.string.title_hashtags_dialog)
-            else -> throw IllegalArgumentException("Unknown page index: $position")
-        }
-    }
 
-    override fun getCount(): Int = 3
 }

app/src/main/java/com/keylesspalace/tusky/fragment/AccountMediaFragment.kt

@@ -81,7 +81,6 @@ class AccountMediaFragment : BaseFragment(), RefreshableFragment, Injectable {
     private var currentCall: Call<List<Status>>? = null
     private val statuses = mutableListOf<Status>()
     private var fetchingStatus = FetchingStatus.NOT_FETCHING
-    private var isVisibleToUser: Boolean = false
 
     private lateinit var accountId: String
 
@@ -216,7 +215,7 @@ class AccountMediaFragment : BaseFragment(), RefreshableFragment, Injectable {
             }
         })
 
-        if (isVisibleToUser) doInitialLoadingIfNeeded()
+        doInitialLoadingIfNeeded()
     }
 
     private fun refresh() {
@@ -235,14 +234,6 @@ class AccountMediaFragment : BaseFragment(), RefreshableFragment, Injectable {
             topProgressBar?.show()
     }
 
-    // That's sort of an optimization to only load media once user has opened the tab
-    // Attention: can be called before *any* lifecycle method!
-    override fun setUserVisibleHint(isVisibleToUser: Boolean) {
-        super.setUserVisibleHint(isVisibleToUser)
-        this.isVisibleToUser = isVisibleToUser
-        if (isVisibleToUser && isAdded) doInitialLoadingIfNeeded()
-    }
-
     private fun doInitialLoadingIfNeeded() {
         if (isAdded) {
             statusView.hide()

app/src/main/java/com/keylesspalace/tusky/fragment/ViewMediaFragment.kt

@@ -18,13 +18,12 @@ package com.keylesspalace.tusky.fragment
 import android.os.Bundle
 import android.text.TextUtils
 import android.widget.TextView
-import com.keylesspalace.tusky.SharedElementTransitionListener
 
 import com.keylesspalace.tusky.ViewMediaActivity
 import com.keylesspalace.tusky.entity.Attachment
 import com.keylesspalace.tusky.util.visible
 
-abstract class ViewMediaFragment : BaseFragment(), SharedElementTransitionListener {
+abstract class ViewMediaFragment : BaseFragment() {
     private var toolbarVisibiltyDisposable: Function0<Boolean>? = null
 
     abstract fun setupMediaView(url: String, previewUrl: String?)
@@ -71,6 +70,8 @@ abstract class ViewMediaFragment : BaseFragment(), SharedElementTransitionListen
         }
     }
 
+    abstract fun onTransitionEnd()
+
     protected fun finalizeViewSetup(url: String, previewUrl: String?, description: String?) {
         val mediaActivity = activity as ViewMediaActivity
         setupMediaView(url, previewUrl)

app/src/main/java/com/keylesspalace/tusky/pager/AccountPagerAdapter.java

@@ -1,120 +0,0 @@
-/* Copyright 2017 Andrew Dawson
- *
- * This file is a part of Tusky.
- *
- * This program is free software; you can redistribute it and/or modify it under the terms of the
- * GNU General Public License as published by the Free Software Foundation; either version 3 of the
- * License, or (at your option) any later version.
- *
- * Tusky is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
- * the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
- * Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with Tusky; if not,
- * see <http://www.gnu.org/licenses>. */
-
-package com.keylesspalace.tusky.pager;
-
-import android.util.SparseArray;
-import android.view.ViewGroup;
-
-import com.keylesspalace.tusky.fragment.AccountMediaFragment;
-import com.keylesspalace.tusky.fragment.TimelineFragment;
-import com.keylesspalace.tusky.interfaces.RefreshableFragment;
-
-import java.util.HashSet;
-import java.util.Set;
-
-import androidx.annotation.NonNull;
-import androidx.annotation.Nullable;
-import androidx.fragment.app.Fragment;
-import androidx.fragment.app.FragmentManager;
-import androidx.fragment.app.FragmentPagerAdapter;
-
-public class AccountPagerAdapter extends FragmentPagerAdapter {
-    private static final int TAB_COUNT = 4;
-    private String accountId;
-    private String[] pageTitles;
-
-    private SparseArray<Fragment> fragments = new SparseArray<>(TAB_COUNT);
-
-    private final Set<Integer> pagesToRefresh = new HashSet<>();
-
-    public AccountPagerAdapter(FragmentManager manager, String accountId) {
-        super(manager);
-        this.accountId = accountId;
-    }
-
-    public void setPageTitles(String[] titles) {
-        pageTitles = titles;
-    }
-
-    @NonNull
-    @Override
-    public Fragment getItem(int position) {
-        switch (position) {
-            case 0: {
-                return TimelineFragment.newInstance(TimelineFragment.Kind.USER, accountId,false);
-            }
-            case 1: {
-                return TimelineFragment.newInstance(TimelineFragment.Kind.USER_WITH_REPLIES, accountId,false);
-            }
-            case 2: {
-                return TimelineFragment.newInstance(TimelineFragment.Kind.USER_PINNED, accountId,false);
-            }
-            case 3: {
-                return AccountMediaFragment.newInstance(accountId,false);
-            }
-            default: {
-                throw new AssertionError("Page " + position + " is out of AccountPagerAdapter bounds");
-            }
-        }
-    }
-
-    @Override
-    public int getCount() {
-        return TAB_COUNT;
-    }
-
-    @NonNull
-    @Override
-    public Object instantiateItem(@NonNull ViewGroup container, int position) {
-        Object fragment = super.instantiateItem(container, position);
-        if (fragment instanceof Fragment)
-            fragments.put(position, (Fragment) fragment);
-        if (pagesToRefresh.contains(position)) {
-            if (fragment instanceof RefreshableFragment)
-                ((RefreshableFragment) fragment).refreshContent();
-            pagesToRefresh.remove(position);
-        }
-        return fragment;
-    }
-
-    @Override
-    public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
-        super.destroyItem(container, position, object);
-        fragments.remove(position);
-    }
-
-    @Override
-    public CharSequence getPageTitle(int position) {
-        return pageTitles[position];
-    }
-
-    @Nullable
-    public Fragment getFragment(int position) {
-        return fragments.get(position);
-    }
-
-    public void refreshContent(){
-        for (int i=0;i<getCount();i++){
-            Fragment fragment = getFragment(i);
-            if (fragment instanceof RefreshableFragment){
-                ((RefreshableFragment) fragment).refreshContent();
-            }
-            else{
-                pagesToRefresh.add(i);
-            }
-        }
-    }
-}

app/src/main/java/com/keylesspalace/tusky/pager/AccountPagerAdapter.kt

@@ -0,0 +1,65 @@
+/* Copyright 2019 Tusky Contributors
+ *
+ * This file is a part of Tusky.
+ *
+ * This program is free software; you can redistribute it and/or modify it under the terms of the
+ * GNU General Public License as published by the Free Software Foundation; either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * Tusky is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
+ * the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+ * Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with Tusky; if not,
+ * see <http://www.gnu.org/licenses>. */
+
+package com.keylesspalace.tusky.pager
+
+import androidx.fragment.app.*
+
+import com.keylesspalace.tusky.fragment.AccountMediaFragment
+import com.keylesspalace.tusky.fragment.TimelineFragment
+import com.keylesspalace.tusky.interfaces.RefreshableFragment
+
+import androidx.viewpager2.adapter.FragmentStateAdapter
+import java.lang.ref.WeakReference
+
+class AccountPagerAdapter(
+        activity: FragmentActivity,
+        private val accountId: String
+) : FragmentStateAdapter(activity) {
+
+    private val fragments = MutableList<WeakReference<Fragment>?>(TAB_COUNT) { null }
+
+    override fun getItemCount() = TAB_COUNT
+
+    override fun createFragment(position: Int): Fragment {
+        val fragment: Fragment = when (position) {
+            0 -> TimelineFragment.newInstance(TimelineFragment.Kind.USER, accountId, false)
+            1 -> TimelineFragment.newInstance(TimelineFragment.Kind.USER_WITH_REPLIES, accountId, false)
+            2 -> TimelineFragment.newInstance(TimelineFragment.Kind.USER_PINNED, accountId, false)
+            3 -> AccountMediaFragment.newInstance(accountId, false)
+            else -> throw AssertionError("Page $position is out of AccountPagerAdapter bounds")
+        }
+
+        fragments[position] = WeakReference(fragment)
+        return fragment
+    }
+
+    fun getFragment(position: Int): Fragment? {
+        return fragments[position]?.get()
+    }
+
+    fun refreshContent() {
+        for (i in 0 until TAB_COUNT) {
+            val fragment = getFragment(i)
+            if (fragment != null && fragment is RefreshableFragment) {
+                (fragment as RefreshableFragment).refreshContent()
+            }
+        }
+    }
+
+    companion object {
+        private const val TAB_COUNT = 4
+    }
+}

app/src/main/java/com/keylesspalace/tusky/pager/AvatarImagePagerAdapter.kt

@@ -1,13 +1,16 @@
 package com.keylesspalace.tusky.pager
 
 import androidx.fragment.app.Fragment
-import androidx.fragment.app.FragmentManager
+import androidx.fragment.app.FragmentActivity
-import androidx.fragment.app.FragmentPagerAdapter
+import com.keylesspalace.tusky.ViewMediaAdapter
-import com.keylesspalace.tusky.SharedElementTransitionListener
 import com.keylesspalace.tusky.fragment.ViewMediaFragment
 
-class AvatarImagePagerAdapter(fragmentManager: FragmentManager, private val avatarUrl: String) : FragmentPagerAdapter(fragmentManager), SharedElementTransitionListener {
+class AvatarImagePagerAdapter(
-    override fun getItem(position: Int): Fragment {
+        activity: FragmentActivity,
+        private val avatarUrl: String
+) : ViewMediaAdapter(activity) {
+
+    override fun createFragment(position: Int): Fragment {
         return if (position == 0) {
             ViewMediaFragment.newAvatarInstance(avatarUrl)
         } else {
@@ -15,8 +18,8 @@ class AvatarImagePagerAdapter(fragmentManager: FragmentManager, private val avat
         }
     }
 
-    override fun getCount() = 1
+    override fun getItemCount() = 1
 
-    override fun onTransitionEnd() {
+    override fun onTransitionEnd(position: Int) {
     }
 }

app/src/main/java/com/keylesspalace/tusky/pager/ImagePagerAdapter.kt

@@ -1,53 +1,42 @@
 package com.keylesspalace.tusky.pager
 
-import android.view.ViewGroup
 import androidx.fragment.app.Fragment
-import androidx.fragment.app.FragmentManager
+import androidx.fragment.app.FragmentActivity
-import androidx.fragment.app.FragmentStatePagerAdapter
+import com.keylesspalace.tusky.ViewMediaAdapter
-import com.keylesspalace.tusky.SharedElementTransitionListener
 import com.keylesspalace.tusky.entity.Attachment
 import com.keylesspalace.tusky.fragment.ViewMediaFragment
-import java.util.*
+import java.lang.ref.WeakReference
 
 class ImagePagerAdapter(
-        fragmentManager: FragmentManager,
+        activity: FragmentActivity,
         private val attachments: List<Attachment>,
         private val initialPosition: Int
-) : FragmentStatePagerAdapter(fragmentManager), SharedElementTransitionListener {
+) : ViewMediaAdapter(activity) {
 
-    private var primaryItem: ViewMediaFragment? = null
     private var didTransition = false
+    private val fragments = MutableList<WeakReference<ViewMediaFragment>?>(attachments.size) { null }
 
-    override fun setPrimaryItem(container: ViewGroup, position: Int, item: Any) {
+    override fun getItemCount() = attachments.size
-        super.setPrimaryItem(container, position, item)
-        this.primaryItem = item as ViewMediaFragment
-    }
 
-    override fun getItem(position: Int): Fragment {
+    override fun createFragment(position: Int): Fragment {
-        return if (position >= 0 && position < attachments.size) {
+        if (position >= 0 && position < attachments.size) {
             // Fragment should not wait for or start transition if it already happened but we
             // instantiate the same fragment again, e.g. open the first photo, scroll to the
-            // forth photo and then back to the first. The first fragment will trz to start the
+            // forth photo and then back to the first. The first fragment will try to start the
             // transition and wait until it's over and it will never take place.
-            ViewMediaFragment.newInstance(
+            val fragment = ViewMediaFragment.newInstance(
                     attachment = attachments[position],
                     shouldStartPostponedTransition = !didTransition && position == initialPosition
             )
+            fragments[position] = WeakReference(fragment)
+            return fragment
         } else {
             throw IllegalStateException()
         }
     }
 
-    override fun getCount(): Int {
+   override fun onTransitionEnd(position: Int) {
-        return attachments.size
-    }
-
-    override fun getPageTitle(position: Int): CharSequence {
-        return String.format(Locale.getDefault(), "%d/%d", position + 1, attachments.size)
-    }
-
-    override fun onTransitionEnd() {
         this.didTransition = true
-        primaryItem?.onTransitionEnd()
+        fragments[position]?.get()?.onTransitionEnd()
     }
 }

app/src/main/java/com/keylesspalace/tusky/pager/MainPagerAdapter.kt

@@ -15,49 +15,23 @@
 
 package com.keylesspalace.tusky.pager
 
-import android.util.SparseArray
-import android.view.ViewGroup
 import androidx.fragment.app.Fragment
-import androidx.fragment.app.FragmentManager
+import androidx.fragment.app.FragmentActivity
-import androidx.fragment.app.FragmentPagerAdapter
+import androidx.viewpager2.adapter.FragmentStateAdapter
-import androidx.viewpager.widget.PagerAdapter
 import com.keylesspalace.tusky.TabData
+import java.lang.ref.WeakReference
 
-class MainPagerAdapter(val tabs: List<TabData>, manager: FragmentManager) : FragmentPagerAdapter(manager) {
+class MainPagerAdapter(val tabs: List<TabData>, activity: FragmentActivity) : FragmentStateAdapter(activity) {
-    private val fragments = SparseArray<Fragment>(tabs.size)
+    private val fragments = MutableList<WeakReference<Fragment>?>(tabs.size) { null }
 
-    override fun getItem(position: Int): Fragment {
+    override fun createFragment(position: Int): Fragment {
         val tab = tabs[position]
-        return tab.fragment(tab.arguments)
+        val fragment = tab.fragment(tab.arguments)
-    }
+        fragments[position] = WeakReference(fragment)
-
-    override fun getCount(): Int {
-        return tabs.size
-    }
-
-    override fun getPageTitle(position: Int): CharSequence? {
-        return null
-    }
-
-    override fun getItemId(position: Int): Long {
-        return tabs[position].hashCode() + position.toLong()
-    }
-
-    override fun getItemPosition(item: Any): Int {
-        return PagerAdapter.POSITION_NONE
-    }
-
-    override fun instantiateItem(container: ViewGroup, position: Int): Any {
-        val fragment = super.instantiateItem(container, position)
-        if (fragment is Fragment)
-            fragments.put(position, fragment)
         return fragment
     }
 
-    override fun destroyItem(container: ViewGroup, position: Int, `object`: Any) {
+    override fun getItemCount() = tabs.size
-        super.destroyItem(container, position, `object`)
-        fragments.remove(position)
-    }
 
-    fun getFragment(position: Int): Fragment? = fragments[position]
+    fun getFragment(position: Int): Fragment? = fragments[position]?.get()
 }

app/src/main/java/com/keylesspalace/tusky/view/ImageViewPager.java

@@ -1,45 +0,0 @@
-/* Copyright 2017 Andrew Dawson
- *
- * This file is a part of Tusky.
- *
- * This program is free software; you can redistribute it and/or modify it under the terms of the
- * GNU General Public License as published by the Free Software Foundation; either version 3 of the
- * License, or (at your option) any later version.
- *
- * Tusky is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
- * the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
- * Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along with Tusky; if not,
- * see <http://www.gnu.org/licenses>. */
-
-package com.keylesspalace.tusky.view;
-
-import android.content.Context;
-import androidx.viewpager.widget.ViewPager;
-import android.util.AttributeSet;
-import android.view.MotionEvent;
-
-/**
- * This class is entirely to address a known issue with com.github.chrisbanes.photoview.PhotoView.
- * ViewPager will throw exceptions when a PhotoView is placed within it, so this subclass eats those
- * exceptions.
- */
-public class ImageViewPager extends ViewPager {
-    public ImageViewPager(Context context) {
-        super(context);
-    }
-
-    public ImageViewPager(Context context, AttributeSet attributeSet) {
-        super(context, attributeSet);
-    }
-
-    @Override
-    public boolean onInterceptTouchEvent(MotionEvent ev) {
-        try {
-            return super.onInterceptTouchEvent(ev);
-        } catch (IllegalArgumentException e) {
-            return false;
-        }
-    }
-}

app/src/main/res/drawable/tab_page_margin_black.xml

@@ -1,5 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<shape xmlns:android="http://schemas.android.com/apk/res/android"
-    android:shape="rectangle">
-    <solid android:color="@color/tab_page_margin_black" />
-</shape>

app/src/main/res/drawable/tab_page_margin_dark.xml

@@ -1,5 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<shape xmlns:android="http://schemas.android.com/apk/res/android"
-    android:shape="rectangle">
-    <solid android:color="@color/tab_page_margin_dark" />
-</shape>

app/src/main/res/drawable/tab_page_margin_light.xml

@@ -1,5 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<shape xmlns:android="http://schemas.android.com/apk/res/android"
-    android:shape="rectangle">
-    <solid android:color="@color/tab_page_margin_light" />
-</shape>

app/src/main/res/layout-sw640dp/fragment_timeline.xml

@@ -3,8 +3,7 @@
     xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
-    android:layout_height="match_parent"
+    android:layout_height="match_parent">
-    android:background="?attr/tab_page_margin_drawable">
 
     <androidx.constraintlayout.widget.ConstraintLayout
         android:layout_width="640dp"
@@ -45,16 +44,17 @@
             app:layout_constraintTop_toTopOf="parent"
             tools:src="@drawable/elephant_error"
             tools:visibility="visible" />
+
         <androidx.core.widget.ContentLoadingProgressBar
             android:id="@+id/topProgressBar"
+            style="@style/Widget.AppCompat.ProgressBar.Horizontal"
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
-            style="@style/Widget.AppCompat.ProgressBar.Horizontal"
-            app:layout_constraintTop_toTopOf="parent"
             android:indeterminate="true"
-            app:layout_constraintStart_toStartOf="parent"
+            android:visibility="gone"
-            app:layout_constraintEnd_toEndOf="parent"
             app:layout_constraintBottom_toTopOf="parent"
-            android:visibility="gone"/>
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toTopOf="parent" />
     </androidx.constraintlayout.widget.ConstraintLayout>
 </FrameLayout>

app/src/main/res/layout-sw640dp/fragment_timeline_notifications.xml

@@ -3,8 +3,7 @@
     xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
-    android:layout_height="match_parent"
+    android:layout_height="match_parent">
-    android:background="?attr/tab_page_margin_drawable">
 
     <androidx.coordinatorlayout.widget.CoordinatorLayout
         android:layout_width="640dp"
@@ -80,9 +79,7 @@
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_gravity="center"
-            android:src="@android:color/transparent"
             android:visibility="gone"
-            tools:src="@drawable/elephant_error"
             tools:visibility="visible" />
     </androidx.coordinatorlayout.widget.CoordinatorLayout>
 </FrameLayout>

app/src/main/res/layout-sw640dp/fragment_view_thread.xml

@@ -1,8 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
-    android:layout_height="match_parent"
+    android:layout_height="match_parent">
-    android:background="?attr/tab_page_margin_drawable">
 
     <androidx.swiperefreshlayout.widget.SwipeRefreshLayout
         android:id="@+id/swipeRefreshLayout"

app/src/main/res/layout/activity_account.xml

@@ -333,10 +333,11 @@
 
         </com.google.android.material.appbar.AppBarLayout>
 
-        <androidx.viewpager.widget.ViewPager
+        <androidx.viewpager2.widget.ViewPager2
             android:id="@+id/accountFragmentViewPager"
             android:layout_width="match_parent"
             android:layout_height="match_parent"
+            android:background="?attr/tab_page_margin_color"
             app:layout_behavior="@string/appbar_scrolling_view_behavior" />
 
         <com.google.android.material.floatingactionbutton.FloatingActionButton

app/src/main/res/layout/activity_main.xml

@@ -33,8 +33,9 @@
 
     </com.google.android.material.appbar.AppBarLayout>
 
-    <androidx.viewpager.widget.ViewPager
+    <androidx.viewpager2.widget.ViewPager2
         android:id="@+id/pager"
+        android:background="?attr/tab_page_margin_color"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:layout_below="@id/tab_layout"

app/src/main/res/layout/activity_search.xml

@@ -32,7 +32,7 @@
 
     </com.google.android.material.appbar.AppBarLayout>
 
-    <androidx.viewpager.widget.ViewPager
+    <androidx.viewpager2.widget.ViewPager2
         android:id="@+id/pages"
         android:layout_width="match_parent"
         android:layout_height="match_parent"

app/src/main/res/layout/activity_view_media.xml

@@ -6,7 +6,7 @@
     android:background="@android:color/black"
     android:orientation="vertical">
 
-    <com.keylesspalace.tusky.view.ImageViewPager
+    <androidx.viewpager2.widget.ViewPager2
         android:id="@+id/viewPager"
         android:layout_width="match_parent"
         android:layout_height="match_parent" />

app/src/main/res/layout/fragment_search.xml

@@ -4,20 +4,20 @@
     android:id="@+id/layoutRoot"
     android:layout_width="@dimen/timeline_width"
     android:layout_height="match_parent"
-    android:background="?attr/tab_page_margin_drawable">
+    android:background="?attr/tab_page_margin_color">
 
     <androidx.swiperefreshlayout.widget.SwipeRefreshLayout
-            android:id="@+id/swipeRefreshLayout"
+        android:id="@+id/swipeRefreshLayout"
-            android:layout_width="match_parent"
+        android:layout_width="match_parent"
-            android:layout_height="match_parent">
+        android:layout_height="match_parent">
 
         <androidx.recyclerview.widget.RecyclerView
-                android:id="@+id/searchRecyclerView"
+            android:id="@+id/searchRecyclerView"
-                android:layout_width="match_parent"
+            android:layout_width="match_parent"
-                android:layout_height="match_parent"
+            android:layout_height="match_parent"
-                android:layout_gravity="center"
+            android:layout_gravity="center"
-                android:background="?attr/window_background"
+            android:background="?attr/window_background"
-                tools:listitem="@layout/item_account"/>
+            tools:listitem="@layout/item_account" />
 
     </androidx.swiperefreshlayout.widget.SwipeRefreshLayout>
 

app/src/main/res/layout/fragment_timeline.xml

@@ -3,7 +3,9 @@
     xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
-    android:layout_height="match_parent">
+    android:layout_height="match_parent"
+    android:background="?attr/window_background">
+
     <androidx.swiperefreshlayout.widget.SwipeRefreshLayout
         android:id="@+id/swipeRefreshLayout"
         android:layout_width="match_parent"
@@ -29,23 +31,22 @@
         android:id="@+id/statusView"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
-        android:src="@android:color/transparent"
         android:visibility="gone"
         app:layout_constraintBottom_toBottomOf="parent"
         app:layout_constraintLeft_toLeftOf="parent"
         app:layout_constraintRight_toRightOf="parent"
         app:layout_constraintTop_toTopOf="parent"
-        tools:src="@drawable/elephant_error"
+        tools:visibility="visible" />
-        tools:visibility="visible"/>
+
     <androidx.core.widget.ContentLoadingProgressBar
         android:id="@+id/topProgressBar"
+        style="@style/Widget.AppCompat.ProgressBar.Horizontal"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
-        style="@style/Widget.AppCompat.ProgressBar.Horizontal"
-        app:layout_constraintTop_toTopOf="parent"
         android:indeterminate="true"
-        app:layout_constraintStart_toStartOf="parent"
+        android:visibility="gone"
-        app:layout_constraintEnd_toEndOf="parent"
         app:layout_constraintBottom_toTopOf="parent"
-        android:visibility="gone"/>
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toTopOf="parent" />
 </androidx.constraintlayout.widget.ConstraintLayout>

app/src/main/res/layout/fragment_timeline_notifications.xml

@@ -58,7 +58,8 @@
         <androidx.recyclerview.widget.RecyclerView
             android:id="@+id/recyclerView"
             android:layout_width="match_parent"
-            android:layout_height="match_parent" />
+            android:layout_height="match_parent"
+            android:background="?attr/window_background" />
 
     </androidx.swiperefreshlayout.widget.SwipeRefreshLayout>
 

app/src/main/res/layout/fragment_view_thread.xml

@@ -9,5 +9,7 @@
         android:id="@+id/recyclerView"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
+        android:background="?attr/window_background"
         android:scrollbars="vertical" />
+
 </androidx.swiperefreshlayout.widget.SwipeRefreshLayout>

app/src/main/res/values-night/styles.xml

@@ -41,7 +41,7 @@
         <item name="android:listDivider">@drawable/status_divider_dark</item>
         <item name="conversation_thread_line_drawable">@drawable/conversation_thread_line_dark</item>
         <item name="tab_icon_selected_tint">@color/tusky_blue</item>
-        <item name="tab_page_margin_drawable">@drawable/tab_page_margin_dark</item>
+        <item name="tab_page_margin_color">@color/tab_page_margin_dark</item>
         <item name="account_header_background_color">@color/color_background_dark</item>
         <item name="account_toolbar_icon_tint_uncollapsed">@color/toolbar_icon_dark</item>
         <item name="account_toolbar_icon_tint_collapsed">@color/account_toolbar_icon_collapsed_dark</item>

app/src/main/res/values/attrs.xml

@@ -25,7 +25,7 @@
     <attr name="media_preview_unloaded_drawable" format="reference" />
     <attr name="conversation_thread_line_drawable" format="reference" />
     <attr name="tab_icon_selected_tint" format="reference|color" />
-    <attr name="tab_page_margin_drawable" format="reference" />
+    <attr name="tab_page_margin_color" format="reference|color" />
     <attr name="account_header_background_color" format="reference|color" />
     <attr name="account_toolbar_icon_tint_uncollapsed" format="reference|color" />
     <attr name="account_toolbar_icon_tint_collapsed" format="reference|color" />

app/src/main/res/values/styles.xml

@@ -96,7 +96,7 @@
         <item name="conversation_thread_line_drawable">@drawable/conversation_thread_line_light
         </item>
         <item name="tab_icon_selected_tint">@color/tusky_blue</item>
-        <item name="tab_page_margin_drawable">@drawable/tab_page_margin_light</item>
+        <item name="tab_page_margin_color">@color/tab_page_margin_light</item>
         <item name="account_header_background_color">@color/color_primary_dark_light</item>
         <item name="account_toolbar_icon_tint_uncollapsed">@color/toolbar_icon_dark
         </item> <!--Default to dark on purpose, because header backgrounds with gradients are always dark.-->
@@ -200,7 +200,7 @@
         <item name="material_drawer_selected">@color/color_primary_black</item>
         <item name="material_drawer_selected_text">@color/text_color_primary_black</item>
         <item name="material_drawer_header_selection_text">@color/text_color_primary_black</item>
-        <item name="tab_page_margin_drawable">@drawable/tab_page_margin_black</item>
+        <item name="tab_page_margin_color">@color/tab_page_margin_black</item>
     </style>
 
     <style name="TuskyBlackTheme" parent="TuskyBlackThemeBase" />