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/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
+    }
+}