fix FragmentAdapter returning null fragments when activity was recreated (#1647)

* fix FragmentAdapter returning null fragments when activity was recreated

* remove unused import

* make activity in CustomFragmentStateAdapter private

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

@@ -21,33 +21,23 @@ 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
+import com.keylesspalace.tusky.util.CustomFragmentStateAdapter
 
 class AccountPagerAdapter(
         activity: FragmentActivity,
         private val accountId: String
-) : FragmentStateAdapter(activity) {
-
-    private val fragments = MutableList<WeakReference<Fragment>?>(TAB_COUNT) { null }
+) : CustomFragmentStateAdapter(activity) {
 
     override fun getItemCount() = TAB_COUNT
 
     override fun createFragment(position: Int): Fragment {
-        val fragment: Fragment = when (position) {
+        return 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() {

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

@@ -17,21 +17,16 @@ package com.keylesspalace.tusky.pager
 
 import androidx.fragment.app.Fragment
 import androidx.fragment.app.FragmentActivity
-import androidx.viewpager2.adapter.FragmentStateAdapter
 import com.keylesspalace.tusky.TabData
-import java.lang.ref.WeakReference
+import com.keylesspalace.tusky.util.CustomFragmentStateAdapter
 
-class MainPagerAdapter(val tabs: List<TabData>, activity: FragmentActivity) : FragmentStateAdapter(activity) {
-    private val fragments = MutableList<WeakReference<Fragment>?>(tabs.size) { null }
+class MainPagerAdapter(val tabs: List<TabData>, activity: FragmentActivity) : CustomFragmentStateAdapter(activity) {
 
     override fun createFragment(position: Int): Fragment {
         val tab = tabs[position]
-        val fragment = tab.fragment(tab.arguments)
-        fragments[position] = WeakReference(fragment)
-        return fragment
+        return tab.fragment(tab.arguments)
     }
 
     override fun getItemCount() = tabs.size
 
-    fun getFragment(position: Int): Fragment? = fragments[position]?.get()
 }

app/src/main/java/com/keylesspalace/tusky/util/CustomFragmentStateAdapter.kt

@@ -0,0 +1,28 @@
+/* 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.util
+
+import androidx.fragment.app.Fragment
+import androidx.fragment.app.FragmentActivity
+import androidx.viewpager2.adapter.FragmentStateAdapter
+
+abstract class CustomFragmentStateAdapter(
+        private val activity: FragmentActivity
+): FragmentStateAdapter(activity) {
+
+    fun getFragment(position: Int): Fragment?
+            = activity.supportFragmentManager.findFragmentByTag("f"  + getItemId(position))
+}