Fix uninitialized fragment after restoring the activity (#237)

app/src/main/java/io/github/wulkanowy/data/db/AppDatabase.kt

@@ -6,16 +6,14 @@ import androidx.room.Room
 import androidx.room.RoomDatabase
 import androidx.room.RoomDatabase.JournalMode.TRUNCATE
 import androidx.room.TypeConverters
-import androidx.room.migration.Migration
-import androidx.sqlite.db.SupportSQLiteDatabase
 import io.github.wulkanowy.data.db.dao.AttendanceDao
 import io.github.wulkanowy.data.db.dao.AttendanceSummaryDao
 import io.github.wulkanowy.data.db.dao.ExamDao
 import io.github.wulkanowy.data.db.dao.GradeDao
 import io.github.wulkanowy.data.db.dao.GradeSummaryDao
-import io.github.wulkanowy.data.db.dao.MessagesDao
 import io.github.wulkanowy.data.db.dao.HomeworkDao
 import io.github.wulkanowy.data.db.dao.LuckyNumberDao
+import io.github.wulkanowy.data.db.dao.MessagesDao
 import io.github.wulkanowy.data.db.dao.NoteDao
 import io.github.wulkanowy.data.db.dao.SemesterDao
 import io.github.wulkanowy.data.db.dao.StudentDao
@@ -26,9 +24,9 @@ import io.github.wulkanowy.data.db.entities.AttendanceSummary
 import io.github.wulkanowy.data.db.entities.Exam
 import io.github.wulkanowy.data.db.entities.Grade
 import io.github.wulkanowy.data.db.entities.GradeSummary
-import io.github.wulkanowy.data.db.entities.Message
 import io.github.wulkanowy.data.db.entities.Homework
 import io.github.wulkanowy.data.db.entities.LuckyNumber
+import io.github.wulkanowy.data.db.entities.Message
 import io.github.wulkanowy.data.db.entities.Note
 import io.github.wulkanowy.data.db.entities.Semester
 import io.github.wulkanowy.data.db.entities.Student

app/src/main/java/io/github/wulkanowy/ui/base/BaseFragmentPagerAdapter.kt

@@ -1,6 +1,5 @@
 package io.github.wulkanowy.ui.base
 
-import android.view.ViewGroup
 import androidx.fragment.app.Fragment
 import androidx.fragment.app.FragmentManager
 import androidx.fragment.app.FragmentPagerAdapter
@@ -9,9 +8,10 @@ class BaseFragmentPagerAdapter(private val fragmentManager: FragmentManager) : F
 
     private val pages = mutableMapOf<Fragment, String?>()
 
-    private var containerId = 0
+    var containerId = 0
 
     fun getFragmentInstance(position: Int): Fragment? {
+        if (containerId == 0) throw IllegalArgumentException("Container id is 0")
         return fragmentManager.findFragmentByTag("android:switcher:$containerId:$position")
     }
 
@@ -23,11 +23,6 @@ class BaseFragmentPagerAdapter(private val fragmentManager: FragmentManager) : F
         this.pages.putAll(pages)
     }
 
-    override fun instantiateItem(container: ViewGroup, position: Int): Any {
-        containerId = container.id
-        return super.instantiateItem(container, position)
-    }
-
     override fun getItem(position: Int) = pages.keys.elementAt(position)
 
     override fun getCount() = pages.size

app/src/main/java/io/github/wulkanowy/ui/modules/grade/GradeFragment.kt

@@ -59,10 +59,13 @@ class GradeFragment : BaseSessionFragment(), GradeView, MainView.MainChildView,
     }
 
     override fun initView() {
-        pagerAdapter.addFragmentsWithTitle(mapOf(
+        pagerAdapter.apply {
+            containerId = gradeViewPager.id
+            addFragmentsWithTitle(mapOf(
                 GradeDetailsFragment.newInstance() to getString(R.string.all_details),
                 GradeSummaryFragment.newInstance() to getString(R.string.grade_menu_summary)
             ))
+        }
 
         gradeViewPager.run {
             adapter = pagerAdapter

app/src/main/java/io/github/wulkanowy/ui/modules/login/LoginActivity.kt

@@ -38,11 +38,14 @@ class LoginActivity : BaseActivity(), LoginView {
     }
 
     override fun initAdapter() {
-        loginAdapter.addFragments(listOf(
+        loginAdapter.apply {
+            containerId = loginViewpager.id
+            addFragments(listOf(
                 LoginFormFragment.newInstance(),
                 LoginSymbolFragment.newInstance(),
                 LoginStudentSelectFragment.newInstance()
             ))
+        }
 
         loginViewpager.run {
             offscreenPageLimit = 2

app/src/main/java/io/github/wulkanowy/ui/modules/message/MessageFragment.kt

@@ -46,11 +46,14 @@ class MessageFragment : BaseFragment(), MessageView, MainView.TitledView {
     }
 
     override fun initView() {
-        pagerAdapter.addFragmentsWithTitle(mapOf(
+        pagerAdapter.apply {
+            containerId = messageViewPager.id
+            addFragmentsWithTitle(mapOf(
                 MessageTabFragment.newInstance(RECEIVED) to getString(R.string.message_inbox),
                 MessageTabFragment.newInstance(SENT) to getString(R.string.message_sent),
                 MessageTabFragment.newInstance(TRASHED) to getString(R.string.message_trash)
             ))
+        }
 
         messageViewPager.run {
             adapter = pagerAdapter