Add kotlin extensions, enable R8 and fix errors.

app/build.gradle

@@ -143,9 +143,13 @@ dependencies {
     def supportVersion = '1.0.0'
     implementation "androidx.legacy:legacy-support-core-ui:$supportVersion"
     implementation "androidx.core:core:$supportVersion"
-    implementation "androidx.fragment:fragment:$supportVersion"
     implementation "androidx.appcompat:appcompat:1.1.0"
     implementation "androidx.cardview:cardview:1.0.0"
+    // KTX extensions
+    implementation "androidx.core:core-ktx:1.3.1"
+    implementation "androidx.fragment:fragment-ktx:1.2.5"
+
+
     implementation 'com.google.android.material:material:1.2.0-beta01'
     implementation "androidx.legacy:legacy-preference-v14:$supportVersion"
     implementation 'com.github.yukuku:ambilwarna:2.0.1'

app/src/main/java/com/etesync/syncadapter/ui/AccountListFragment.kt

@@ -32,7 +32,7 @@ import com.etesync.syncadapter.R
 class AccountListFragment : ListFragment(), LoaderManager.LoaderCallbacks<Array<Account>>, AdapterView.OnItemClickListener {
 
     override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
-        listAdapter = AccountListAdapter(context!!)
+        listAdapter = AccountListAdapter(requireContext())
 
         return inflater.inflate(R.layout.account_list, container, false)
     }
@@ -58,7 +58,7 @@ class AccountListFragment : ListFragment(), LoaderManager.LoaderCallbacks<Array<
     // loader
 
     override fun onCreateLoader(id: Int, args: Bundle?): Loader<Array<Account>> {
-        return AccountLoader(context!!)
+        return AccountLoader(requireContext())
     }
 
     override fun onLoadFinished(loader: Loader<Array<Account>>, accounts: Array<Account>) {

app/src/main/java/com/etesync/syncadapter/ui/CollectionMembersListFragment.kt

@@ -106,13 +106,13 @@ class CollectionMembersListFragment : ListFragment(), AdapterView.OnItemClickLis
     override fun onItemClick(parent: AdapterView<*>, view: View, position: Int, id: Long) {
         val member = listAdapter?.getItem(position) as JournalManager.Member
 
-        AlertDialog.Builder(activity!!)
+        AlertDialog.Builder(requireActivity())
                 .setIcon(R.drawable.ic_info_dark)
                 .setTitle(R.string.collection_members_remove_title)
                 .setMessage(getString(R.string.collection_members_remove, member.user))
                 .setPositiveButton(android.R.string.yes) { dialog, which ->
                     val frag = RemoveMemberFragment.newInstance(account, info, member.user!!)
-                    frag.show(fragmentManager!!, null)
+                    frag.show(requireFragmentManager(), null)
                 }
                 .setNegativeButton(android.R.string.no) { dialog, which -> }.show()
     }

app/src/main/java/com/etesync/syncadapter/ui/importlocal/ImportActivity.kt

@@ -108,9 +108,9 @@ class ImportActivity : BaseActivity(), SelectImportMethod, ResultFragment.OnImpo
             // This makes sure that the container activity has implemented
             // the callback interface. If not, it throws an exception
             try {
-                mSelectImportMethod = activity as SelectImportMethod?
+                mSelectImportMethod = activity as SelectImportMethod
             } catch (e: ClassCastException) {
-                throw ClassCastException(activity!!.toString() + " must implement MyInterface ")
+                throw ClassCastException(activity.toString() + " must implement MyInterface ")
             }
 
         }

app/src/main/java/com/etesync/syncadapter/ui/importlocal/ResultFragment.kt

@@ -19,7 +19,7 @@ class ResultFragment : DialogFragment() {
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
 
-        result = arguments!!.getSerializable(KEY_RESULT) as ImportResult
+        result = requireArguments().getSerializable(KEY_RESULT) as ImportResult
     }
 
     override fun onDismiss(dialog: DialogInterface) {
@@ -32,7 +32,7 @@ class ResultFragment : DialogFragment() {
 
     override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
         if (result!!.isFailed) {
-            return AlertDialog.Builder(activity!!)
+            return AlertDialog.Builder(requireActivity())
                     .setTitle(R.string.import_dialog_failed_title)
                     .setIcon(R.drawable.ic_error_dark)
                     .setMessage(getString(R.string.import_dialog_failed_body, result!!.e!!.localizedMessage))

app/src/main/java/com/etesync/syncadapter/ui/journalviewer/ListEntriesFragment.kt

@@ -88,7 +88,7 @@ class ListEntriesFragment : ListFragment(), AdapterView.OnItemClickListener {
 
     override fun onItemClick(parent: AdapterView<*>, view: View, position: Int, id: Long) {
         val entry = listAdapter?.getItem(position) as EntryEntity
-        startActivity(JournalItemActivity.newIntent(context!!, account, info, entry.content))
+        startActivity(JournalItemActivity.newIntent(requireContext(), account, info, entry.content))
     }
 
     internal inner class EntriesListAdapter(context: Context) : ArrayAdapter<EntryEntity>(context, R.layout.journal_viewer_list_item) {

app/src/main/java/com/etesync/syncadapter/ui/setup/DetectConfigurationFragment.kt

@@ -42,19 +42,19 @@ class DetectConfigurationFragment : DialogFragment(), LoaderManager.LoaderCallba
     }
 
     override fun onCreateLoader(id: Int, args: Bundle?): Loader<Configuration> {
-        return ServerConfigurationLoader(context!!, args!!.getParcelable(ARG_LOGIN_CREDENTIALS) as LoginCredentials)
+        return ServerConfigurationLoader(requireContext(), args!!.getParcelable(ARG_LOGIN_CREDENTIALS) as LoginCredentials)
     }
 
     override fun onLoadFinished(loader: Loader<Configuration>, data: Configuration?) {
         if (data != null) {
             if (data.isFailed)
             // no service found: show error message
-                fragmentManager!!.beginTransaction()
+                requireFragmentManager().beginTransaction()
                         .add(NothingDetectedFragment.newInstance(data.error!!.localizedMessage), null)
                         .commitAllowingStateLoss()
             else
             // service found: continue
-                fragmentManager!!.beginTransaction()
+                requireFragmentManager().beginTransaction()
                         .replace(android.R.id.content, EncryptionDetailsFragment.newInstance(data))
                         .addToBackStack(null)
                         .commitAllowingStateLoss()
@@ -76,7 +76,7 @@ class DetectConfigurationFragment : DialogFragment(), LoaderManager.LoaderCallba
                     .setMessage(R.string.login_wrong_username_or_password)
                     .setNeutralButton(R.string.login_view_logs) { dialog, which ->
                         val intent = DebugInfoActivity.newIntent(context, this::class.toString())
-                        intent.putExtra(DebugInfoActivity.KEY_LOGS, arguments!!.getString(KEY_LOGS))
+                        intent.putExtra(DebugInfoActivity.KEY_LOGS, requireArguments().getString(KEY_LOGS))
                         startActivity(intent)
                     }
                     .setPositiveButton(android.R.string.ok) { dialog, which ->