Get and show the list of conversations

lib/ui/screens/conversations_screen.dart

@@ -0,0 +1,87 @@
+import 'package:comunic/enums/load_error_level.dart';
+import 'package:comunic/helpers/conversations_helper.dart';
+import 'package:comunic/models/conversation.dart';
+import 'package:comunic/ui/tiles/conversation_tile.dart';
+import 'package:comunic/utils/intl_utils.dart';
+import 'package:comunic/utils/ui_utils.dart';
+import 'package:flutter/material.dart';
+
+/// Conversations screen
+///
+/// @author Pierre HUBERT
+
+class ConversationsScreen extends StatefulWidget {
+  @override
+  State<StatefulWidget> createState() => _ConversationScreenState();
+}
+
+class _ConversationScreenState extends State<ConversationsScreen> {
+  final ConversationsHelper _conversationsHelper = ConversationsHelper();
+  List<Conversation> _list;
+  LoadErrorLevel _error = LoadErrorLevel.NONE;
+  bool _loading = true;
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+    _loadConversations();
+  }
+
+  void setError(LoadErrorLevel err) => setState(() => _error = err);
+
+  void setLoading(bool loading) => setState(() => _loading = loading);
+
+  void gotLoadingError() {
+    setLoading(false);
+    setError(_list == null ? LoadErrorLevel.MAJOR : LoadErrorLevel.MINOR);
+  }
+
+  /// Load the list of conversations
+  Future<void> _loadConversations() async {
+    setError(LoadErrorLevel.NONE);
+    setLoading(true);
+
+    final list = await _conversationsHelper.downloadList();
+
+    if (list == null) return gotLoadingError();
+
+    //Save list
+    _list = list;
+
+    setLoading(false);
+  }
+
+  /// Build an error card
+  Widget _buildErrorCard() {
+    return buildErrorCard(
+      tr("Could not retrieve the list of conversations!"),
+      actions: <Widget>[
+        FlatButton(
+          onPressed: _loadConversations,
+          child: Text(
+            tr("Retry").toUpperCase(),
+            style: TextStyle(
+              color: Colors.white,
+            ),
+          ),
+        )
+      ],
+    );
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    if (_error == LoadErrorLevel.MAJOR) return _buildErrorCard();
+    if (_list == null) return buildCenteredProgressBar();
+
+    // Show the list of conversations
+    return ListView.builder(
+      itemBuilder: (context, index) {
+        return ConversationTile(
+          conversation: _list.elementAt(index),
+        );
+      },
+      itemCount: _list.length,
+    );
+  }
+}