diff --git a/examples/widgets/container.dart b/examples/widgets/container.dart
index 51d471fc31..02537dc0e0 100644
--- a/examples/widgets/container.dart
+++ b/examples/widgets/container.dart
@@ -2,17 +2,17 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:sky/widgets.dart';
+import 'package:sky/src/fn3.dart';
 
-class ContainerApp extends App {
-  Widget build() {
+class ContainerApp extends StatelessComponent {
+  Widget build(BuildContext context) {
     return new Column([
         new Container(
           padding: new EdgeDims.all(10.0),
           margin: new EdgeDims.all(10.0),
           decoration: new BoxDecoration(backgroundColor: const Color(0xFFCCCCCC)),
           child: new NetworkImage(
-            src: "https://www.dartlang.org/logos/dart-logo.png",
+            src: "https://raw.githubusercontent.com/dart-lang/logos/master/logos_and_wordmarks/dart-logo.png",
             width: 300.0,
             height: 300.0
           )
diff --git a/examples/widgets/date_picker.dart b/examples/widgets/date_picker.dart
index f49c200b29..75dddb4850 100644
--- a/examples/widgets/date_picker.dart
+++ b/examples/widgets/date_picker.dart
@@ -2,27 +2,30 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:sky/widgets.dart';
+import 'package:sky/src/fn3.dart';
 import 'package:sky/material.dart';
 
 void main() => runApp(new DatePickerDemo());
 
-class DatePickerDemo extends App {
+class DatePickerDemo extends StatefulComponent {
+  DatePickerDemoState createState() => new DatePickerDemoState(this);
+}
 
-  DateTime _dateTime;
-
-  void initState() {
+class DatePickerDemoState extends ComponentState<DatePickerDemo> {
+  DatePickerDemoState(DatePickerDemo config) : super(config) {
     DateTime now = new DateTime.now();
     _dateTime = new DateTime(now.year, now.month, now.day);
   }
 
+  DateTime _dateTime;
+
   void _handleDateChanged(DateTime dateTime) {
     setState(() {
       _dateTime = dateTime;
     });
   }
 
-  Widget build() {
+  Widget build(BuildContext context) {
     return new Theme(
       data: new ThemeData(
         brightness: ThemeBrightness.light,
diff --git a/packages/flutter/lib/src/fn3/button_state.dart b/packages/flutter/lib/src/fn3/button_state.dart
index b35517832c..5612c85209 100644
--- a/packages/flutter/lib/src/fn3/button_state.dart
+++ b/packages/flutter/lib/src/fn3/button_state.dart
@@ -8,7 +8,7 @@ import 'package:sky/src/fn3/framework.dart';
 abstract class ButtonState<T extends StatefulComponent> extends ComponentState<T> {
   ButtonState(T config) : super(config);
 
-  bool highlight;
+  bool highlight = false;
 
   void _handlePointerDown(_) {
     setState(() {
diff --git a/packages/flutter/lib/src/fn3/material_button.dart b/packages/flutter/lib/src/fn3/material_button.dart
index 84ddbcd5ac..fb299b33ab 100644
--- a/packages/flutter/lib/src/fn3/material_button.dart
+++ b/packages/flutter/lib/src/fn3/material_button.dart
@@ -11,12 +11,14 @@ import 'package:sky/src/fn3/material.dart';
 
 // Rather than using this class directly, please use FlatButton or RaisedButton.
 abstract class MaterialButton extends StatefulComponent {
-  const MaterialButton({
+  MaterialButton({
     Key key,
     this.child,
     this.enabled: true,
     this.onPressed
-  }) : super(key: key);
+  }) : super(key: key) {
+    assert(enabled != null);
+  }
 
   final Widget child;
   final bool enabled;
diff --git a/packages/flutter/lib/src/fn3/raised_button.dart b/packages/flutter/lib/src/fn3/raised_button.dart
index a4ea191739..b134c62d3a 100644
--- a/packages/flutter/lib/src/fn3/raised_button.dart
+++ b/packages/flutter/lib/src/fn3/raised_button.dart
@@ -17,7 +17,9 @@ class RaisedButton extends MaterialButton {
   }) : super(key: key,
              child: child,
              enabled: enabled,
-             onPressed: onPressed);
+             onPressed: onPressed) {
+    assert(enabled != null);
+  }
 
   RaisedButtonState createState() => new RaisedButtonState(this);
 }
diff --git a/packages/flutter/lib/src/fn3/scaffold.dart b/packages/flutter/lib/src/fn3/scaffold.dart
index 9ae0c79eac..6d0935e25a 100644
--- a/packages/flutter/lib/src/fn3/scaffold.dart
+++ b/packages/flutter/lib/src/fn3/scaffold.dart
@@ -218,8 +218,9 @@ class ScaffoldElement extends RenderObjectElement<Scaffold> {
     super.mount(parent, newSlot);
     _children = new Map<ScaffoldSlots, Element>();
     for (ScaffoldSlots slot in ScaffoldSlots.values) {
-      _children[slot] = widget._children[slot].createElement()
-        ..mount(this, slot);
+      Element newChild = widget._children[slot]?.createElement();
+      _children[slot] = newChild;
+      newChild?.mount(this, slot);
     }
   }
 
diff --git a/packages/flutter/lib/src/fn3/scrollable.dart b/packages/flutter/lib/src/fn3/scrollable.dart
index 32aa5ec7ca..80a4db68bb 100644
--- a/packages/flutter/lib/src/fn3/scrollable.dart
+++ b/packages/flutter/lib/src/fn3/scrollable.dart
@@ -40,12 +40,7 @@ abstract class Scrollable extends StatefulComponent {
 }
 
 abstract class ScrollableState<T extends Scrollable> extends ComponentState<T> {
-  ScrollableState(T config) : super(config);
-
-  AnimatedSimulation _toEndAnimation; // See _startToEndAnimation()
-  ValueAnimation<double> _toOffsetAnimation; // Started by scrollTo()
-
-  void initState(BuildContext context) {
+  ScrollableState(T config) : super(config) {
     if (config.initialScrollOffset is double)
       _scrollOffset = config.initialScrollOffset;
     _toEndAnimation = new AnimatedSimulation(_setScrollOffset);
@@ -56,6 +51,9 @@ abstract class ScrollableState<T extends Scrollable> extends ComponentState<T> {
       });
   }
 
+  AnimatedSimulation _toEndAnimation; // See _startToEndAnimation()
+  ValueAnimation<double> _toOffsetAnimation; // Started by scrollTo()
+
   double _scrollOffset = 0.0;
   double get scrollOffset => _scrollOffset;