Add a flag that shows a banner for old Scrollables (#7819)

Also, tweak Banner a bit so you can set the color and text style.
Also, cache the text painter between paints.

packages/flutter/lib/src/widgets/banner.dart

@@ -13,7 +13,9 @@ const double _kOffset = 40.0; // distance to bottom of banner, at a 45 degree an
 const double _kHeight = 12.0; // height of banner
 const double _kBottomOffset = _kOffset + 0.707 * _kHeight; // offset plus sqrt(2)/2 * banner height
 final Rect _kRect = new Rect.fromLTWH(-_kOffset, _kOffset - _kHeight, _kOffset * 2.0, _kHeight);
-const TextStyle _kTextStyles = const TextStyle(
+
+const Color _kColor = const Color(0xA0B71C1C);
+const TextStyle _kTextStyle = const TextStyle(
   color: const Color(0xFFFFFFFF),
   fontSize: _kHeight * 0.85,
   fontWeight: FontWeight.w900,
@@ -40,10 +42,17 @@ class BannerPainter extends CustomPainter {
   /// Creates a banner painter.
   ///
   /// The [message] and [location] arguments must not be null.
-  const BannerPainter({
+  BannerPainter({
     @required this.message,
-    @required this.location
-  });
+    @required this.location,
+    this.color: _kColor,
+    this.textStyle: _kTextStyle,
+  }) {
+    assert(message != null);
+    assert(location != null);
+    assert(color != null);
+    assert(textStyle != null);
+  }
 
   /// The message to show in the banner.
   final String message;
@@ -51,35 +60,55 @@ class BannerPainter extends CustomPainter {
   /// Where to show the banner (e.g., the upper right corder).
   final BannerLocation location;
 
-  @override
-  void paint(Canvas canvas, Size size) {
-    final Paint paintShadow = new Paint()
+  final Color color;
+
+  final TextStyle textStyle;
+
+  bool _prepared = false;
+  TextPainter _textPainter;
+  Paint _paintShadow;
+  Paint _paintBanner;
+
+  void _prepare() {
+    _paintShadow = new Paint()
       ..color = const Color(0x7F000000)
       ..maskFilter = new MaskFilter.blur(BlurStyle.normal, 4.0);
-    final Paint paintBanner = new Paint()
-      ..color = const Color(0xA0B71C1C);
+    _paintBanner = new Paint()
+      ..color = color;
+    _textPainter = new TextPainter(
+      text: new TextSpan(style: textStyle, text: message),
+      textAlign: TextAlign.center,
+    );
+    _prepared = true;
+  }
+
+  @override
+  void paint(Canvas canvas, Size size) {
+    if (!_prepared)
+      _prepare();
     canvas
       ..translate(_translationX(size.width), _translationY(size.height))
       ..rotate(_rotation)
-      ..drawRect(_kRect, paintShadow)
-      ..drawRect(_kRect, paintBanner);
-
+      ..drawRect(_kRect, _paintShadow)
+      ..drawRect(_kRect, _paintBanner);
     final double width = _kOffset * 2.0;
-    final TextPainter textPainter = new TextPainter(
-      text: new TextSpan(style: _kTextStyles, text: message),
-      textAlign: TextAlign.center
-    )..layout(minWidth: width, maxWidth: width);
-
-    textPainter.paint(canvas, _kRect.topLeft.toOffset() + new Offset(0.0, (_kRect.height - textPainter.height) / 2.0));
+    _textPainter.layout(minWidth: width, maxWidth: width);
+    _textPainter.paint(canvas, _kRect.topLeft.toOffset() + new Offset(0.0, (_kRect.height - _textPainter.height) / 2.0));
   }
 
   @override
-  bool shouldRepaint(BannerPainter oldPainter) => false;
+  bool shouldRepaint(BannerPainter oldPainter) {
+    return message != oldPainter.message
+        || location != oldPainter.location
+        || color != oldPainter.color
+        || textStyle != oldPainter.textStyle;
+  }
 
   @override
   bool hitTest(Point position) => false;
 
   double _translationX(double width) {
+    assert(location != null);
     switch (location) {
       case BannerLocation.bottomRight:
         return width - _kBottomOffset;
@@ -90,11 +119,11 @@ class BannerPainter extends CustomPainter {
       case BannerLocation.topLeft:
         return 0.0;
     }
-    assert(location != null);
     return null;
   }
 
   double _translationY(double height) {
+    assert(location != null);
     switch (location) {
       case BannerLocation.bottomRight:
       case BannerLocation.bottomLeft:
@@ -103,11 +132,11 @@ class BannerPainter extends CustomPainter {
       case BannerLocation.topLeft:
         return 0.0;
     }
-    assert(location != null);
     return null;
   }
 
   double get _rotation {
+    assert(location != null);
     switch (location) {
       case BannerLocation.bottomLeft:
       case BannerLocation.topRight:
@@ -116,7 +145,6 @@ class BannerPainter extends CustomPainter {
       case BannerLocation.topLeft:
         return -math.PI / 4.0;
     }
-    assert(location != null);
     return null;
   }
 }
@@ -136,11 +164,15 @@ class Banner extends StatelessWidget {
   Banner({
     Key key,
     this.child,
-    this.message,
-    this.location
+    @required this.message,
+    @required this.location,
+    this.color: _kColor,
+    this.textStyle: _kTextStyle,
   }) : super(key: key) {
     assert(message != null);
     assert(location != null);
+    assert(color != null);
+    assert(textStyle != null);
   }
 
   /// The widget to show behind the banner.
@@ -152,11 +184,22 @@ class Banner extends StatelessWidget {
   /// Where to show the banner (e.g., the upper right corder).
   final BannerLocation location;
 
+  /// The color of the banner.
+  final Color color;
+
+  /// The style of the text shown on the banner.
+  final TextStyle textStyle;
+
   @override
   Widget build(BuildContext context) {
     return new CustomPaint(
-      foregroundPainter: new BannerPainter(message: message, location: location),
-      child: child
+      foregroundPainter: new BannerPainter(
+        message: message,
+        location: location,
+        color: color,
+        textStyle: textStyle,
+      ),
+      child: child,
     );
   }
 }

packages/flutter/lib/src/widgets/debug.dart

@@ -57,6 +57,9 @@ bool debugPrintGlobalKeyedWidgetLifecycle = false;
 /// optimize your app, see https://fuchsia.googlesource.com/sysui/+/master/docs/performance.md
 bool debugProfileBuildsEnabled = false;
 
+/// Show banners for deprecated widgets.
+bool debugHighlightDeprecatedWidgets = false;
+
 Key _firstNonUniqueKey(Iterable<Widget> widgets) {
   Set<Key> keySet = new HashSet<Key>();
   for (Widget widget in widgets) {
@@ -184,7 +187,8 @@ bool debugAssertAllWidgetVarsUnset(String reason) {
         debugPrintBuildScope ||
         debugPrintScheduleBuildForStacks ||
         debugPrintGlobalKeyedWidgetLifecycle ||
-        debugProfileBuildsEnabled) {
+        debugProfileBuildsEnabled ||
+        debugHighlightDeprecatedWidgets) {
       throw new FlutterError(reason);
     }
     return true;

packages/flutter/lib/src/widgets/scrollable.dart

@@ -12,8 +12,10 @@ import 'package:flutter/physics.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/scheduler.dart';
 
+import 'banner.dart';
 import 'basic.dart';
 import 'clamp_overscrolls.dart';
+import 'debug.dart';
 import 'framework.dart';
 import 'gesture_detector.dart';
 import 'notification_listener.dart';
@@ -1386,15 +1388,24 @@ class ScrollableState<T extends Scrollable> extends State<T> with SingleTickerPr
 
   @override
   Widget build(BuildContext context) {
-    return new RawGestureDetector(
+    Widget result = new RawGestureDetector(
       key: _gestureDetectorKey,
       gestures: buildGestureDetectors(),
       behavior: HitTestBehavior.opaque,
       child: new IgnorePointer(
         ignoring: _scrollUnderway,
-        child: buildContent(context)
-      )
+        child: buildContent(context),
+      ),
     );
+    if (debugHighlightDeprecatedWidgets) {
+      result = new Banner(
+        message: 'OLD',
+        color: const Color(0xFF009000),
+        location: BannerLocation.bottomRight,
+        child: result,
+      );
+    }
+    return result;
   }
 
   /// Fixes up the gesture detector to listen to the appropriate

packages/flutter/test/widgets/banner_test.dart

@@ -18,7 +18,7 @@ class TestCanvas implements Canvas {
 
 void main() {
   test('A Banner with a location of topLeft paints in the top left', () {
-    BannerPainter bannerPainter = const BannerPainter(
+    BannerPainter bannerPainter = new BannerPainter(
       message:"foo",
       location: BannerLocation.topLeft
     );
@@ -44,7 +44,7 @@ void main() {
   });
 
   test('A Banner with a location of topRight paints in the top right', () {
-    BannerPainter bannerPainter = const BannerPainter(
+    BannerPainter bannerPainter = new BannerPainter(
       message:"foo",
       location: BannerLocation.topRight
     );
@@ -70,7 +70,7 @@ void main() {
   });
 
   test('A Banner with a location of bottomLeft paints in the bottom left', () {
-    BannerPainter bannerPainter = const BannerPainter(
+    BannerPainter bannerPainter = new BannerPainter(
       message:"foo",
       location: BannerLocation.bottomLeft
     );
@@ -96,7 +96,7 @@ void main() {
   });
 
   test('A Banner with a location of bottomRight paints in the bottom right', () {
-    BannerPainter bannerPainter = const BannerPainter(
+    BannerPainter bannerPainter = new BannerPainter(
       message:"foo",
       location: BannerLocation.bottomRight
     );