funwithflutter · August 10, 2021 22:05 · Aug 10, 2021 · Feb 28, 2020 · Feb 28, 2020
diff --git a/paint_demo.dart b/paint_demo.dart
@@ -2,19 +2,21 @@ import 'dart:math';
 
 import 'package:flutter/material.dart';
 
-void main() => runApp(MyApp());
+void main() => runApp(const MyApp());
 
 class MyApp extends StatelessWidget {
+  const MyApp({Key? key}) : super(key: key);
+
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
       showPerformanceOverlay: false,
       title: 'Paint Demo',
       home: Scaffold(
         appBar: AppBar(
-          title: Text('Paint Demo'),
+          title: const Text('Paint Demo'),
         ),
-        body: Center(
+        body: const Center(
           child: PaintDemo(),
         ),
       ),
@@ -23,21 +25,21 @@ class MyApp extends StatelessWidget {
 }
 
 class PaintDemo extends StatefulWidget {
-  PaintDemo({Key key}) : super(key: key);
+  const PaintDemo({Key? key}) : super(key: key);
 
   @override
   _PaintDemoState createState() => _PaintDemoState();
 }
 
 class _PaintDemoState extends State<PaintDemo>
     with SingleTickerProviderStateMixin {
-  AnimationController _controller;
-  CurvedAnimation _animation;
+  late AnimationController _controller;
+  late CurvedAnimation _animation;
 
   @override
   void initState() {
     _controller =
-        AnimationController(vsync: this, duration: Duration(seconds: 3));
+        AnimationController(vsync: this, duration: const Duration(seconds: 3));
     _animation = CurvedAnimation(parent: _controller, curve: Curves.slowMiddle);
 
     _controller.repeat();
@@ -60,7 +62,7 @@ class _PaintDemoState extends State<PaintDemo>
           child: child,
         );
       },
-      child: Container(
+      child: const SizedBox(
         width: 200,
         height: 75,
         child: Text('Loading...'),
@@ -75,7 +77,7 @@ class LinePainter extends CustomPainter {
   final double progress;
 
   static final linePaint = Paint()
-    ..color = Color(0xFFF4AC45)
+    ..color = const Color(0xFFF4AC45)
     ..style = PaintingStyle.stroke
     ..strokeWidth = 6
     ..strokeCap = StrokeCap.round;
@@ -90,9 +92,9 @@ class LinePainter extends CustomPainter {
     final point1 = max(0.0, widthProgress - _gap);
     final point2 = min(widthProgress + _gap, size.width);
 
-    canvas.drawLine(Offset(0, height), Offset(point1, height), linePaint);
-    canvas.drawLine(
-        Offset(point2, height), Offset(size.width, height), linePaint);
+    canvas
+      ..drawLine(Offset(0, height), Offset(point1, height), linePaint)
+      ..drawLine(Offset(point2, height), Offset(size.width, height), linePaint);
   }
 
   @override
@@ -102,4 +104,4 @@ class LinePainter extends CustomPainter {
     }
     return false;
   }
-}
+}
diff --git a/paint_demo.dart b/paint_demo.dart
@@ -44,6 +44,12 @@ class _PaintDemoState extends State<PaintDemo>
     super.initState();
   }
 
+  @override
+  void dispose() {
+    _controller.dispose();
+    super.dispose();
+  }
+
   @override
   Widget build(BuildContext context) {
     return AnimatedBuilder(
@@ -96,4 +102,4 @@ class LinePainter extends CustomPainter {
     }
     return false;
   }
-}
+}
diff --git a/paint_demo.dart b/paint_demo.dart
@@ -0,0 +1,99 @@
+import 'dart:math';
+
+import 'package:flutter/material.dart';
+
+void main() => runApp(MyApp());
+
+class MyApp extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      showPerformanceOverlay: false,
+      title: 'Paint Demo',
+      home: Scaffold(
+        appBar: AppBar(
+          title: Text('Paint Demo'),
+        ),
+        body: Center(
+          child: PaintDemo(),
+        ),
+      ),
+    );
+  }
+}
+
+class PaintDemo extends StatefulWidget {
+  PaintDemo({Key key}) : super(key: key);
+
+  @override
+  _PaintDemoState createState() => _PaintDemoState();
+}
+
+class _PaintDemoState extends State<PaintDemo>
+    with SingleTickerProviderStateMixin {
+  AnimationController _controller;
+  CurvedAnimation _animation;
+
+  @override
+  void initState() {
+    _controller =
+        AnimationController(vsync: this, duration: Duration(seconds: 3));
+    _animation = CurvedAnimation(parent: _controller, curve: Curves.slowMiddle);
+
+    _controller.repeat();
+    super.initState();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return AnimatedBuilder(
+      animation: _animation,
+      builder: (_, child) {
+        return CustomPaint(
+          painter: LinePainter(progress: _animation.value),
+          child: child,
+        );
+      },
+      child: Container(
+        width: 200,
+        height: 75,
+        child: Text('Loading...'),
+      ),
+    );
+  }
+}
+
+class LinePainter extends CustomPainter {
+  LinePainter({this.progress = 0.5});
+
+  final double progress;
+
+  static final linePaint = Paint()
+    ..color = Color(0xFFF4AC45)
+    ..style = PaintingStyle.stroke
+    ..strokeWidth = 6
+    ..strokeCap = StrokeCap.round;
+
+  static const _gap = 12.0;
+
+  @override
+  void paint(Canvas canvas, Size size) {
+    final height = size.height / 2;
+
+    final widthProgress = size.width * progress;
+    final point1 = max(0.0, widthProgress - _gap);
+    final point2 = min(widthProgress + _gap, size.width);
+
+    canvas.drawLine(Offset(0, height), Offset(point1, height), linePaint);
+    canvas.drawLine(
+        Offset(point2, height), Offset(size.width, height), linePaint);
+  }
+
+  @override
+  bool shouldRepaint(LinePainter oldDelegate) {
+    if (progress != oldDelegate.progress) {
+      return true;
+    }
+    return false;
+  }
+}