fix 1.17 lint rules

lib/src/bar.dart

@@ -373,7 +373,7 @@ class ConvexAppBarState extends State<ConvexAppBar>
     super.dispose();
   }
 
-  _updateTabController() {
+  void _updateTabController() {
     final TabController newController =
         widget.controller ?? DefaultTabController.of(context);
     _tabController?.removeListener(_handleTabControllerAnimationTick);
@@ -409,7 +409,7 @@ class ConvexAppBarState extends State<ConvexAppBar>
   @override
   Widget build(BuildContext context) {
     // take care of iPhoneX' safe area at bottom edge
-    final double additionalBottomPadding =
+    final additionalBottomPadding =
         math.max(MediaQuery.of(context).padding.bottom, 0.0);
     final convexIndex = isFixed() ? (widget.count ~/ 2) : _currentIndex;
     final active = isFixed() ? convexIndex == _currentIndex : true;
@@ -463,7 +463,7 @@ class ConvexAppBarState extends State<ConvexAppBar>
   bool isFixed() => widget.itemBuilder.fixed();
 
   Widget _barContent(double height, double paddingBottom, int curveTabIndex) {
-    List<Widget> children = [];
+    var children = <Widget>[];
     for (var i = 0; i < widget.count; i++) {
       if (i == curveTabIndex) {
         children.add(Expanded(child: Container()));

lib/src/convex_shape.dart

@@ -21,27 +21,27 @@ class ConvexNotchedRectangle extends NotchedShape {
 
     // The guest's shape is a circle bounded by the guest rectangle.
     // So the guest's radius is half the guest width.
-    final double notchRadius = guest.width / 2.0;
+    final notchRadius = guest.width / 2.0;
 
-    const double s1 = 15.0;
-    const double s2 = 1.0;
+    const s1 = 15.0;
+    const s2 = 1.0;
 
-    final double r = notchRadius;
-    final double a = -1.0 * r - s2;
-    final double b = host.top - guest.center.dy;
+    final r = notchRadius;
+    final a = -1.0 * r - s2;
+    final b = host.top - guest.center.dy;
 
-    final double n2 = math.sqrt(b * b * r * r * (a * a + b * b - r * r));
-    final double p2xA = ((a * r * r) - n2) / (a * a + b * b);
-    final double p2xB = ((a * r * r) + n2) / (a * a + b * b);
-    final double p2yA = -math.sqrt(r * r - p2xA * p2xA);
-    final double p2yB = -math.sqrt(r * r - p2xB * p2xB);
+    final n2 = math.sqrt(b * b * r * r * (a * a + b * b - r * r));
+    final p2xA = ((a * r * r) - n2) / (a * a + b * b);
+    final p2xB = ((a * r * r) + n2) / (a * a + b * b);
+    final p2yA = -math.sqrt(r * r - p2xA * p2xA);
+    final p2yB = -math.sqrt(r * r - p2xB * p2xB);
 
-    final List<Offset> p = List<Offset>(6);
+    final p = List<Offset>(6);
 
     // p0, p1, and p2 are the control points for segment A.
     p[0] = Offset(a - s1, b);
     p[1] = Offset(a, b);
-    final double cmp = b < 0 ? -1.0 : 1.0;
+    final cmp = b < 0 ? -1.0 : 1.0;
     p[2] = cmp * p2yA > cmp * p2yB ? Offset(p2xA, p2yA) : Offset(p2xB, p2yB);
 
     // p3, p4, and p5 are the control points for segment B, which is a mirror

lib/src/item.dart

@@ -24,6 +24,6 @@ class TabItem<T> {
     this.activeIcon,
     bool isIconBlend,
   })  : assert(icon is IconData || icon is Widget,
-            "TabItem only support IconData and Widget"),
+            'TabItem only support IconData and Widget'),
         blend = isIconBlend ?? (icon is IconData);
 }

lib/src/painter.dart

@@ -43,11 +43,11 @@ class ConvexPainter extends CustomPainter {
 
   @override
   void paint(Canvas canvas, Size size) {
-    Rect host = Rect.fromLTWH(0, 0, size.width, size.height);
-    Rect guest = Rect.fromLTWH(
+    var host = Rect.fromLTWH(0, 0, size.width, size.height);
+    var guest = Rect.fromLTWH(
         size.width * leftPercent.value - width / 2, top, width, height);
     _gradient.updateWith(_paint, size: host);
-    Path path = _shape.getOuterPath(host, guest);
+    var path = _shape.getOuterPath(host, guest);
     canvas.drawPath(path, _shadowPaint);
     canvas.drawPath(path, _paint);
   }

lib/src/reused_gradient.dart

@@ -18,7 +18,7 @@ class ReusedGradient {
   }
 
   /// Update the paint with provided size
-  updateWith(Paint paint, {Rect size}) {
+  void updateWith(Paint paint, {Rect size}) {
     if (size == _size) {
       return;
     }

lib/src/style/inner_builder.dart

@@ -23,6 +23,7 @@ abstract class InnerBuilder extends DelegateBuilder {
   /// Create style builder.
   InnerBuilder({this.items, this.activeColor, this.color});
 
+  /// Get style config
   StyleHook ofStyle(BuildContext context) {
     return StyleProvider.of(context)?.style ?? (_style ??= provideStyle());
   }

lib/src/style/transition_container.dart

@@ -16,7 +16,7 @@ class TransitionContainer extends StatefulWidget {
 
   /// Create transition with builder.
   TransitionContainer(
-      {this.builder, this.duration, this.disableAnimateWhenUpdate})
+      {@required this.builder, this.duration, this.disableAnimateWhenUpdate})
       : assert(builder != null);
 
   /// Wrap a widget with scale transition.