diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8c9220b..7a949f7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## [2.0.0]
+
+* null safety.
+
 ## [1.0.0] - Stable
 
 * adapter: flutter version = v1.22
diff --git a/example/pubspec.lock b/example/pubspec.lock
index a24ef73..94f0941 100644
--- a/example/pubspec.lock
+++ b/example/pubspec.lock
@@ -7,63 +7,63 @@ packages:
       path: ".."
       relative: true
     source: path
-    version: "0.2.1"
+    version: "2.0.0"
   async:
     dependency: transitive
     description:
       name: async
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "2.5.0-nullsafety.1"
+    version: "2.6.0"
   boolean_selector:
     dependency: transitive
     description:
       name: boolean_selector
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "2.1.0-nullsafety.1"
+    version: "2.1.0"
   characters:
     dependency: transitive
     description:
       name: characters
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.1.0-nullsafety.3"
+    version: "1.1.0"
   charcode:
     dependency: transitive
     description:
       name: charcode
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.2.0-nullsafety.1"
+    version: "1.2.0"
   clock:
     dependency: transitive
     description:
       name: clock
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.1.0-nullsafety.1"
+    version: "1.1.0"
   collection:
     dependency: transitive
     description:
       name: collection
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.15.0-nullsafety.3"
+    version: "1.15.0"
   cupertino_icons:
     dependency: "direct main"
     description:
       name: cupertino_icons
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "0.1.3"
   fake_async:
     dependency: transitive
     description:
       name: fake_async
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.2.0-nullsafety.1"
+    version: "1.2.0"
   flutter:
     dependency: "direct main"
     description: flutter
@@ -78,23 +78,23 @@ packages:
     dependency: transitive
     description:
       name: matcher
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "0.12.10-nullsafety.1"
+    version: "0.12.10"
   meta:
     dependency: transitive
     description:
       name: meta
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.3.0-nullsafety.3"
+    version: "1.3.0"
   path:
     dependency: transitive
     description:
       name: path
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.8.0-nullsafety.1"
+    version: "1.8.0"
   sky_engine:
     dependency: transitive
     description: flutter
@@ -104,58 +104,58 @@ packages:
     dependency: transitive
     description:
       name: source_span
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.8.0-nullsafety.2"
+    version: "1.8.1"
   stack_trace:
     dependency: transitive
     description:
       name: stack_trace
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.10.0-nullsafety.1"
+    version: "1.10.0"
   stream_channel:
     dependency: transitive
     description:
       name: stream_channel
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "2.1.0-nullsafety.1"
+    version: "2.1.0"
   string_scanner:
     dependency: transitive
     description:
       name: string_scanner
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.1.0-nullsafety.1"
+    version: "1.1.0"
   term_glyph:
     dependency: transitive
     description:
       name: term_glyph
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.2.0-nullsafety.1"
+    version: "1.2.0"
   test_api:
     dependency: transitive
     description:
       name: test_api
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "0.2.19-nullsafety.2"
+    version: "0.3.0"
   typed_data:
     dependency: transitive
     description:
       name: typed_data
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.3.0-nullsafety.3"
+    version: "1.3.0"
   vector_math:
     dependency: transitive
     description:
       name: vector_math
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "2.1.0-nullsafety.3"
+    version: "2.1.0"
 sdks:
-  dart: ">=2.10.0-110 <2.11.0"
-  flutter: ">=1.20.0 <2.0.0"
+  dart: ">=2.13.0 <3.0.0"
+  flutter: ">=1.20.0"
diff --git a/lib/src/circular_state_progress_indicator.dart b/lib/src/circular_state_progress_indicator.dart
index 044caeb..908475c 100644
--- a/lib/src/circular_state_progress_indicator.dart
+++ b/lib/src/circular_state_progress_indicator.dart
@@ -14,21 +14,21 @@ class AirCircularStateProgressIndicator extends StatefulWidget {
   /// default value
   static const double DEFAULT_VALUE = 10;
 
-  Size _size;
-  double _min;
-  double _max;
-  num _value;
-  Color _pathColor;
-  Color _valueColor;
-  double _pathStrokeWidth;
-  double _valueStrokeWidth;
-  bool _filled;
-  bool _useCenter;
-  bool _roundCap;
+  Size? _size;
+  double? _min;
+  double? _max;
+  num? _value;
+  Color? _pathColor;
+  Color? _valueColor;
+  double? _pathStrokeWidth;
+  double? _valueStrokeWidth;
+  bool? _filled;
+  bool? _useCenter;
+  bool? _roundCap;
 
   /// constructor
   AirCircularStateProgressIndicator({
-    @required Size size,
+    required Size size,
     double min = LIMITED_MIN_VALUE,
     double max = LIMITED_MAX_VALUE,
     num value = DEFAULT_VALUE,
@@ -40,18 +40,10 @@ class AirCircularStateProgressIndicator extends StatefulWidget {
     bool useCenter = false,
     bool roundCap = true,
   }) {
-    assert(size != null);
     assert(min >= LIMITED_MIN_VALUE);
     assert(max <= LIMITED_MAX_VALUE);
     assert(value >= min);
     assert(value <= max);
-    assert(pathColor != null);
-    assert(valueColor != null);
-    assert(pathStrokeWidth != null);
-    assert(valueStrokeWidth != null);
-    assert(filled != null);
-    assert(useCenter != null);
-    assert(roundCap != null);
     _size = size;
     //value
     _value = value;
@@ -70,7 +62,7 @@ class AirCircularStateProgressIndicator extends StatefulWidget {
     _roundCap = roundCap;
 
     //The strokeWidth is zero when _filled is true,
-    if (_filled) {
+    if (_filled!) {
       _pathStrokeWidth = 0.0;
       _valueStrokeWidth = 0.0;
     }
@@ -88,35 +80,35 @@ class _CircularStateProgressIndicatorState
   @override
   Widget build(BuildContext context) {
     return CustomPaint(
-      size: widget._size,
+      size: widget._size!,
       painter: CircularProgressPaint._(
         shouldRepaint: false,
-        min: widget._min,
-        max: widget._max,
-        value: widget._value,
+        min: widget._min!,
+        max: widget._max!,
+        value: widget._value!,
         pathPaint: _getPathPaint(),
         valuePaint: _getValuePaint(),
-        useCenter: widget._useCenter,
+        useCenter: widget._useCenter!,
       ),
     );
   }
 
   Paint _getPathPaint() {
     return Paint()
-      ..color = widget._pathColor
-      ..strokeWidth = widget._pathStrokeWidth
-      ..strokeCap = widget._roundCap ? StrokeCap.round : StrokeCap.square
-      ..strokeJoin = widget._roundCap ? StrokeJoin.round : StrokeJoin.bevel
-      ..style = widget._filled ? PaintingStyle.fill : PaintingStyle.stroke;
+      ..color = widget._pathColor!
+      ..strokeWidth = widget._pathStrokeWidth!
+      ..strokeCap = widget._roundCap! ? StrokeCap.round : StrokeCap.square
+      ..strokeJoin = widget._roundCap! ? StrokeJoin.round : StrokeJoin.bevel
+      ..style = widget._filled! ? PaintingStyle.fill : PaintingStyle.stroke;
   }
 
   Paint _getValuePaint() {
     return Paint()
-      ..color = widget._valueColor
-      ..strokeWidth = widget._valueStrokeWidth
-      ..strokeCap = widget._roundCap ? StrokeCap.round : StrokeCap.square
-      ..strokeJoin = widget._roundCap ? StrokeJoin.round : StrokeJoin.bevel
-      ..style = widget._filled ? PaintingStyle.fill : PaintingStyle.stroke;
+      ..color = widget._valueColor!
+      ..strokeWidth = widget._valueStrokeWidth!
+      ..strokeCap = widget._roundCap! ? StrokeCap.round : StrokeCap.square
+      ..strokeJoin = widget._roundCap! ? StrokeJoin.round : StrokeJoin.bevel
+      ..style = widget._filled! ? PaintingStyle.fill : PaintingStyle.stroke;
   }
 }
 
@@ -132,24 +124,24 @@ class CircularProgressPaint extends CustomPainter with ProgressMixin {
   /// start angle
   static const double DEFAULT_START_ANGLE = -1.5;
 
-  bool _shouldRepaint;
-  num _min;
-  num _max;
-  num _value;
-  Paint _pathPaint;
-  Paint _valuePaint;
-  bool _useCenter;
+  bool? _shouldRepaint;
+  num? _min;
+  num? _max;
+  num? _value;
+  Paint? _pathPaint;
+  Paint? _valuePaint;
+  bool? _useCenter;
 
   /// CircularProgressPaint
   ///
   CircularProgressPaint._({
-    @required bool shouldRepaint,
-    @required num min,
-    @required num max,
-    @required num value,
-    @required Paint pathPaint,
-    @required Paint valuePaint,
-    @required bool useCenter,
+    required bool shouldRepaint,
+    required num min,
+    required num max,
+    required num value,
+    required Paint pathPaint,
+    required Paint valuePaint,
+    required bool useCenter,
   }) {
     _shouldRepaint = shouldRepaint;
     _min = min;
@@ -162,26 +154,28 @@ class CircularProgressPaint extends CustomPainter with ProgressMixin {
   @override
   void paint(Canvas canvas, Size size) {
     // draw progress path
-    drawProgressPath(canvas: canvas, paint: _pathPaint, size: size);
+    drawProgressPath(canvas: canvas, paint: _pathPaint!, size: size);
 
     // draw progress value
-    drawProgressValue(canvas: canvas, paint: _valuePaint, size: size);
+    drawProgressValue(canvas: canvas, paint: _valuePaint!, size: size);
   }
 
   @override
   bool shouldRepaint(CustomPainter oldDelegate) {
-    return _shouldRepaint;
+    return _shouldRepaint!;
   }
 
   @override
-  drawProgressPath({Canvas canvas, Paint paint, Size size}) {
+  drawProgressPath(
+      {required Canvas canvas, required Paint paint, required Size size}) {
     Offset center = _getOffset(size: size);
     double radius = _getRadius(size: size);
     canvas.drawCircle(center, radius, paint);
   }
 
   @override
-  drawProgressValue({Canvas canvas, Paint paint, Size size}) {
+  drawProgressValue(
+      {required Canvas canvas, required Paint paint, required Size size}) {
     Offset center = _getOffset(size: size);
     double radius = _getRadius(size: size);
     canvas.drawArc(Rect.fromCircle(center: center, radius: radius),
@@ -196,38 +190,38 @@ class CircularProgressPaint extends CustomPainter with ProgressMixin {
     if (_value == _min) {
       return 0;
     }
-    if (_value > _min && _value < maxHalf) {
-      return (_value * 0.0612);
+    if (_value! > _min! && _value! < maxHalf!) {
+      return (_value! * 0.0612);
     }
     if (_value == maxHalf) {
-      return _value * 0.0600;
+      return _value! * 0.0600;
     }
-    if (_value > maxHalf && _value < _max) {}
-    if (_value == _max) {
-      return maxSweepAngleIncludeCap;
+    if (_value! > maxHalf && _value! < _max!) {}
+    if (_value! == _max!) {
+      return maxSweepAngleIncludeCap.toDouble();
     }
-    return (_value * 0.0615);
+    return (_value! * 0.0615);
   }
 
   /// the half of max value
-  get maxHalf => _max / 2;
+  get maxHalf => _max! / 2;
 
   /// useCenter
   /// whether use center point close the path.
   bool get useCenter {
-    return _useCenter;
+    return _useCenter!;
   }
 
   /// circular radius
-  double _getRadius({Size size}) {
+  double _getRadius({required Size size}) {
     double radius =
         size.width / 2 < size.height / 2 ? size.width / 2 : size.height / 2;
-    radius -= _valuePaint.strokeWidth / 2;
+    radius -= _valuePaint!.strokeWidth / 2;
     return radius;
   }
 
   /// point
-  Offset _getOffset({Size size}) {
+  Offset _getOffset({required Size size}) {
     return Offset(size.width / 2, size.height / 2);
   }
 }
diff --git a/lib/src/dashboard_state_progress_indicator.dart b/lib/src/dashboard_state_progress_indicator.dart
index e52f19b..01df6f9 100644
--- a/lib/src/dashboard_state_progress_indicator.dart
+++ b/lib/src/dashboard_state_progress_indicator.dart
@@ -18,23 +18,23 @@ const double DEFAULT_STROKE_WIDTH = 5;
 /// DashboardStateProgressIndicator
 // ignore: must_be_immutable
 class AirDashboardStateProgressIndicator extends StatefulWidget {
-  Size _size;
-  double _min;
-  double _max;
-  num _value;
-  Color _pathColor;
-  Color _valueColor;
-  double _pathStrokeWidth;
-  double _valueStrokeWidth;
-  bool _filled;
-  bool _useCenter;
-  bool _roundCap;
-
-  double _gapDegree;
+  Size? _size;
+  double? _min;
+  double? _max;
+  num? _value;
+  Color? _pathColor;
+  Color? _valueColor;
+  double? _pathStrokeWidth;
+  double? _valueStrokeWidth;
+  bool? _filled;
+  bool? _useCenter;
+  bool? _roundCap;
+
+  double? _gapDegree;
 
   /// constructor
   AirDashboardStateProgressIndicator({
-    Size size,
+    required Size size,
     double min = LIMITED_MIN_VALUE,
     double max = LIMITED_MAX_VALUE,
     num value = DEFAULT_VALUE,
@@ -47,20 +47,12 @@ class AirDashboardStateProgressIndicator extends StatefulWidget {
     bool useCenter = false,
     bool roundCap = true,
   }) {
-    assert(size != null);
     assert(min >= LIMITED_MIN_VALUE);
     assert(max <= LIMITED_MAX_VALUE);
     assert(value >= min);
     assert(value <= max);
     assert(gapDegree >= LIMITED_MIN_GAP_DEGREE);
     assert(gapDegree <= LIMITED_MAX_GAP_DEGREE);
-    assert(pathColor != null);
-    assert(valueColor != null);
-    assert(pathStrokeWidth != null);
-    assert(valueStrokeWidth != null);
-    assert(filled != null);
-    assert(useCenter != null);
-    assert(roundCap != null);
     _size = size;
     //value >= 0.00,value<=100
     _value = value;
@@ -81,7 +73,7 @@ class AirDashboardStateProgressIndicator extends StatefulWidget {
     _useCenter = useCenter;
 
     //The strokeWidth is zero when _filled is true,
-    if (_filled) {
+    if (_filled!) {
       _pathStrokeWidth = 0.0;
       _valueStrokeWidth = 0.0;
     }
@@ -99,37 +91,37 @@ class _DashboardStateProgressIndicatorState
   @override
   Widget build(BuildContext context) {
     return CustomPaint(
-      size: widget._size,
+      size: widget._size!,
       painter: DashboardProgressPaint._(
         shouldRepaint: false,
         division: LIMITED_MAX_GAP_DEGREE ~/ UNIT_GAP_DEGREE,
-        min: widget._min,
-        max: widget._max,
-        value: widget._value,
-        gapDegree: widget._gapDegree,
+        min: widget._min!,
+        max: widget._max!,
+        value: widget._value!,
+        gapDegree: widget._gapDegree!,
         pathPaint: _getPathPaint(),
         valuePaint: _getValuePaint(),
-        useCenter: widget._useCenter,
+        useCenter: widget._useCenter!,
       ),
     );
   }
 
   Paint _getPathPaint() {
     return Paint()
-      ..color = widget._pathColor
-      ..strokeWidth = widget._pathStrokeWidth
-      ..strokeCap = widget._roundCap ? StrokeCap.round : StrokeCap.square
-      ..strokeJoin = widget._roundCap ? StrokeJoin.round : StrokeJoin.bevel
-      ..style = widget._filled ? PaintingStyle.fill : PaintingStyle.stroke;
+      ..color = widget._pathColor!
+      ..strokeWidth = widget._pathStrokeWidth!
+      ..strokeCap = widget._roundCap! ? StrokeCap.round : StrokeCap.square
+      ..strokeJoin = widget._roundCap! ? StrokeJoin.round : StrokeJoin.bevel
+      ..style = widget._filled! ? PaintingStyle.fill : PaintingStyle.stroke;
   }
 
   Paint _getValuePaint() {
     return Paint()
-      ..color = widget._valueColor
-      ..strokeWidth = widget._valueStrokeWidth
-      ..strokeCap = widget._roundCap ? StrokeCap.round : StrokeCap.square
-      ..strokeJoin = widget._roundCap ? StrokeJoin.round : StrokeJoin.bevel
-      ..style = widget._filled ? PaintingStyle.fill : PaintingStyle.stroke;
+      ..color = widget._valueColor!
+      ..strokeWidth = widget._valueStrokeWidth!
+      ..strokeCap = widget._roundCap! ? StrokeCap.round : StrokeCap.square
+      ..strokeJoin = widget._roundCap! ? StrokeJoin.round : StrokeJoin.bevel
+      ..style = widget._filled! ? PaintingStyle.fill : PaintingStyle.stroke;
   }
 }
 
@@ -140,28 +132,28 @@ class DashboardProgressPaint extends CustomPainter with ProgressMixin {
   final num maxSweepAngle = 6.5;
   final num circleMaxSweepAngle = 6.1275;
   final num minSweepAngle = 1.0;
-  bool _shouldRepaint;
-  num _min;
-  num _max;
-  num _value;
-  Paint _pathPaint;
-  Paint _valuePaint;
-  bool _useCenter;
-  double _gapDegree;
-  int _division;
+  bool? _shouldRepaint;
+  num? _min;
+  num? _max;
+  num? _value;
+  Paint? _pathPaint;
+  Paint? _valuePaint;
+  bool? _useCenter;
+  double? _gapDegree;
+  int? _division;
 
   /// CircularProgressPaint
   ///
   DashboardProgressPaint._({
-    @required bool shouldRepaint,
-    @required int division,
-    @required num min,
-    @required num max,
-    @required num value,
-    @required double gapDegree,
-    @required Paint pathPaint,
-    @required Paint valuePaint,
-    @required bool useCenter,
+    required bool shouldRepaint,
+    required int division,
+    required num min,
+    required num max,
+    required num value,
+    required double gapDegree,
+    required Paint pathPaint,
+    required Paint valuePaint,
+    required bool useCenter,
   }) {
     _shouldRepaint = shouldRepaint;
     _division = division;
@@ -176,19 +168,20 @@ class DashboardProgressPaint extends CustomPainter with ProgressMixin {
   @override
   void paint(Canvas canvas, Size size) {
     // draw progress path
-    drawProgressPath(canvas: canvas, paint: _pathPaint, size: size);
+    drawProgressPath(canvas: canvas, paint: _pathPaint!, size: size);
 
     // draw progress value
-    drawProgressValue(canvas: canvas, paint: _valuePaint, size: size);
+    drawProgressValue(canvas: canvas, paint: _valuePaint!, size: size);
   }
 
   @override
   bool shouldRepaint(CustomPainter oldDelegate) {
-    return _shouldRepaint;
+    return _shouldRepaint!;
   }
 
   @override
-  drawProgressPath({Canvas canvas, Paint paint, Size size}) {
+  drawProgressPath(
+      {required Canvas canvas, required Paint paint, required Size size}) {
     Offset center = _getOffset(size: size);
     double radius = _getRadius(size: size);
 
@@ -197,18 +190,19 @@ class DashboardProgressPaint extends CustomPainter with ProgressMixin {
   }
 
   @override
-  drawProgressValue({Canvas canvas, Paint paint, Size size}) {
+  drawProgressValue(
+      {required Canvas canvas, required Paint paint, required Size size}) {
     Offset center = _getOffset(size: size);
     double radius = _getRadius(size: size);
     canvas.drawArc(Rect.fromCircle(center: center, radius: radius),
         _getStartAngle(), _getValueSweepAngle(), useCenter, paint);
   }
 
-  double get gapDegree => _gapDegree;
-  int get division => _division;
+  double get gapDegree => _gapDegree!;
+  int get division => _division!;
 
   double _getCircleMaxAngle() {
-    return circleMaxSweepAngle;
+    return circleMaxSweepAngle.toDouble();
   }
 
   double _getStartAngle() {
@@ -216,7 +210,7 @@ class DashboardProgressPaint extends CustomPainter with ProgressMixin {
   }
 
   double _getGapDegreeSweepAngle() {
-    return (maxSweepAngle / division) * _gapDegree;
+    return (maxSweepAngle / division) * _gapDegree!;
   }
 
   double _getMaxSweepAngle() {
@@ -224,23 +218,23 @@ class DashboardProgressPaint extends CustomPainter with ProgressMixin {
   }
 
   double _getValueSweepAngle() {
-    return _getMaxSweepAngle() / _max * _value;
+    return _getMaxSweepAngle() / _max! * _value!;
   }
 
   /// useCenter
   /// whether use center point close the path.
   bool get useCenter {
-    return _useCenter;
+    return _useCenter!;
   }
 
-  double _getRadius({Size size}) {
+  double _getRadius({required Size size}) {
     double radius =
         size.width / 2 < size.height / 2 ? size.width / 2 : size.height / 2;
-    radius -= _valuePaint.strokeWidth / 2;
+    radius -= _valuePaint!.strokeWidth / 2;
     return radius;
   }
 
-  Offset _getOffset({Size size}) {
+  Offset _getOffset({required Size size}) {
     return Offset(size.width / 2, size.height / 2);
   }
 }
diff --git a/lib/src/linear_state_progress_indicator.dart b/lib/src/linear_state_progress_indicator.dart
index a9b2222..f28443e 100644
--- a/lib/src/linear_state_progress_indicator.dart
+++ b/lib/src/linear_state_progress_indicator.dart
@@ -10,20 +10,20 @@ const double LINEAR_DEFAULT_VALUE = 10;
 ///
 // ignore: must_be_immutable
 class AirLinearStateProgressIndicator extends StatefulWidget {
-  double _value;
-  double _min;
-  double _max;
-  Size _size;
-  bool _shouldRepaint;
-  bool _roundCap;
-  Color _pathColor;
-  Color _valueColor;
-  double _pathStrokeWidth = 5;
-  double _valueStrokeWidth = 5;
+  double? _value;
+  double? _min;
+  double? _max;
+  Size? _size;
+  bool? _shouldRepaint;
+  bool? _roundCap;
+  Color? _pathColor;
+  Color? _valueColor;
+  double? _pathStrokeWidth = 5;
+  double? _valueStrokeWidth = 5;
 
   /// constructor
   AirLinearStateProgressIndicator({
-    @required Size size,
+    required Size size,
     double min = LINEAR_LIMITED_MIN_VALUE,
     double max = LINEAR_LIMITED_MAX_VALUE,
     double value = LINEAR_DEFAULT_VALUE,
@@ -31,20 +31,13 @@ class AirLinearStateProgressIndicator extends StatefulWidget {
     Color valueColor = Colors.green,
     bool roundCap = true,
     bool shouldRepaint = false,
-    double pathStrokeWidth,
-    double valueStrokeWidth,
+    double? pathStrokeWidth,
+    double? valueStrokeWidth,
   }) {
-    assert(size != null);
     assert(min >= LINEAR_LIMITED_MIN_VALUE);
     assert(max <= LINEAR_LIMITED_MAX_VALUE);
     assert(value >= min);
     assert(value <= max);
-    assert(pathColor != null);
-    assert(valueColor != null);
-    assert(roundCap != null);
-    assert(shouldRepaint != null);
-    assert(pathStrokeWidth != null);
-    assert(valueStrokeWidth != null);
     _size = size;
     _min = min;
     _max = max;
@@ -72,17 +65,17 @@ class _LinearStateProgressIndicatorState
   @override
   Widget build(BuildContext context) {
     return CustomPaint(
-      size: widget._size,
+      size: widget._size!,
       painter: LinearProgressPainter._(
-        shouldRepaint: widget._shouldRepaint,
-        roundCap: widget._roundCap,
-        min: widget._min,
-        max: widget._max,
-        value: widget._value,
-        pathColor: widget._pathColor,
-        valueColor: widget._valueColor,
-        pathStrokeWidth: widget._pathStrokeWidth,
-        valueStrokeWidth: widget._valueStrokeWidth,
+        shouldRepaint: widget._shouldRepaint!,
+        roundCap: widget._roundCap!,
+        min: widget._min!,
+        max: widget._max!,
+        value: widget._value!,
+        pathColor: widget._pathColor!,
+        valueColor: widget._valueColor!,
+        pathStrokeWidth: widget._pathStrokeWidth!,
+        valueStrokeWidth: widget._valueStrokeWidth!,
       ),
     );
   }
@@ -90,29 +83,29 @@ class _LinearStateProgressIndicatorState
 
 /// LinearProgressPainter
 class LinearProgressPainter extends CustomPainter with ProgressMixin {
-  bool _shouldRepaint;
-  bool _roundCap;
-  double _min;
-  double _max;
-  double _value;
+  bool? _shouldRepaint;
+  bool? _roundCap;
+  double? _min;
+  double? _max;
+  double? _value;
 
-  Color _pathColor;
-  Color _valueColor;
+  Color? _pathColor;
+  Color? _valueColor;
 
-  double _pathStrokeWidth;
-  double _valueStrokeWidth;
+  double? _pathStrokeWidth;
+  double? _valueStrokeWidth;
 
   /// constructor
   LinearProgressPainter._({
-    @required bool shouldRepaint,
-    @required bool roundCap,
-    @required double min,
-    @required double max,
-    @required double value,
-    @required Color pathColor,
-    @required Color valueColor,
-    @required double pathStrokeWidth,
-    @required double valueStrokeWidth,
+    required bool shouldRepaint,
+    required bool roundCap,
+    required double min,
+    required double max,
+    required double value,
+    required Color pathColor,
+    required Color valueColor,
+    required double pathStrokeWidth,
+    required double valueStrokeWidth,
   }) {
     //should repaint
     _shouldRepaint = shouldRepaint;
@@ -138,11 +131,12 @@ class LinearProgressPainter extends CustomPainter with ProgressMixin {
 
   @override
   bool shouldRepaint(CustomPainter oldDelegate) {
-    return _shouldRepaint;
+    return _shouldRepaint!;
   }
 
   @override
-  drawProgressPath({Canvas canvas, Paint paint, Size size}) {
+  drawProgressPath(
+      {required Canvas canvas, required Paint paint, required Size size}) {
     double heightCenter = size.height / 2;
     double width = size.width;
 
@@ -153,7 +147,8 @@ class LinearProgressPainter extends CustomPainter with ProgressMixin {
   }
 
   @override
-  drawProgressValue({Canvas canvas, Paint paint, Size size}) {
+  drawProgressValue(
+      {required Canvas canvas, required Paint paint, required Size size}) {
     double heightCenter = size.height / 2;
 
     Offset startPoint = Offset(0, heightCenter);
@@ -164,20 +159,20 @@ class LinearProgressPainter extends CustomPainter with ProgressMixin {
 
   Paint _getDrawPathPaint() {
     return Paint()
-      ..color = _pathColor
-      ..strokeWidth = _pathStrokeWidth
-      ..strokeCap = _roundCap ? StrokeCap.round : StrokeCap.square;
+      ..color = _pathColor!
+      ..strokeWidth = _pathStrokeWidth!
+      ..strokeCap = _roundCap! ? StrokeCap.round : StrokeCap.square;
   }
 
   Paint _getDrawValuePaint() {
     return Paint()
-      ..color = _valueColor
-      ..strokeWidth = _valueStrokeWidth
-      ..strokeCap = _roundCap ? StrokeCap.round : StrokeCap.square;
+      ..color = _valueColor!
+      ..strokeWidth = _valueStrokeWidth!
+      ..strokeCap = _roundCap! ? StrokeCap.round : StrokeCap.square;
   }
 
-  double _getDrawWidthValue({@required Size size}) {
-    double drawWidthValue = size.width * ((_value - _min) / (_max - _min));
+  double _getDrawWidthValue({required Size size}) {
+    double drawWidthValue = size.width * ((_value! - _min!) / (_max! - _min!));
 
     //range size
     drawWidthValue = drawWidthValue < 0 ? 0 : drawWidthValue;
diff --git a/lib/src/progress_mixin.dart b/lib/src/progress_mixin.dart
index 7d552ed..524d569 100644
--- a/lib/src/progress_mixin.dart
+++ b/lib/src/progress_mixin.dart
@@ -3,8 +3,10 @@ import 'dart:ui';
 /// ProgressMixin
 mixin ProgressMixin {
   /// draw progress path
-  drawProgressPath({Canvas canvas, Paint paint, Size size});
+  drawProgressPath(
+      {required Canvas canvas, required Paint paint, required Size size});
 
   /// draw progress value
-  drawProgressValue({Canvas canvas, Paint paint, Size size});
+  drawProgressValue(
+      {required Canvas canvas, required Paint paint, required Size size});
 }
diff --git a/lib/src/step_state_progress_indicator.dart b/lib/src/step_state_progress_indicator.dart
index 857503e..c2a5a2f 100644
--- a/lib/src/step_state_progress_indicator.dart
+++ b/lib/src/step_state_progress_indicator.dart
@@ -17,16 +17,16 @@ class AirStepStateProgressIndicator extends StatefulWidget {
   final int stepCount;
   final int stepValue;
 
-  double _pathStrokeWidth;
-  double _valueStrokeWidth;
-  double _spaceWidth;
+  double? _pathStrokeWidth;
+  double? _valueStrokeWidth;
+  double? _spaceWidth;
 
-  Color _pathColor;
-  Color _valueColor;
+  Color? _pathColor;
+  Color? _valueColor;
 
   /// constructor
   AirStepStateProgressIndicator({
-    this.size,
+    required this.size,
     this.stepCount = DEFAULT_STEP_COUNT,
     this.stepValue = DEFAULT_STEP_VALUE,
     double pathStrokeWidth = DEFAULT_STROKE_WIDTH,
@@ -35,17 +35,9 @@ class AirStepStateProgressIndicator extends StatefulWidget {
     Color pathColor = Colors.grey,
     Color valueColor = Colors.green,
   }) {
-    assert(size != null);
-    assert(stepCount != null);
     assert(stepCount > LIMITED_STEP_MIN_VALUE);
-    assert(stepValue != null);
     assert(stepValue >= LIMITED_STEP_MIN_VALUE);
     assert(stepValue <= stepCount);
-    assert(pathStrokeWidth != null);
-    assert(valueStrokeWidth != null);
-    assert(spaceWidth != null);
-    assert(pathColor != null);
-    assert(valueColor != null);
 
     //stroke width
     _pathStrokeWidth = pathStrokeWidth;
@@ -87,31 +79,31 @@ class _StepStateProgressIndicator extends State<AirStepStateProgressIndicator> {
 
 /// StepProgressPainter
 class StepProgressPainter extends CustomPainter with ProgressMixin {
-  bool _shouldRepaint;
-  int _stepCount;
-  int _stepValue;
+  bool? _shouldRepaint;
+  int? _stepCount;
+  int? _stepValue;
 
-  double _pathStrokeWidth;
-  double _valueStrokeWidth;
+  double? _pathStrokeWidth;
+  double? _valueStrokeWidth;
 
-  double _spaceWidth;
+  double? _spaceWidth;
 
-  Color _valueColor;
-  Color _pathColor;
+  Color? _valueColor;
+  Color? _pathColor;
 
-  bool _roundCap;
+  bool? _roundCap;
 
   /// constructor
   StepProgressPainter._({
-    @required bool shouldRepaint,
-    @required int stepCount,
-    @required int stepValue,
-    double pathStrokeWidth,
-    double valueStrokeWidth,
-    double spaceWidth,
-    Color pathColor,
-    Color valueColor,
-    bool roundCap,
+    required bool shouldRepaint,
+    required int stepCount,
+    required int stepValue,
+    double? pathStrokeWidth,
+    double? valueStrokeWidth,
+    double? spaceWidth,
+    Color? pathColor,
+    Color? valueColor,
+    bool? roundCap,
   }) {
     //should repaint
     _shouldRepaint = shouldRepaint;
@@ -145,29 +137,35 @@ class StepProgressPainter extends CustomPainter with ProgressMixin {
 
   @override
   bool shouldRepaint(CustomPainter oldDelegate) {
-    return _shouldRepaint;
+    return _shouldRepaint!;
   }
 
   @override
-  drawProgressPath({Canvas canvas, Paint paint, Size size}) {
+  drawProgressPath(
+      {required Canvas canvas, required Paint paint, required Size size}) {
     //draw step progress path
     _drawStep(canvas: canvas, paint: paint, size: size, loopCount: stepCount);
   }
 
   @override
-  drawProgressValue({Canvas canvas, Paint paint, Size size}) {
+  drawProgressValue(
+      {required Canvas canvas, required Paint paint, required Size size}) {
     //draw step progress value
     _drawStep(canvas: canvas, paint: paint, size: size, loopCount: stepValue);
   }
 
-  _drawStep({Canvas canvas, Paint paint, Size size, int loopCount}) {
+  _drawStep(
+      {required Canvas canvas,
+      required Paint paint,
+      required Size size,
+      required int loopCount}) {
     double y = size.height / 2;
 
     double startY = y;
     double endY = y;
     for (int i = 0; i < loopCount; i++) {
-      double startX = i *
-          (_getSingleStepWidth(size: size) + _getSingleSpaceWidth(size: size));
+      double startX =
+          i * (_getSingleStepWidth(size: size) + _getSingleSpaceWidth());
       double endX = startX + _getSingleStepWidth(size: size);
 
       Offset startPoint = Offset(startX, startY);
@@ -181,8 +179,8 @@ class StepProgressPainter extends CustomPainter with ProgressMixin {
     return Paint()
       ..color = pathColor
       ..style = PaintingStyle.stroke
-      ..strokeCap = _roundCap ? StrokeCap.butt : StrokeCap.butt
-      ..strokeJoin = _roundCap ? StrokeJoin.miter : StrokeJoin.miter
+      ..strokeCap = _roundCap! ? StrokeCap.butt : StrokeCap.butt
+      ..strokeJoin = _roundCap! ? StrokeJoin.miter : StrokeJoin.miter
       ..strokeWidth = pathStrokeWidth;
   }
 
@@ -190,27 +188,27 @@ class StepProgressPainter extends CustomPainter with ProgressMixin {
     return Paint()
       ..color = valueColor
       ..style = PaintingStyle.stroke
-      ..strokeCap = _roundCap ? StrokeCap.butt : StrokeCap.butt
-      ..strokeJoin = _roundCap ? StrokeJoin.miter : StrokeJoin.miter
+      ..strokeCap = _roundCap! ? StrokeCap.butt : StrokeCap.butt
+      ..strokeJoin = _roundCap! ? StrokeJoin.miter : StrokeJoin.miter
       ..strokeWidth = valueStrokeWidth;
   }
 
-  int get stepCount => _stepCount;
+  int get stepCount => _stepCount!;
 
-  int get stepValue => _stepValue;
+  int get stepValue => _stepValue!;
 
-  Color get valueColor => _valueColor;
-  Color get pathColor => _pathColor;
+  Color get valueColor => _valueColor!;
+  Color get pathColor => _pathColor!;
 
-  double get pathStrokeWidth => _pathStrokeWidth;
-  double get valueStrokeWidth => _valueStrokeWidth;
+  double get pathStrokeWidth => _pathStrokeWidth!;
+  double get valueStrokeWidth => _valueStrokeWidth!;
 
-  double _getSingleStepWidth({Size size}) {
+  double _getSingleStepWidth({required Size size}) {
     return (size.width - ((stepCount - 1) * _getSingleSpaceWidth())) /
         stepCount;
   }
 
-  double _getSingleSpaceWidth({Size size}) {
-    return _spaceWidth;
+  double _getSingleSpaceWidth() {
+    return _spaceWidth!;
   }
 }
diff --git a/pubspec.lock b/pubspec.lock
index 3107c6e..4079a91 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -1,62 +1,55 @@
 # Generated by pub
 # See https://dart.dev/tools/pub/glossary#lockfile
 packages:
-  archive:
-    dependency: transitive
-    description:
-      name: archive
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "2.0.13"
-  args:
-    dependency: transitive
-    description:
-      name: args
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "1.6.0"
   async:
     dependency: transitive
     description:
       name: async
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "2.4.1"
+    version: "2.6.0"
   boolean_selector:
     dependency: transitive
     description:
       name: boolean_selector
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "2.0.0"
+    version: "2.1.0"
+  characters:
+    dependency: transitive
+    description:
+      name: characters
+      url: "https://pub.flutter-io.cn"
+    source: hosted
+    version: "1.1.0"
   charcode:
     dependency: transitive
     description:
       name: charcode
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.1.3"
-  collection:
+    version: "1.2.0"
+  clock:
     dependency: transitive
     description:
-      name: collection
-      url: "https://pub.dartlang.org"
+      name: clock
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.14.12"
-  convert:
+    version: "1.1.0"
+  collection:
     dependency: transitive
     description:
-      name: convert
-      url: "https://pub.dartlang.org"
+      name: collection
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "2.1.1"
-  crypto:
+    version: "1.15.0"
+  fake_async:
     dependency: transitive
     description:
-      name: crypto
-      url: "https://pub.dartlang.org"
+      name: fake_async
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "2.1.4"
+    version: "1.2.0"
   flutter:
     dependency: "direct main"
     description: flutter
@@ -67,48 +60,27 @@ packages:
     description: flutter
     source: sdk
     version: "0.0.0"
-  image:
-    dependency: transitive
-    description:
-      name: image
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "2.1.12"
   matcher:
     dependency: transitive
     description:
       name: matcher
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "0.12.6"
+    version: "0.12.10"
   meta:
     dependency: transitive
     description:
       name: meta
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.1.8"
+    version: "1.3.0"
   path:
     dependency: transitive
     description:
       name: path
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "1.6.4"
-  petitparser:
-    dependency: transitive
-    description:
-      name: petitparser
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "2.4.0"
-  quiver:
-    dependency: transitive
-    description:
-      name: quiver
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "2.1.3"
+    version: "1.8.0"
   sky_engine:
     dependency: transitive
     description: flutter
@@ -118,64 +90,58 @@ packages:
     dependency: transitive
     description:
       name: source_span
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.7.0"
+    version: "1.8.1"
   stack_trace:
     dependency: transitive
     description:
       name: stack_trace
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.9.3"
+    version: "1.10.0"
   stream_channel:
     dependency: transitive
     description:
       name: stream_channel
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "2.0.0"
+    version: "2.1.0"
   string_scanner:
     dependency: transitive
     description:
       name: string_scanner
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.0.5"
+    version: "1.1.0"
   term_glyph:
     dependency: transitive
     description:
       name: term_glyph
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.1.0"
+    version: "1.2.0"
   test_api:
     dependency: transitive
     description:
       name: test_api
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "0.2.15"
+    version: "0.3.0"
   typed_data:
     dependency: transitive
     description:
       name: typed_data
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.1.6"
+    version: "1.3.0"
   vector_math:
     dependency: transitive
     description:
       name: vector_math
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "2.0.8"
-  xml:
-    dependency: transitive
-    description:
-      name: xml
-      url: "https://pub.dartlang.org"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "3.6.1"
+    version: "2.1.0"
 sdks:
-  dart: ">=2.7.0 <3.0.0"
+  dart: ">=2.13.0 <3.0.0"
+  flutter: ">=1.20.0"
diff --git a/pubspec.yaml b/pubspec.yaml
index b347f49..7676cd6 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,12 +1,12 @@
 name: ai_progress
 description: A new multiple style progress include of circular、linear and step style progress indicator.
-version: 1.0.0
+version: 2.0.0
 homepage: https://pdliuw.github.io/
 repository: https://github.com/pdliuw/ai_progress
 
 environment:
-  sdk: ">=2.7.0 <3.0.0"
-  flutter: ">=1.20.0 <2.0.0"
+  sdk: ">=2.13.0 <3.0.0"
+  flutter: ">=1.20.0"
 
 dependencies:
   flutter:
diff --git a/test/aiprogress_test.dart b/test/aiprogress_test.dart
index 1a49198..2904e9a 100644
--- a/test/aiprogress_test.dart
+++ b/test/aiprogress_test.dart
@@ -1,9 +1,12 @@
+import 'package:flutter/cupertino.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import 'package:ai_progress/ai_progress.dart';
 
 void main() {
   test('adds one to input values', () {
-    AirCircularStateProgressIndicator();
+    AirCircularStateProgressIndicator(
+      size: Size(20, 20),
+    );
   });
 }