💪 Null safety support

example/lib/main.dart

@@ -42,7 +42,7 @@ class Button extends StatelessWidget {
   Widget build(BuildContext context) {
     return Container(
       margin: EdgeInsets.all(4.0),
-      child: RaisedButton(
+      child: ElevatedButton(
         onPressed: function,
         child: Text(
           title,

example/pubspec.lock

@@ -1,69 +1,62 @@
 # 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"
     source: hosted
-    version: "2.4.1"
+    version: "2.6.1"
   boolean_selector:
     dependency: transitive
     description:
       name: boolean_selector
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.0"
-  charcode:
+    version: "2.1.0"
+  characters:
     dependency: transitive
     description:
-      name: charcode
+      name: characters
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.3"
-  collection:
+    version: "1.1.0"
+  charcode:
     dependency: transitive
     description:
-      name: collection
+      name: charcode
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.14.12"
-  convert:
+    version: "1.2.0"
+  clock:
     dependency: transitive
     description:
-      name: convert
+      name: clock
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.1"
-  crypto:
+    version: "1.1.0"
+  collection:
     dependency: transitive
     description:
-      name: crypto
+      name: collection
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.4"
+    version: "1.15.0"
   cupertino_icons:
     dependency: "direct main"
     description:
       name: cupertino_icons
       url: "https://pub.dartlang.org"
     source: hosted
     version: "0.1.3"
+  fake_async:
+    dependency: transitive
+    description:
+      name: fake_async
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.2.0"
   flutter:
     dependency: "direct main"
     description: flutter
@@ -74,62 +67,41 @@ 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"
     source: hosted
-    version: "0.12.6"
+    version: "0.12.10"
   meta:
     dependency: transitive
     description:
       name: meta
       url: "https://pub.dartlang.org"
     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"
+    version: "1.8.0"
   pedantic:
     dependency: transitive
     description:
       name: pedantic
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.9.0"
-  petitparser:
-    dependency: transitive
-    description:
-      name: petitparser
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "2.4.0"
   presentation_displays:
     dependency: "direct main"
     description:
       path: ".."
       relative: true
     source: path
-    version: "0.1.7"
-  quiver:
-    dependency: transitive
-    description:
-      name: quiver
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "2.1.3"
+    version: "0.2.0"
   sky_engine:
     dependency: transitive
     description: flutter
@@ -141,63 +113,56 @@ packages:
       name: source_span
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.7.0"
+    version: "1.8.1"
   stack_trace:
     dependency: transitive
     description:
       name: stack_trace
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.9.3"
+    version: "1.10.0"
   stream_channel:
     dependency: transitive
     description:
       name: stream_channel
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.0"
+    version: "2.1.0"
   string_scanner:
     dependency: transitive
     description:
       name: string_scanner
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.5"
+    version: "1.1.0"
   term_glyph:
     dependency: transitive
     description:
       name: term_glyph
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.0"
+    version: "1.2.0"
   test_api:
     dependency: transitive
     description:
       name: test_api
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.15"
+    version: "0.3.0"
   typed_data:
     dependency: transitive
     description:
       name: typed_data
       url: "https://pub.dartlang.org"
     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"
-    source: hosted
-    version: "3.6.1"
+    version: "2.1.0"
 sdks:
-  dart: ">=2.7.0 <3.0.0"
+  dart: ">=2.12.0 <3.0.0"
   flutter: ">=1.10.0"

lib/display.dart

@@ -110,13 +110,13 @@ class Display {
   /// Each logical display has a unique id.
   /// The default display has id [DEFAULT_DISPLAY]
   /// </p>
-  int displayId = DEFAULT_DISPLAY;
+  int? displayId = DEFAULT_DISPLAY;
 
   /// Returns a combination of flags that describe the capabilities of the display.
   /// @return The display flags.
   ///
   /// See [FLAG_SUPPORTS_PROTECTED_BUFFERS], [FLAG_SECURE], [FLAG_PRIVATE]
-  int flag;
+  int? flag;
 
   /// Returns the rotation of the screen from its "natural" orientation.
   /// The returned value may be [ROTATION_0]
@@ -130,15 +130,15 @@ class Display {
   /// degrees counter-clockwise, to compensate rendering will be rotated by
   /// 90 degrees clockwise and thus the returned value here will be
   /// [ROTATION_90].
-  int rotation;
+  int? rotation;
 
   /// Gets the name of the display.
   /// <p>
   /// Note that some displays may be renamed by the user.
   /// </p>
   ///
   /// @return The display's name.
-  String name;
+  String? name;
 
   Display({this.displayId, this.flag, this.name, this.rotation});
 }

lib/displays_manager.dart

@@ -32,7 +32,7 @@ const String DISPLAY_CATEGORY_PRESENTATION =
 /// Provide you with the method for you to work with [SecondaryDisplay].
 class DisplayManager {
   final _displayChannel = "presentation_displays_plugin";
-  MethodChannel _displayMethodChannel;
+  MethodChannel? _displayMethodChannel;
 
   DisplayManager() {
     _displayMethodChannel = MethodChannel(_displayChannel);
@@ -52,14 +52,14 @@ class DisplayManager {
   /// @return An array containing all displays sorted by order of preference.
   ///
   /// See [DISPLAY_CATEGORY_PRESENTATION]
-  FutureOr<List<Display>> getDisplays({String category}) async {
-    List<dynamic> origins = await jsonDecode(await _displayMethodChannel
-            ?.invokeMethod(_listDisplay, category)) ??
+  Future<List<Display>> getDisplays({String? category}) async {
+    List<dynamic> origins = await jsonDecode((await _displayMethodChannel
+            ?.invokeMethod(_listDisplay, category))) ??
         [];
     List<Display> displays = [];
     origins.forEach((element) {
       Map map = jsonDecode(jsonEncode(element));
-      displays.add(displayFromJson(map));
+      displays.add(displayFromJson(map as Map<String, dynamic>));
     });
     return displays;
   }
@@ -73,10 +73,10 @@ class DisplayManager {
   ///
   /// @return The display's name.
   /// May be null.
-  FutureOr<String> getNameByDisplayId(int displayId, {String category}) async {
-    List<Display> displays = await getDisplays(category: category) ?? [];
+  Future<String?> getNameByDisplayId(int displayId, {String? category}) async {
+    List<Display> displays = await getDisplays(category: category);
 
-    String name;
+    String? name;
     displays.forEach((element) {
       if (element.displayId == displayId) name = element.name;
     });
@@ -92,9 +92,9 @@ class DisplayManager {
   ///
   /// @return The display's name
   /// May be null.
-  FutureOr<String> getNameByIndex(int index, {String category}) async {
-    List<Display> displays = await getDisplays(category: category) ?? [];
-    String name;
+  Future<String?> getNameByIndex(int index, {String? category}) async {
+    List<Display> displays = await getDisplays(category: category);
+    String? name;
     if (index >= 0 && index <= displays.length) name = displays[index].name;
     return name;
   }
@@ -108,8 +108,8 @@ class DisplayManager {
   /// </P>
   ///
   /// return [Future<bool>] about the status has been display or not
-  Future<bool> showSecondaryDisplay(
-      {@required int displayId, @required String routerName}) {
+  Future<bool?>? showSecondaryDisplay(
+      {required int displayId, required String routerName}) {
     return _displayMethodChannel?.invokeMethod(
         _showPresentation,
         "{"
@@ -170,7 +170,7 @@ class DisplayManager {
   /// </p>
   ///
   /// return [Future<bool>] the value to determine whether or not the data has been transferred successfully
-  Future<bool> transferDataToPresentation(dynamic arguments) {
+  Future<bool?>? transferDataToPresentation(dynamic arguments) {
     return _displayMethodChannel?.invokeMethod(
         _transferDataToPresentation, arguments);
   }

lib/secondary_display.dart

@@ -10,21 +10,21 @@ typedef ArgumentsCallback = Function(dynamic arguments);
 /// [SecondaryDisplay.callback] instance of [ArgumentsCallback] to receive data transmitted from the [DisplayManager].
 /// [SecondaryDisplay.child] child widget of secondary display
 class SecondaryDisplay extends StatefulWidget {
-  SecondaryDisplay({@required this.callback, this.child});
+  SecondaryDisplay({required this.callback, this.child});
 
   /// instance of [ArgumentsCallback] to receive data transmitted from the [DisplaysManager].
   final ArgumentsCallback callback;
 
   /// Your Flutter UI on Presentation Screen
-  final Widget child;
+  final Widget? child;
 
   @override
   _SecondaryDisplayState createState() => _SecondaryDisplayState();
 }
 
 class _SecondaryDisplayState extends State<SecondaryDisplay> {
   final _presentationChannel = "presentation_displays_plugin_engine";
-  MethodChannel _presentationMethodChannel;
+  late MethodChannel _presentationMethodChannel;
 
   @override
   void initState() {