Short answer: Instead of the pre-null-safety operations var foo = List<int>(); // Now error var bar = List<int>(n); // Now error var baz = List<int>(0); // Now error use the following: var foo = <int>[]; // Always the recommended way. var bar = List.filled(1, 0); // Not filled with `null`s. var baz = List<int>.empty(); Long … Read more
Dart constructs objects in two phases: first outside-in and then inside-out. Initializer lists are executed outside-in (from derived class to base class). After this is done, the object’s members should be initialized, the object is considered to be “constructed”, and this exists. (That’s why you can’t use this in a meaningful way in an initializer … Read more
Update Flutter 2.0 (Recommended): On latest Flutter version, you should use: AppBar( systemOverlayStyle: SystemUiOverlayStyle( // Status bar color statusBarColor: Colors.red, // Status bar brightness (optional) statusBarIconBrightness: Brightness.dark, // For Android (dark icons) statusBarBrightness: Brightness.light, // For iOS (dark icons) ), ) Only Android (more flexibility): import ‘package:flutter/services.dart’; void main() { SystemChrome.setSystemUIOverlayStyle(SystemUiOverlayStyle( systemNavigationBarColor: Colors.blue, // navigation … Read more
You could use https://github.com/slightfoot/flutter_after_layout which executes a function only one time after the layout is completed. Or just look at its implementation and add it to your code 🙂 Which is basically void initState() { super.initState(); WidgetsBinding.instance .addPostFrameCallback((_) => yourFunction(context)); }
Dart does not allow field initializers to refer to the object itself. Fields must always be fully initialized before any access is given to the object begin created. The initializers can only access static and top-level variables, not any instance variables on the object itself. With null safety, you will be allowed to write late … Read more
Thanks to Dart’s factory constructors, it’s easy to build a singleton: class Singleton { static final Singleton _singleton = Singleton._internal(); factory Singleton() { return _singleton; } Singleton._internal(); } You can construct it like this main() { var s1 = Singleton(); var s2 = Singleton(); print(identical(s1, s2)); // true print(s1 == s2); // true }
This answer will cover both passing data forward and passing data back. Unlike Android Activities and iOS ViewControllers, different screens in Flutter are just widgets. Navigating between them involves creating something called a route and using the Navigator to push and pop the routes on and off the stack. Passing data forward to the next … Read more
You can use the intl package (installer) to format dates. For en_US formats, it’s quite simple: import ‘package:intl/intl.dart’; main() { final DateTime now = DateTime.now(); final DateFormat formatter = DateFormat(‘yyyy-MM-dd’); final String formatted = formatter.format(now); print(formatted); // something like 2013-04-20 } There are many options for formatting. From the docs: ICU Name Skeleton ——– ——– … Read more
There is a post on dart’s website and it explains it pretty well. Final: “final” means single-assignment: a final variable or field must have an initializer. Once assigned a value, a final variable’s value cannot be changed. final modifies variables. Const: “const” has a meaning that’s a bit more complex and subtle in Dart. const … Read more
index.html <head> <!– <link rel=”import” href=”https://stackoverflow.com/questions/20982489/packages/polymer/polymer.html”> not necessary anymore (only in elements)–> <!– <script src=”packages/web_components/platform.js”></script> not necessary anymore with Polymer >= 0.14.0 –> <!– <script src=”packages/web_components/dart_support.js”></script> not necessary anymore with Polymer >= 0.15.0 –> <!– old –> <script type=”application/dart”> export ‘package:polymer/init.dart’;</script> <!– new –> <script type=”application/dart”>export ‘index.dart’;</script> </head> <body> … <!– … when you use … Read more