dart

问题 With NNBD, you're not allowed to initialise the list using the default constructor: List<int> foo = List(); // Compile time error However, you can still do: List<int> foo = []; // No error So, what's the difference between the two? Either both of them should show the error or none of them. 回答1: The List constructor had two uses: new List() to create an empty growable list, equivalent to [] . new List(n) to create a fixed-length list of length n filled with null values With null safety, the

问题 I'm just trying to run the first app and this is what happens: FAILURE: Build failed with an exception. What went wrong: A problem was found with the configuration of task ':app:processDebugResources'. File 'C:\Users\XXXX\Appdata\Local\Android\sdk\platforms\android-28\android.jar' specified for property 'androidJar' does not exist. Try: Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights. Get more

问题 I set everything up as shown in the example project: import 'package:get_it/get_it.dart'; import 'package:places/services/authService.dart'; final locator = GetIt.instance; void setupLocator() { locator.registerSingleton<AuthService>(AuthService()); print("registered"); } with the call in the main file void main() { setupLocator(); runApp(MyApp()); } I have some Check where the locator also correctly return my AuthService class AuthGuardView extends StatefulWidget { AuthGuardView({Key key}) :

问题 I implemented the WidgetsBindingObserver , but the app is NEVER sent to the background so it doesn't recognize the AppLifecycleState.resumed this is the current implementation @override void didChangeAppLifecycleState(AppLifecycleState state) async { print('\n\ndidChangeAppLifecycleState'); switch (state) { case AppLifecycleState.resumed: print('\n\nresumed'); _mymethod(); break; case AppLifecycleState.inactive: print('\n\ninactive'); break; case AppLifecycleState.paused: print('\n\npaused');

问题 This question already has answers here : flutter ListView scroll to index not available (5 answers) Closed 8 months ago . I am creating a website with Flutter Web, and I want to navigate down in the screen with onTap on top Navbar. Like we do it in web development which will navigate to a specific id. How can I achieve this? Can we use ScrollController? EDIT: I found the solution here: https://stackoverflow.com/a/58924800/11545939 回答1: You should use ScrollController like this: EDIT var

问题 So I got this painter to draw a minimap for my game: class MiniMapPainter extends CustomPainter { final GameMap map; final double tileSize; final List<ui.Image> images; MiniMapPainter( {@required this.images, @required this.map, @required this.tileSize}); @override void paint(Canvas canvas, Size size) { var row = 0; var column = 0; map.encodedMap.runes.forEach((charCode) { final character = String.fromCharCode(charCode); if (character == map.rowSeparator) { row++; column = 0; } else if

问题 The Json response has encrypted objects which has to be decrypted to get the actual process. In android GZip was used .How can I achieve this The sample Json is as mentioned below.Any help is really appreciated. { "Data": "1.´ABCD´1150275,11028´01-Jan-2021´8,000.00´", "Data": [ { "Element": "8iMAAB+LCAAAAAAABADt1T8zBxwHgkefKcGh98Zcdz8FSqj9DMzK4d+L0Nj1tveNR2w6M8rRs3PJWBFDy" }, { "Element": "B1AV4bGp6JzQJI8ChnxzixrlT8vKnYHPwRM8zykKVn2gkceAFdxMwU0to" } ], "Status": 1, "Msg": "Success",

问题 I am working on flutter application where i have to show time stamps but the response i got from api is in 24 hr format and i want to display time in 12 hr format in my application. And i want to display on application in this format Can you please help me regarding the easiest way of doing the formatting from 24 hr to 12 hr? 回答1: Dart intl framework helps you to format date/time into any type you want. https://pub.dev/packages/intl Especially for your case, you can use this code. DateFormat(

问题 Excuse the ignorance i am new to Flutter. I am practicing on a course I did and I have the following scenario: I have a view where I consume a web service in the method getDataArray ( FutureBuilder ), and I just want it to be done only once when this view is accessed. I also have a TextField , FutureBuilder and the TextField is in the build() . My widget is a StatefulWidget because it needs to be redrawn to show the character counter of my TextField , so I think this is the reason that every

问题 My code is pretty simple: typedef GenericCallback = void Function<T>(T); void main() { GenericCallback callback = <String>(String message) => printMessage(message); } void printMessage([String errorMessageReason]) { print(errorMessageReason ?? ''); } And DartPad gives me this error at the word message in printMessage(message) : Error: The argument type 'String/*1*/' can't be assigned to the parameter type 'String/*2*/'. - 'String/*1*/' is from 'unknown'. - 'String/*2*/' is from 'dart:core'.