dart

问题 Im trying to get an response from provider and fetching in a ui page but when i try to add an response to ui it shows an error The getter 'data' was called on null. Receiver: null Tried calling: data In this Line: ListView.builder( physics: ClampingScrollPhysics(), shrinkWrap: true, itemCount: doctorList.data.length, primary: true, is this is correct approuch or need to change modal class or ui integration. im accessing data through doctorList.data.->datas data. My response modal class.

问题 I am trying to display a list of flutter forms with a list view builder. UI for which I have already done. I want to access the data now for each form and validate, can someone guide me? i tried different approaches and checking similar posts on StackOverflow, but was not able to find any solution for the same. entries_widget.dart - where the form is created class EntriesWidget extends StatefulWidget { EntriesWidget({Key key}) : super(key: key); @override EntriesWidgetState createState() =>

问题 I want to use those basic classes (such as Offset , Size , and Color ), in a pure- dart program. I cannot import them in a pure dart project. How can I use them? Those classes are really fundamental and quite helpful. For example, with Color (and Colors ) the color system can be easily used. So I would appreciate it if I could use them. I have tried this, but it gives me the following error: Error: Not found: 'dart:ui' . I have also tried copying and pasting, but that is a bit ugly... 回答1:

问题 I have a flutter app using Firebase's cloud firestore. I've done the web build and running it on Chrome through Android Studio works well. I would like to share my web app progress to my client but don't want to host it (because it's not finished yet). Hence I'd like to find a way to run it locally the same way you can do it with Android Studio but without needing to install Android Studio (and hopefully not requiring to install flutter either), so that I can send the build file to my client

问题 Till yesterday, VSCode was running fine, but after dart updated itself, VSCode has stopped recognizing my code as a language. When I type CTRL+F5, it pops up asking to select a compiler. The code runs fine, but it is not able to recognize it. Side note, it works in Android Studio. Updating the pubspec.yaml file just removes errors but the code is still not recognized. Popup: https://i.stack.imgur.com/c2WZR.png No syntax highlighting/nothing: https://i.stack.imgur.com/EmtiU.png P.S: It

问题 I want to confirm exiting the app when the back button on the appbar is pressed. appBar: AppBar( leading: IconButton( icon: Icon( Icons.arrow_back_ios, color: Colors.white, ), onPressed: () { showDialog( context: context, builder: (context) { return AlertDialog( title: Text('Save and Exit?'), content: Text('are you sure you want to save and exit?'), actions: [ FlatButton( onPressed: () => Navigator.pop(context, false), child: Text('No'), ), FlatButton( onPressed: () => Navigator.pop(context,

问题 Like in this example: https://github.com/brianegan/github_search_angular_flutter/blob/master/github_search_common/lib/src/ui/search_state.dart The class is referenced to without the dollar sign in other parts of the code. I couldn't find any documentation about this. 回答1: $ is a valid character for any name in Dart. In this case, it looks like the convention for https://pub.dartlang.org/packages/meta_types I'd look at that documentation. 来源： https://stackoverflow.com/questions/52729086/is

问题 I am loading some text from a file in a String variable in my code. This text has certain values that must be filled-in dynamically from a Map. When I use a String directly in my code, it works fine as desired. But when the same string is loaded from the file, it does not perform the required string interpolation. Consider this for string interpolation - String parseText(Map<String, dynamic> ctx){ return "My name is ${ctx['employee'].name} and I joined today, ${ctx['today']}"; } This works

问题 I need the ability to start two processes from dart, read the input from the first process, manipulate the output in dart and then send the data to a second process. Note: in this example I state two processes but in reality I may need to create a pipe line involving any number of processes. The two process are likely to be long running (assume minutes) and the output must be available as the processes process the data (think tail -f). To re-inforce the last point the process may output large

问题 I need the ability to start two processes from dart, read the input from the first process, manipulate the output in dart and then send the data to a second process. Note: in this example I state two processes but in reality I may need to create a pipe line involving any number of processes. The two process are likely to be long running (assume minutes) and the output must be available as the processes process the data (think tail -f). To re-inforce the last point the process may output large