Flutter

问题 ════════ Exception caught by widgets library ═══════════════════════════════════ The following assertion was thrown building HomePage(dirty, state: _HomePageState#493d9): Assertion failed: F:\…\painting_network_image_web.dart:23 url != null is not true This is the error I get when I add this codes in home.dart WallpaperModel wallpaperModel = WallpaperModel(); wallpaperModel = WallpaperModel.fromMap(element); wallpapers.add(wallpaperModel); also /widget/widget.dart Widget wallpapersList({List

问题 ════════ Exception caught by widgets library ═══════════════════════════════════ The following assertion was thrown building HomePage(dirty, state: _HomePageState#493d9): Assertion failed: F:\…\painting_network_image_web.dart:23 url != null is not true This is the error I get when I add this codes in home.dart WallpaperModel wallpaperModel = WallpaperModel(); wallpaperModel = WallpaperModel.fromMap(element); wallpapers.add(wallpaperModel); also /widget/widget.dart Widget wallpapersList({List

问题 ════════ Exception caught by widgets library ═══════════════════════════════════ The following assertion was thrown building HomePage(dirty, state: _HomePageState#493d9): Assertion failed: F:\…\painting_network_image_web.dart:23 url != null is not true This is the error I get when I add this codes in home.dart WallpaperModel wallpaperModel = WallpaperModel(); wallpaperModel = WallpaperModel.fromMap(element); wallpapers.add(wallpaperModel); also /widget/widget.dart Widget wallpapersList({List

问题 ════════ Exception caught by widgets library ═══════════════════════════════════ The following assertion was thrown building HomePage(dirty, state: _HomePageState#493d9): Assertion failed: F:\…\painting_network_image_web.dart:23 url != null is not true This is the error I get when I add this codes in home.dart WallpaperModel wallpaperModel = WallpaperModel(); wallpaperModel = WallpaperModel.fromMap(element); wallpapers.add(wallpaperModel); also /widget/widget.dart Widget wallpapersList({List

问题 Currently, I have enabled 'keep logging in' function if the user log in once successfully. However, I still want to make a 'remember me' checkbox to save the success login information for user. Can anyone please help me with this? Need: a checkbox that enables the user to store email and password if the user logged in once successfully. Code is shown below: signIn(String email, pass) async { SharedPreferences sharedPreferences = await SharedPreferences.getInstance(); String url =

问题 I have an app uploading joystick position data to a webserver using an API call. This method gets called when a joystick is moved. It stops any previously running isolate and starts a new isolate if the joystick is not in the centre. void onJoystickMoved(double angle, double distance) { stopIsolate(); if(distance > 0.06){ startIsolate(JoystickPosition.fromDistanceAndRadius(distance, angle)); } } The isolate start and stop methods Future<void> startIsolate(JoystickPosition position) async {

问题 I have this action Future<void> signUpAction(Store<AppState> store) async { try { // ... } catch (e) { // .. } } And I dispatch it like this store.dispatch(signUpAction); Now, if I want to pass two paramters, how would I do that? Since there is already one parameter there. I tried this Future<void> signUpAction(Store<AppState> store, email, password) async { try { // ... } catch (e) { // .. } } but then on dispatching, if I do store.dispatch(signUpAction("some@email.com", "somEPa55word!"));

问题 In my flutter app, I have a ConnectivityStatus widget which displays the current connection status of the app to my raspberry pi. In the initState of my widget, I subscribe to a timer to check the connection every 5 seconds and update the state accordingly, then unsubscribe upon disposal. The issue is, when multiple screens use the ConnectivityStatus widget, such as in a stack navigator setup, I now have two concurrent subscriptions as neither instance has disposed. This causes many redundant

问题 I have a probleme with flutter. I install Android Studio and configure that for flutter (install flutter and Dart) but I can't run my app on any device and android studio console returned: Unable to locate a development device; please run 'flutter doctor' for information about installing additional components. and flutter doctor -v : [✓] Flutter (Channel beta, v0.8.2, on Linux, locale en_US.UTF-8) • Flutter version 0.8.2 at /home/mostafa/Dev/Flutter/flutter • Framework revision 5ab9e70727 (4

问题 I'm trying to make a loyalty app by QR scan and unsure how I can get the string value of the QR code generated to each user and then store it in firebase so that it links to a specific user then update the number of times the user's QR code has been scanned in a sub-collection linked to the user collection. QrImage( data: '${user?.uid}', version: QrVersions.auto, size: 300, errorStateBuilder: (cxt, err) { return Container( child: Center( child: Text('Error', textAlign: TextAlign.center, style