dart

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 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 the following Collection / Documents Location Collection { "geoHash" : "wwscjrm3nu01", "timeStamp" : "March 25, 2020 at 1:07:38 PM UTC-4" } { "geoHash" : "wwscjrm2wc2h", "timeStamp" : "March 25, 2020 at 2:07:38 PM UTC-4" } please replace the GeoHashs# with the example above So, I was trying to query a range of those GeoHashs with ordering them by timestamp "DESC", Like the following db.collection('location') .where('geoHash', '>=', 'wwkxt4kxmmvk') .where('geoHash', '<=', 'wwt4vsn22peq'

问题 I have the following Collection / Documents Location Collection { "geoHash" : "wwscjrm3nu01", "timeStamp" : "March 25, 2020 at 1:07:38 PM UTC-4" } { "geoHash" : "wwscjrm2wc2h", "timeStamp" : "March 25, 2020 at 2:07:38 PM UTC-4" } please replace the GeoHashs# with the example above So, I was trying to query a range of those GeoHashs with ordering them by timestamp "DESC", Like the following db.collection('location') .where('geoHash', '>=', 'wwkxt4kxmmvk') .where('geoHash', '<=', 'wwt4vsn22peq'

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 Developing with ruby on rails allowed to do things like : File.any_instance.expects(:delete) This was a great way to test for side effects within a method call. How to do the equivalent in dart? For example if you have in dart : class Storage { // the function to test void deleteFile(String path) { var fileToDelete = new File(path); if (await fileToDelete.exists()) { await fileToDelete.delete(); } } } ... test("#deleteFile delete the file exists", () { storage = new Storage(); // something

问题 I have a Firestore collection called 'Feeds' that contains a list of posts for a given user's feed (like Instagram). When the view loads, I call a future and order by time var userPostsDocumentSnapshot = await _feeds .document(userUid) .collection(items) .orderBy('postDateTime', descending: true) .getDocuments(); I was initially using a stream, but when new data is added to the user's feed, I don't want it to show automatically, I want a pull-down-to-load new data. However, I also want to

问题 I have the following, which works for int s: extension IterableInt on Iterable<int> { int get max => reduce(math.max); int get min => reduce(math.min); int get sum => reduce((a, b) => a + b); } I wanted to make this more general to include decimals and created this: extension IterableNum on Iterable<num> { num get max => reduce(math.max); num get min => reduce(math.min); num get sum => reduce((a, b) => a + b); } These mostly fail, using the following tests: void main(List<String> args) {

问题 I have a DateTime and I'm trying to do two things with it. 1: Only update the date and month. 2: Only update the time. How can I achieve that? DateTime currentDateTime = DateTime.now(); void updateTime(DateTime newTime) { currentDateTime = ? } void updateDate(DateTime newTime) { currentDateTime = ? } Is there any way I can destruct the currentDateTime like DateTime(...currentDateTime, ..newTime) 回答1: Construct your Datetime object from Datetime.now() properties, instead of the whole Datetime