dart

问题 I need to query fields and get all sub-collections and fields. Is it possible? Stream<List<ChatFieldModel>> getChatField(String uid) { var ref = _db.collection('chats') .where('toUserId', isEqualTo: uid); //Afterthat need to get sub collection with sub collection list of documents and main collection fields value. is it possible? return ref.snapshots().map((list) => list.documents .map((doc) => ChatFieldModel.fromForestore(doc)) .toList()); } 回答1: Firestore queries are shallow. They only

问题 I need to query fields and get all sub-collections and fields. Is it possible? Stream<List<ChatFieldModel>> getChatField(String uid) { var ref = _db.collection('chats') .where('toUserId', isEqualTo: uid); //Afterthat need to get sub collection with sub collection list of documents and main collection fields value. is it possible? return ref.snapshots().map((list) => list.documents .map((doc) => ChatFieldModel.fromForestore(doc)) .toList()); } 回答1: Firestore queries are shallow. They only

问题 There are a number of sync and async operations for files in dart:io: file.deleteSync() and file.delete() file.readAsStringSync() and file.readAsString() file.writeAsBytesSync(bytes) and file.writeAsBytes(bytes) and many, many more. What are the considerations that I should keep in mind when choosing between the sync and async options? I seem to recall seeing somewhere that the sync option is faster if you have to wait for it to finish anyway ( await file.delete() for example). But I can't

问题 I want to use the Stripe library on the web flutter. But unfortunately, until now there is still no stripe library available for web flutter. Therefore I try to run javascript on the web flutter, where it will call the stripe-js library (https://stripe.com/docs/js/payment_intents/confirm_card_payment). What I want to ask, first, is how to use the javascript library on web flutter? like this : <script src = "https://js.stripe.com/v3/"> </script> Secondly, how do I call the javascript function

问题 I'm currently learning Dart, but this is also applicable to what's going on in the JavaScript world right now, and it seems like C# also uses the same pattern. In Dart, any function that uses await must itself be labeled asynchronous through async as follows: import "dart:html"; main() async { var context = querySelector("canvas").context2D; var running = true; while (running) { var time = await window.animationFrame; ... } } This does not make sense to me. If a function is waiting on an

问题 I'm currently learning Dart, but this is also applicable to what's going on in the JavaScript world right now, and it seems like C# also uses the same pattern. In Dart, any function that uses await must itself be labeled asynchronous through async as follows: import "dart:html"; main() async { var context = querySelector("canvas").context2D; var running = true; while (running) { var time = await window.animationFrame; ... } } This does not make sense to me. If a function is waiting on an

问题 I'm trying to use the IconButton that can open the drawer on my app page, so when I tap the icon button, I expect to see the drawer. I've been looking up a way to do so online, but seemed like there're only two solutions: I can either use the appbar to put the IconButton in, or I can try the floating action button. But they're not what I'm looking for, I want just the IconButton to open the drawer. Is it possible do it? 回答1: Yes, you can easily open the drawer through IconButton without using

问题 I'm doing ZigZag encoding on 32bit integers with Dart. This is the source code that I'm using: int _encodeZigZag(int instance) => (instance << 1) ^ (instance >> 31); int _decodeZigZag(int instance) => (instance >> 1) ^ (-(instance & 1)); The code works as expected in the DartVM. But in dart2js the _decodeZigZag function is returning invalid results if I input negativ numbers. For example -10 . -10 is encoded to 19 and should be decoded back to -10 , but it is decoded to 4294967286 . If I run

问题 I'm doing ZigZag encoding on 32bit integers with Dart. This is the source code that I'm using: int _encodeZigZag(int instance) => (instance << 1) ^ (instance >> 31); int _decodeZigZag(int instance) => (instance >> 1) ^ (-(instance & 1)); The code works as expected in the DartVM. But in dart2js the _decodeZigZag function is returning invalid results if I input negativ numbers. For example -10 . -10 is encoded to 19 and should be decoded back to -10 , but it is decoded to 4294967286 . If I run

问题 I designed a web app using the Flutter web. I hosted it with Firebase host. But It's not showing changes of my code after deploying to firebase. It's still showing my older version of web app. But I can overcome this problem by clearing cache memory of browser or ctrl+refresh . But I don't want to do this every time I deploy to firebase. How to stop saving my web app in cache memory? hosted link: https://frcovid19dashboard.web.app 回答1: Append a version number to your main.dart file. Every