dart

问题 I have newly installed Flutter on Android Studio. I had a source code of flutter which I want to open using it. I installed the latest flutter plugin and flutter SDK. But when I try to run the app, it shows me the following error: Compiler message: /C:/Flutter%20SDK/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_svg-0.14.4/lib/src/picture_stream.dart:92:3: Error: The superclass, 'Diagnosticable', has no unnamed constructor that takes no arguments. PictureStream(); ^^^^^^^^^^^^^ /C:

问题 I have the content of a pdf in base64 and I need to show it in a container in a flutter application. I'm trying to do it with the image, pdf and convert packages from dart,but I get an error with the image class and I don't know how to show the image. List<int> pdfDataBytes = base64.decode(fileContent); Image img = decodeImage(pdfDataBytes); PdfImage image = PdfImage( pdf, image: img.data.buffer.asUint8List(), width: img.width, height: img.height); This is the message of the error in the

问题 I have the content of a pdf in base64 and I need to show it in a container in a flutter application. I'm trying to do it with the image, pdf and convert packages from dart,but I get an error with the image class and I don't know how to show the image. List<int> pdfDataBytes = base64.decode(fileContent); Image img = decodeImage(pdfDataBytes); PdfImage image = PdfImage( pdf, image: img.data.buffer.asUint8List(), width: img.width, height: img.height); This is the message of the error in the

问题 I need to check whether myItemsList contains myitem.itemId or not, If it exists need to add itemQuantity , if it not exists need to add myitem object to myItemsList . List<MyItem> myItemsList = new List(); MyItem myitem = new MyItem ( itemId: id, itemName: name, itemQuantity: qty, ); if (myItemsList.contains(myitem.itemId)) { print('Allready exists!'); } else { print('Added!'); setState(() { myItemsList.add(myitem); }); } MyItem class class MyItem { final String itemId; final String itemName;

问题 I'm trying to parse a binary file in the browser. I have 4 bytes that represent a 32-bit signed integer. Is there a straight forward way of converting this to a dart int, or do I have to calculate the inverse of two's complement manually? Thanks Edit: Using this for manually converting: int readSignedInt() { int value = readUnsignedInt(); if ((value & 0x80000000) > 0) { // This is a negative number. Invert the bits and add 1 value = (~value & 0xFFFFFFFF) + 1; // Add a negative sign value =

问题 I'm building a Flutter app where I would like to keep the data offline. I'm capturing an image using the camera or gallery image picker and able to store that image into a File image variable. File _avatarImg; void _getImage(BuildContext context, ImageSource source) { ImagePicker.pickImage( source: source, maxWidth: 400.0, maxHeight: 400.0, ).then((File image) { _avatarImg = image; }); } This works perfectly however my question is, how would I go about storing this image for persistence?

问题 I'm building a Flutter app where I would like to keep the data offline. I'm capturing an image using the camera or gallery image picker and able to store that image into a File image variable. File _avatarImg; void _getImage(BuildContext context, ImageSource source) { ImagePicker.pickImage( source: source, maxWidth: 400.0, maxHeight: 400.0, ).then((File image) { _avatarImg = image; }); } This works perfectly however my question is, how would I go about storing this image for persistence?

问题 I know that Flutter supports using Skia instead of DomCanvas in Flutter Web using WASM CanvasKit, i.e. "Skia + WebAssembly". I have heard that this provides significant performance improvements, however, I do not know how to enable it. 回答1: You can enable CanvasKit / Skia in Flutter Web by supplying a Dart environment constant: flutter run -d chrome --dart-define=FLUTTER_WEB_USE_SKIA=true The flutter tools now have a good shortcut for it: flutter run -d chrome --web-renderer canvaskit The -

问题 Is there a way to implement GraphQL in flutter? I was trying making the API call with the query and variables objects in a JSON object. type '_InternalLinkedHashMap' is not a subtype of type 'String' in type cast 回答1: I have been using graphql_flutter package for a few weeks now and it seems to work well enough. Here is an example: import 'package:graphql_flutter/graphql_flutter.dart' show Client, InMemoryCache; ... Future<dynamic> post( String body, { Map<String, dynamic> variables, }) async

问题 Is there a way to implement GraphQL in flutter? I was trying making the API call with the query and variables objects in a JSON object. type '_InternalLinkedHashMap' is not a subtype of type 'String' in type cast 回答1: I have been using graphql_flutter package for a few weeks now and it seems to work well enough. Here is an example: import 'package:graphql_flutter/graphql_flutter.dart' show Client, InMemoryCache; ... Future<dynamic> post( String body, { Map<String, dynamic> variables, }) async