如何解决Flutter:Dart Cast Error空值检查运算符用于空值
我是 Flutter 的新手,我正在尝试打开相机,为此我遵循了示例代码,但是每当我调试我的应用程序时,它都会给我异常,如图
这是我的代码:
import 'dart:async';
import 'package:Flutter/material.dart';
import 'package:camera/camera.dart';
import 'home.dart';
List<CameraDescription> cameras;
Future<Null> main() async {
try {
cameras = await availableCameras();
} on CameraException catch (e) {
print('Error: $e.code\nError Message: $e.message');
}
runApp(new MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,title: 'RealTime Detection',home: HomePage(cameras),);
}
}
解决方法
你可以这样做:
let words = "is2 Thi1s T4est 3a";
let wordsArr = words.split(" ");
let result = [];
let r = /\d+/g;
outerLoop: // this is a "label" which we can use to reference this for loop
for (let i = 1; i <= wordsArr.length; i++) { // loop 1 to 4,same as the numbers in text
innerLoop:
for (let word of wordsArr) { // for each word
let match = word.match(r); // get the match result
if (match && match[0] == i) { // if match found,and the part that matches is our next i
result.push(word); // add word to array
continue outerLoop; // go to next i
}
}
}
console.log(result.join(" "));
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