Dart绝大多数的操作符和其他语言很相似，先列一张表
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下面说一些不常见的
- as 强转操作符
(emp as Person).firstName = 'Bob';
- is / is! 判断对象类型操作符
if (emp is Person) {
// Type check
emp.firstName = 'Bob';
}else if(emp is! Person){
.....
}
- 空赋值操作符
b ??= value; //当b为空的时候，value的值才会赋值给b
?. 类似于Kotlin的非空判断，a?.b 在a不为空的时候执行a.b
for in循环，除了常规的for循环以外，还支持for in 循环
var collection = [0, 1, 2];
for (var x in collection) {
print(x); // 0 1 2
}
- Switch case 除了正常的比较也是支持枚举类型的
var command = 'OPEN';
switch (command) {
case 'OPEN':
executeOpen();
// ERROR: Missing break
case 'CLOSED':
executeClosed();
break;
}
还有一种用法是在进入一个case之后根据判断如果true我要执行A case 如果是false我要执行 B case，Dart也提供了支持，利用continue关键字加上自定义的标签来完成
var command = 'CLOSED';
switch (command) {
case 'CLOSED':
executeClosed();
continue nowClosed;
// Continues executing at the nowClosed label.
nowClosed:
case 'NOW_CLOSED':
// Runs for both CLOSED and NOW_CLOSED.
executeNowClosed();
break;
}
断言
Dart里面支持断言，你必须确保判断是正确的才能通过这个断言，断言在生产环境中不起作用
// Make sure the variable has a non-null value.
assert(text != null);
// Make sure the value is less than 100.
assert(number < 100);
// Make sure this is an https URL.
assert(urlString.startsWith('https'));
异常
throw Exception
void distanceTo(Point other) => throw UnimplementedError();//这是抛出异常的方法catch
try {
breedMoreLlamas();
} on OutOfLlamasException {
// A specific exception
buyMoreLlamas();
} on Exception catch (e) {
// Anything else that is an exception
print('Unknown exception: $e');
} catch (e) {
// No specified type, handles all
print('Something really unknown: $e');
}
on和catch的区别应该在于是否关心异常的实例
- 捕获堆栈信息
try {
// ···
} on Exception catch (e) {
print('Exception details:\n $e');
} catch (e, s) {
print('Exception details:\n $e');
print('Stack trace:\n $s');
}
你可以在catch里面多增加一个参数，第一个是异常的实例，第二个则是错误的堆栈信息
- rethrow
Dart允许你在捕获异常的同时进行传播，如果你需要这样做，请使用rethrow关键字
void misbehave() {
try {
dynamic foo = true;
print(foo++); // Runtime error
} catch (e) {
print('misbehave() partially handled ${e.runtimeType}.');
rethrow; // Allow callers to see the exception.
}
}
void main() {
try {
misbehave();
} catch (e) {
print('main() finished handling ${e.runtimeType}.');
}
}
By the way .Dart does support "Finally" keyWord too.
