[英]In a Dart async method, can certain lines that don't share any dependencies be run asynchronously?
假设您有一个异步方法主体(如下所示),该方法主体具有一个返回Future的方法调用,并在其后打印不需要该方法结果的输出。 是否可以添加一些结构来使打印语句独立执行? 还是这个语法糖迫使异步方法主体按顺序完全运行?
Future<String> test2() {
Completer c = new Completer();
new Timer(new Duration(seconds: 2), () {
c.complete('test2: done');
});
return c.future;
}
Future<String> test1() async {
String result = await test2();
print(result);
// Why is this not executed immediately before test2 call completes?
print('hello');
return 'test1: done';
}
void main() {
test1().then((result) => print(result));
}
后续:我在下面添加了对test1()的重写,该重写已链接了异步方法调用。 我真的很想知道如何使用异步语法糖来简化这种用例。 如何使用新语法重写该块?
Future<String> test1() async {
test2().then((result) {
print(result);
test2().then((result) {
print(result);
});
});
// This should be executed immediately before
// the test2() chain completes.
print('hello');
return 'test1: done';
}
编辑以跟进:
我不确定您到底要做什么,但是如果要在打印之前等待链完成,则必须执行以下操作:
Future<String> test1() async {
String result;
var result1 = await test2();
print("Printing result1 $result1 ; this will wait for the first call to test2() to finish to print");
var result2 = await test2();
print("Printing result2 $result2 ; this will wait for the second call to test2() to print");
// This should be executed immediately before
// the test2() chain completes.
print('hello');
return 'test1: done';
}
现在,如果调用test1()
并等待其返回“ test1:done”,则必须等待它。
main() async {
var result = await test1();
print(result); // should print "hello" and "test1: done"
}
如果要独立于先前的将来结果执行代码,请不要放入await
关键字。
Future<String> test1() async {
test2().then((String result) => print(result)); // the call to test2 will not stop the flow of test1(). Once test2's execution will be finished, it'll print the result asynchronously
// This will be printed without having to wait for test2 to finish.
print('hello');
return 'test1: done';
}
关键字await
使流程停止,直到test2()
完成。
这是因为在test2();
之前await
test2();
。 执行将暂停,直到test2()
返回的Future完成。
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