blocks|key|16801|text|这里有两种方法来实现这个结果(我没有使用单独的http服务来将所有代码放在一个地方)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|16802|With+to+promise是第一个解决方案，其中im使用来自es5的异步等待函数。我正在创建循环，并在该循环中等待来自循环中的调用的结果，并且只有在此之后才会调用下一个请求。|offset|length|style|BOLD|16803|With+observables第二种解决方案对angularDev更友好，它使用rxjs+Subject，它是在Subject实例上调用.next()方法时发出事件的对象。这里需要注意的是，我们必须在某个时刻取消对主题的订阅，否则将陷入无限循环，这并不酷。还要注意，为了避免未处理的订阅，im使用了first()运算符。|CODE|16804|这是一个现场演示CodeSandbox+*查看控制台|16805|​|16806|import+{+Component+}+from+"@angular/core";
import+{+HttpClient+}+from+"@angular/common/http";

import+{+first+}+from+"rxjs/operators";
import+{+Subject+}+from+"rxjs/Subject";

@Component({
++selector:+"app-root",
++templateUrl:+"./app.component.html",
++styleUrls:+["./app.component.css"]
})
export+class+AppComponent+{
++title+=+"CodeSandbox";

++dumySubject+=+new+Subject();

++constructor(private+http:+HttpClient)+{}

++ngOnInit()+{
++++let+currentIndex+=+1;

++++//With+toPromise
++++let+indexes+=+[1,+2,+3,+4];
++++let+someFunc+=+async+()+=>+{
++++++for+(const+id+of+indexes)+{
++++++++let+someResp+=+this.http
++++++++++.get("https://jsonplaceholder.typicode.com/posts/"+%2B+id)
++++++++++.toPromise()
++++++++++.then(x+=>+{
++++++++++++console.log(x);
++++++++++});
++++++++await+someResp;
++++++++console.log("___");
++++++}
++++};
++++someFunc();

++++//With+observables
++++let+sub+=+this.dumySubject.subscribe(x+=>+{
++++++console.log("in");
++++++if+(currentIndex+>+5)+{
++++++++sub.unsubscribe();
++++++}
++++++this.http
++++++++.get("https://jsonplaceholder.typicode.com/posts/"+%2B+currentIndex)
++++++++.pipe(first())
++++++++.subscribe(x+=>+{
++++++++++console.log(x);
++++++++++console.log("________");
++++++++++currentIndex%2B%2B;
++++++++++this.dumySubject.next();
++++++++});
++++});
++++this.dumySubject.next();

++++console.log("i+m+the+first+line");
++}
}|code-block|syntax|javascript|16807|16808|entityMap|0|LINK|mutability|MUTABLE|url|https://codesandbox.io/s/w07kvp53ol^0|0|0|F|0|0|G|15|4|1A|7|1L|7|1X|7|46|7|0|8|B|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|13|8|@$D|14|E|15|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|16|8|@$D|17|E|18|F|G]|$D|19|E|1A|F|J]|$D|1B|E|1C|F|J]|$D|1D|E|1E|F|J]|$D|1F|E|1G|F|J]|$D|1H|E|1I|F|J]]|9|@]|A|$]]|$1|K|3|L|5|6|7|1J|8|@]|9|@$D|1K|E|1L|1|1M]]|A|$]]|$1|M|3|N|5|6|7|1N|8|@]|9|@]|A|$]]|$1|O|3|P|5|Q|7|1O|8|@]|9|@]|A|$R|S]]|$1|T|3|N|5|6|7|1P|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1Q|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]]]

Here are two ways to achieve the result (im not using separate http service in order to keep all code in one place) 

With to promise is the first solution, in which im using the async await function from es5. Im creating loop and in that loop im awaiting results from the call made in the loop, and only after that the next request is called.

With observables the second solution is more angularDev friendly and is using the <code>rxjs</code> <code>Subject</code> which is such object that emits event upon calling the <code>.next()</code> method over the instance of the <code>Subject</code>. Here is important to notice that we must unsubscribe at some point from the subject, or we will fall in an infinite loop, which is not cool, also notice that im using the <code>first()</code> operator in order to avoid unhanded subscriptions

Here is a live demo <a href="https://codesandbox.io/s/w07kvp53ol" rel="nofollow noreferrer">CodeSandbox</a> *look at the console

<div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>import { Component } from "@angular/core";
import { HttpClient } from "@angular/common/http";

import { first } from "rxjs/operators";
import { Subject } from "rxjs/Subject";

@Component({
 selector: "app-root",
 templateUrl: "./app.component.html",
 styleUrls: ["./app.component.css"]
})
export class AppComponent {
 title = "CodeSandbox";

 dumySubject = new Subject();

 constructor(private http: HttpClient) {}

 ngOnInit() {
 let currentIndex = 1;

 //With toPromise
 let indexes = [1, 2, 3, 4];
 let someFunc = async () =&gt; {
 for (const id of indexes) {
 let someResp = this.http
 .get("https://jsonplaceholder.typicode.com/posts/" + id)
 .toPromise()
 .then(x =&gt; {
 console.log(x);
 });
 await someResp;
 console.log("___");
 }
 };
 someFunc();

 //With observables
 let sub = this.dumySubject.subscribe(x =&gt; {
 console.log("in");
 if (currentIndex &gt; 5) {
 sub.unsubscribe();
 }
 this.http
 .get("https://jsonplaceholder.typicode.com/posts/" + currentIndex)
 .pipe(first())
 .subscribe(x =&gt; {
 console.log(x);
 console.log("________");
 currentIndex++;
 this.dumySubject.next();
 });
 });
 this.dumySubject.next();

 console.log("i m the first line");
 }
}</code></pre>
</div>
</div>

I'm calling a method that is executing some async operations and I want to wait for those methods to be completed before iterating the loop, so that the async operations are done sequentially. But I'm having trouble understanding how this can be achieved. Here is what I'm doing:

<pre><code>_.forEach(this.pendingUsers.queue, (user) =&gt; {
 this.myService.setUserInfo(user);
});
</code></pre>

In the above I would like to add a logic that doesn't increment for loop until setUserInfo() is completed.

NOTE: I'm using Lodash 4's forEach method, so please ignore a different syntax.

Wait for async method to execute before iterating forEach loop: Angular 4

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我正在调用一个正在执行一些异步操作的方法，我希望在迭代循环之前等待这些方法完成，这样异步操作就会按顺序完成。但我很难理解如何才能做到这一点。下面是我正在做的事情：_.forEach(this.pendingUsers.queue, (user) => {  this.myService.setUserInfo(user...

在迭代forEach循环之前等待异步方法执行: Angular 4-腾讯云开发者社区-腾讯云

问在迭代forEach循环之前等待异步方法执行: Angular 4
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