带有switchMap的角度获取路由参数不起作用[重复]

Question

我正在尝试按照Angular Routing 文档中有关如何获取路由参数的教程进行操作。

使用subscribe时可以获取路由参数。

this.getRouteParams$ = this.route.params.subscribe(params => {
  // Works
  console.log(params);
});

但是根据文档，最好使用 switchMap。我无法让 switchMap 示例在我的代码中工作，我不知道为什么。

import { switchMap } from 'rxjs/operators';

this.getRouteParams$ = this.route.params.pipe(
  switchMap(params => {
    // Does not work
    console.log(params);
    // How to check params here and then subscribe to other observables conditionally
  })
);

最终目的是在收到并验证后，使用switchMap根据路由参数的值有条件地调用其他observable。但是，我什至无法让第一个 switchMap 语句正常工作，如上所示。

Answer 1

您需要订阅以评估 Observable 并根据参数有条件地调用另一个 observable，这样做：

import { switchMap } from 'rxjs/operators';

this.getRouteParams$ = this.route.params.pipe(
  switchMap(params => {
    console.log(params);
    // How to check params here and then subscribe to other observables conditionally
    //here you can check the params and return the another observable like this:

    //BELOW code is just to show how to return another observable conditionally
    //Change it as per your logic
    const p = params['id']; //i am assuming that your param name is `id`; 
    if(p === 100) {
       return this.anotherObservable()
                  .pipe(
                     tap(r => {
                       //DO whaterver you want to do with the response of the observable
                       console.log(r);
                     })
                   );
    } else {
       return of(someThingAsPerYourLogic);
    }
  })
).subscribe();

Answer 2

//this will work
import { switchMap } from 'rxjs/operators';

this.getRouteParams$ = this.route.params.pipe(
  switchMap(params => {
    // Does not work
    console.log(params);
    // How to check params here and then subscribe to other observables conditionally
  })
).subscribe(item=>{
console.log(item
})