Angular - Make multiple HTTP calls sequentially

问题:

I need to make a function to make HTTP calls sequentially inorder to use response of one call into other one like getting IP address of user from first call and use that IP to register user in second call.

Demo code:

registerUser(user: User) {
    this.utility.getIpAddress()
    .subscribe(data => {
        this.ipAddress = data.ip;
    });
    const body = {
        UserName: user.UserName,
        Email: user.Email,
        //...
        UserIP: this.ipAddress,
    }
    return this.http.post(this.registerAPI, body);
}

回答1:

This can be achieved using the switchMap operator. This example uses RxJS 5.5+ pipeable operators.

import { switchMap } from 'rxjs/operators';

registerUser(user: User) {
  return this.utility.getIpAddress().pipe(
    switchMap(data => {
      this.ipAddress = data.ip;

      const body = {
        UserName: user.UserName,
        Email: user.Email,
        UserIP: this.ipAddress,
      };

      return this.http.post(this.registerAPI, body);
    })
  )
}

RxJS < 5.5:

import { switchMap } from 'rxjs/operators';

registerUser(user: User) {
  return this.utility.getIpAddress()
    .switchMap(data => {
      this.ipAddress = data.ip;

      const body = {
        UserName: user.UserName,
        Email: user.Email,
        UserIP: this.ipAddress,
      };

      return this.http.post(this.registerAPI, body);
    });
}

Hopefully that helps!