Question

我试图进行后端调用以获取一些数据并从中进行第二次调用。后端调用完美，但唯一的问题是承诺。我无法从第一个承诺获得数据，所以我可以从它进行第二次调用.. 我做错了什么想法？

login() {
        if (this.formLogin.valid) {
            var data;
            this.userService.performRequestLoginToBackend(this.formLogin.value.username, this.formLogin.value.password).then(response => {
               data = response;
                //    this.userStore.dispatch({type: 'USER_LOGIN', data: this.userData});
            }, (response) => {
                if (response.status < 500) {
                    console.warn('Login failed!');
                } else {
                    console.error('Internal Server Error');
                }
            });
             this.userService.performSecondRequestLogin(data).then(response2 => {

                    this.parsePromise(response2);
                }, (response2) => {
                    if (response2.status < 500) {
                        console.warn('Login failed!');
                    } else {
                        console.error('Internal Server Error');
                    }
                });
        }
    }

我试过的第二种方式：

login() {
        if (this.formLogin.valid) {

            this.userService.performRequestLoginToBackend(this.formLogin.value.username, this.formLogin.value.password).then(response => {
              this.userService.performSecondRequestLogin(response).then(response2 => {

                    this.parsePromise(response2);

                }, (response2) => {
                    if (response2.status < 500) {
                        console.warn('Login failed!');
                    } else {
                        console.error('Internal Server Error');
                    }
                });
                //    this.userStore.dispatch({type: 'USER_LOGIN', data: this.userData});
            }, (response) => {
                if (response.status < 500) {
                    console.warn('Login failed!');
                } else {
                    console.error('Internal Server Error');
                }
            });

        }
    }

更新：仍然无法运作......

  login() {
        if (this.formLogin.valid) {

            this.userService.performRequestLoginToBackend(this.formLogin.value.username, this.formLogin.value.password).then(response => {
                 return this.userService.performSecondRequestLogin(response);
                //    this.userStore.dispatch({type: 'USER_LOGIN', data: this.userData});
            }, (response) => {
                if (response.status < 500) {
                    console.warn('Login failed!');
                } else {
                    console.error('Internal Server Error');
                }
            }).then(response => {

                  this.parsePromise(response);

            },(response) => {
                if (response.status < 500) {
                    console.warn('Login failed!');
                } else {
                    console.error('Internal Server Error');
                }
            });
        }
    }

后端呼叫第一次呼叫

     performRequestLoginToBackend(_username: string, _password: string) {

    let promise = new Promise((resolve, reject) => {
      this.http.get('xxx').subscribe(data => {
      });

    });
    return promise;
  }

Answer 1

您可以使用以下链接承诺。在这种情况下，最后的then回调，响应是第二次调用的响应。

this.userService.performRequestLoginToBackend(
  this.formLogin.value.username,
  this.formLogin.value.password).then(response => {
           data = response;
          return this.userService.performSecondRequestLogin(data); // <-----
        }, (response) => {
            if (response.status < 500) {
                console.warn('Login failed!');
            } else {
                console.error('Internal Server Error');
            }
        }).then(response => {
          (...)
        });

Answer 2

我认为@Thierry Templier的答案几乎就在那里，但你需要正确地平衡承诺链：

this.userService.performRequestLoginToBackend(
      this.formLogin.value.username,
      this.formLogin.value.password).then((response) => {

              return this.userService.performSecondRequestLogin(response); // <-----

          })
          // Flattened properly here, assuming performSecondRequestLogin 
          // returns a promise
          .then((response) => {
                if (response.status < 500) {
                    console.warn('Login failed!');
                } else {
                    console.error('Internal Server Error');
                }
           })
           // Catch for good measure!
           .catch((error)=>{...});

在Angular2中组合后端调用

2 个答案: