Question

我正在研究Angular6（打字稿）。我正在尝试用以下代码链接promise ...

public start() {
    this.p1()
      .then(this.p2)
      .then(this.p3)
      .catch((err) => console.log(err));
  }

  public p1(): Promise<string> {
    return new Promise((resolve, reject) => {
      this.httpService.sendHello().subscribe(response => {
        resolve();
      });
    });
  }

  public p2(): Promise<string> {
    return new Promise((resolve, reject) => {
      this.httpService.sendHello().subscribe(response => {
        resolve();
      });
    });
  }

  public p3(): Promise<string> {
    return new Promise((resolve, reject) => {
      this.httpService.sendHello().subscribe(response => {
        resolve();
      });
    });
  }

但是出现错误“无法读取未定义的属性'httpService'”。

我应该如何在promise链中共享angular6服务？

感谢您的帮助，

Answer 1

您将其作为函数的参数，例如：

public start() {
    this.p1(this.httpService)
      .then(this.p2)
      .then(this.p3)
      .catch((err) => console.log(err));
  }

  public p1(httpService: HttpService): Promise<string> {
    return new Promise((resolve, reject) => {
      httpService.sendHello().subscribe(response => {
        resolve();
      });
    });
  }

Answer 2

这是this上下文。将它们转换为箭头函数：

  public p1 = (): Promise<string> => { //...

Answer 3

当您不使用箭头功能时，Typescript不会绑定this。

您可以写then(this.p2)代替then(() => this.p2())

public start() {
    this.p1()
      .then(() => this.p2())
      .then(() => this.p3())
      .catch((err) => console.log(err));
  }

  public p1(): Promise<string> {
    return new Promise((resolve, reject) => {
      this.httpService.sendHello().subscribe(response => {
        resolve();
      });
    });
  }

  public p2(): Promise<string> {
    return new Promise((resolve, reject) => {
      this.httpService.sendHello().subscribe(response => {
        resolve();
      });
    });
  }

  public p3(): Promise<string> {
    return new Promise((resolve, reject) => {
      this.httpService.sendHello().subscribe(response => {
        resolve();
      });
    });
  }

Answer 4

您可以使用RxJS forkjoin，这里是示例

ngOnInit() {
  chainCall().subscribe(resp=> {
   console.log(resp);
  })
}

chainCall(): Observable<any[]> {
const response1 =  this.httpService.sendHello();
const response2 = this.httpService.sendHello();

return forkJoin([response1, response2]);
}

如何在承诺链中共享Angular服务？

4 个答案: