Question

遵循Angular 2教程。我正在尝试将以下方法从promises转换为observables。我的尝试如下。

1）转换是否正确？

2）我如何转换getGroup()方法

getGroups（）

  // Promise
  getGroups(): Promise<Group[]> {
    return this.http.get(this.groupsUrl)
      .toPromise()
      .then(response => response.json().data as Group[])
      .catch(this.handleError);
  }
  // Observable
  getGroups(): Observable<Group[]> {
    return this.http.get(this.groupsUrl)
      .map(this.extractData)
      .catch(this.handleError);
  }
  private extractData(response: Response) {
    let body = response.json();
    return body.data || { };
  }

getGroup（）

  // Promise
  getGroup(id: number): Promise<Group> {
    return this.getGroups()
      .then(groups => groups.find(group => group.id === id));
  }
  // Observable
  // ================
  // HOW?
  // ================

createGroup（）

  // Promise
  createGroup(name: string): Promise<Group> {
    return this.http
      .post(this.groupsUrl, JSON.stringify({name: name}), {headers: this.headers})
      .toPromise()
      .then(res => res.json().data)
      .catch(this.handleError);
  }
  // Observable
  createGroup(name: string): Observable<Group> {
    return this.http
      .post(this.groupsUrl, JSON.stringify({name: name}), {headers: this.headers})
      .map(res => res.json().data)
      .catch(this.handleError);
  }

updateGroup（）

  // Promise
  updateGroup(group: Group): Promise<Group> {
    const url = `${this.groupsUrl}/${group.id}`;
    return this.http
      .put(url, JSON.stringify(group), {headers: this.headers})
      .toPromise()
      .then(() => group)
      .catch(this.handleError);
  }
  // Observable
  updateGroup(group: Group): Observable<Group> {
    const url = `${this.groupsUrl}/${group.id}`;
    return this.http
      .put(url, JSON.stringify(group), {headers: this.headers})
      .map(() => group)
      .catch(this.handleError);
  }

deleteGroup（）

  // Promise
  deleteGroup(id: number): Promise<void> {
    const url = `${this.groupsUrl}/${id}`;
    return this.http
      .delete(url, {headers: this.headers})
      .toPromise()
      .then(() => null)
      .catch(this.handleError);
  }
  // Observable
  deleteGroup(id: number): Observable<void> {
    const url = `${this.groupsUrl}/${id}`;
    return this.http
      .delete(url, {headers: this.headers})
      .map(() => null)
      .catch(this.handleError);
  }

}

Answer 1

1）转换是否正确？

转换似乎不正确。通过将function引用传递给可观察的回调，您将失去this上下文。您必须使用Arrow function与this＆amp;明确地调用函数。

// Observable
getGroups(): Observable<Group[]> {
    return this.http.get(this.groupsUrl)
      .map(this.extractData) //don't pass function reference
      .catch(this.handleError);
}

应该是

// Observable
getGroups(): Observable<Group[]> {
  return this.http.get(this.groupsUrl)
    //.map(this.extractData.bind()) //this would work but its bad pattern
    .map(()=> this.extractData())
    .catch(this.handleError);
}

如果你在代码中的某个地方做了同样的事情，那么对其他函数也要做同样的事情。

2）我如何转换getGroup（）方法

它将如下所示

getGroup(id: number): Promise<Group> {
    return this.getGroups()
      .map(groups => groups.find(group => group.id === id));
}

角度2承诺可观察

1 个答案: