Angularjs 离子2在返回之前检查是否可见

我是离子型和棱角型的新手，来自多年的.NET开发。我正在网上尝试几个例子，用Ionic 2构建登录原型

我让WebAPI在后台工作，只返回JSON true或false，这取决于传递的凭据是否正确

我得到的身份验证提供程序如下所示：

  public login(credentials) {
    if (credentials.email === null || credentials.password === null) {
      return Observable.throw("Please insert credentials");
    } else {

        this.result = this.http.post(this.CONST.APIUrl, JSON.stringify(credentials), new RequestOptions({headers: this.contentHeader})).map(res => res.json())

        if (this.result)
        {
            this.currentUser = new User('Simon', 'saimon@devdactic.com');  
        }

        return this.result;

  }}

public login() {
    this.showLoading()
    this.auth.login(this.registerCredentials).subscribe(allowed => {
      if (allowed) {
        setTimeout(() => {
        this.loading.dismiss();
        this.nav.setRoot(HomePage)
        });
      } else {
        this.showError("Access Denied");
      }
    },
    error => {
      this.showError(error);
    });
  }

登录页面如下所示：

  public login(credentials) {
    if (credentials.email === null || credentials.password === null) {
      return Observable.throw("Please insert credentials");
    } else {

        this.result = this.http.post(this.CONST.APIUrl, JSON.stringify(credentials), new RequestOptions({headers: this.contentHeader})).map(res => res.json())

        if (this.result)
        {
            this.currentUser = new User('Simon', 'saimon@devdactic.com');  
        }

        return this.result;

  }}

public login() {
    this.showLoading()
    this.auth.login(this.registerCredentials).subscribe(allowed => {
      if (allowed) {
        setTimeout(() => {
        this.loading.dismiss();
        this.nav.setRoot(HomePage)
        });
      } else {
        this.showError("Access Denied");
      }
    },
    error => {
      this.showError(error);
    });
  }

目前，它总是让人登录。我理解这是因为this.result总是有一个值。但是，在允许用户登录之前，我如何检查API返回的数据呢？

您可以使用它为可观察到的应用程序创建副作用

在登录功能中：

public login(credentials) {
    if (credentials.email === null || credentials.password === null) {
      return Observable.throw("Please insert credentials");
    } else {

        this.result = this.http.post(this.CONST.APIUrl,
          JSON.stringify(credentials), new RequestOptions({headers: this.contentHeader}))
           .map(res => res.json())
           .do(userData=>{
               //check userData and set current user
               this.currentUser = new User('Simon', 'saimon@devdactic.com');
               return userData;//make sure to return the value to subscribe  
           });
   return result;
  }}