Angular 2`this`引用在Promise中

Question

My service has the following code:

....
isAuthenticated(){
      var tt = this;
      if(tt.current_user){
          return Promise.resolve(tt.current_user,false);
      }else{
          return new Promise(resolve => {
              this.http.get(this.api.urlBase+this.api.apiBase+'/Individuals/me',
                           {withCredentials: true})
              .map(res=>res.json())
              .subscribe((data) => {
                  tt.current_user = data;
                  resolve(data,false);
              },(err)=>{
                  reject(err,true);
              });
          })
      }
  }
....

And in my page class, I am trying to access it as:

constructor(){
...
let tt = this;
individual.isAuthenticated().then(this.handleLogin);
...
}
...
handleLogin(d,err){
        console.log("This: ",this);
        console.log("This: ",tt);
        this.nav.present(this.loading);
    }

but in handleLogin , this.nav throws an error that this is undefined, and the console logs show this as blank and tt as undefined. How do I reference this from within that function?

Answer 1

You need either to wrap the method call or call the bind method on it

constructor() {
  ...
  let tt = this;
  individual.isAuthenticated().then((data) => { // <----
    this.handleLogin(data)
  });
  ...
}
...
handleLogin(d,err){
    console.log("This: ",this);
    console.log("This: ",tt);
    this.nav.present(this.loading);
}

or

constructor() {
  ...
  let tt = this;
  individual.isAuthenticated().then(this.handleLogin.bind(this));
  ...
}
...
handleLogin(d,err){
    console.log("This: ",this);
    console.log("This: ",tt);
    this.nav.present(this.loading);
}

There is a drawback to use the bind method in TypeScript since you lose type safety of the original function signature. See this link for more details:

• https://basarat.gitbooks.io/typescript/content/docs/tips/bind.html

Answer 2

Define handleLogin as a property rather than a method

//handleLogin(d,err){
handleLogin = (d,err) => {
    console.log("This: ",this);
    console.log("This: ",tt);
    this.nav.present(this.loading);
}

This will keep the this working as expected