Can't access data from Http in Ionic 2

问题:

I'm trying to get the data from Blogspot API using HTTP in Ionic 2. All of my codes are below

This is the service that I created to interface with HTTP and components.

  **HttpService.ts**

 export class Serverdata {
  constructor(private http: Http) { }

  getData() {
   return this.http.get(this.blogUrl)
    .map(
    (response: Response) => {
     const datas = response.json();
     return datas;
     }
    );
   }
 }

This is the component that I created to test the data.

  **Component.ts**

    constructor(public navCtrl: NavController, public navParams: 
                NavParams, private httpData : Serverdata) {}

        serverDataCall(){
           this.httpData.getData().subscribe(
           (datas) => console.log(datas),
           (error) => console.log(error)
           );
        }

And here is the component template

  **Component template**

    <ion-content padding>
    <button ion-button (click) = "serverDataCall()" > get </button>
    </ion-content>

When I click the button, it shows an object in the console which is something like this,

            Object {kind: "blogger#postList", 
             nextPageToken:"CgkIChihsOeVtioQo9Cj3-vl17BF", 
             items: Array(10), 
             etag: 
    ""h3phi6z0oROkI1XWpXsALUFHLuA/MjAxNy0wMy0zMVQwMjoxMzowNy45Mjda""}
     etag:
     ""h3phi6z0oROkI1XWpXsALUFHLuA/MjAxNy0wMy0zMVQwMjoxMzowNy45Mjda""
          items:Array(10)
           0:Object
           1:Object
           2:Object
           3:Object
           4:Object
           5:Object
           6:Object
           7:Object
           8:Object
           9:Object
           length:10
           kind:"blogger#postList"

There are elements such as title and content with in each of the object items. But, I wasn't able to retrieve any of them.

I tried this, but it didn't work!

      serverDataCall(){
           this.httpData.getData().subscribe(
           (datas : any []) => this.data = datas, //changed this line 
           (error) => console.log(error)
           );
          }

And in template,

        <ion-content padding>
        <button ion-button (click) = "serverDataCall()" > get 
         lyrics</button>
           <ion-grid>
            <ion-row *ngFor="let data of datas">
             <ion-col>
              {{data.title}}
             </ion-col>
            </ion-row>
           <ion-grid>
        </ion-content>

Nothing worked! It gives me errors such as undefined!

回答1:

You are getting undefined because your view is loaded before the data is received and your *ngFor is getting datas as undefined initially.

use an *ngIf in the grid to make sure the loop loads after data is received. Also as @echonax suggests it should loop through items.

 <ion-content padding>
        <button ion-button (click) = "serverDataCall()" > get 
         lyrics</button>
           <ion-grid *ngIf="datas && datas.items">
            <ion-row *ngFor="let data of datas.items">
             <ion-col>
              {{data.title}}
             </ion-col>
            </ion-row>
           <ion-grid>
        </ion-content>

回答2:

 serverDataCall(){
       this.httpData.getData().subscribe(
       (datas : any []) => this.data.items = datas, //you can either do this and keep the the template code the same  
       (error) => console.log(error)
       );
      }

2nd way

    <ion-content padding>
    <button ion-button (click) = "serverDataCall()" > get 
     lyrics</button>
       <ion-grid>
        <ion-row *ngFor="let data of datas.items"> // or change it in the template and leave the service method unchanged
         <ion-col>
          {{data.title}}
         </ion-col>
        </ion-row>
       <ion-grid>
    </ion-content>