Angular 2：如何返回屬於在一個數組中擴展超類的多個類的對象？

Question

我正在嘗試在Angular 2-Native Script應用程序中創建一個服務，該應用程序定義了一個新聞項目數組，並且具有對相同數據進行操作的多種方法。這些新聞項目可以是不同的類型，例如大，小等，每個參數可能有不同的參數。

我已經定義了接口和服務如下。

import { Injectable } from "@angular/core"; 

export interface NewsItem { 
type: "big" | "small" |"referral"; 
title: string; 
text: string; 
imageUrl?: string; 
} 

export interface Referral extends NewsItem { 
type: "referral"; 
username: string; 
} 


@Injectable() 
export class NewsService { 
    private data = [ 
     { type: "big", title: "This is one big item!", text: "Lorem ipsum  dolor sit amet, consectetur adipiscing elit. Phasellus iaculis, turpis vitae ornare accumsan, arcu tortor ultrices nunc, eu aliquam libero sapien vitae tellus.", imageUrl: "https://octodex.github.com/images/octocat-de-los-muertos.jpg" }, 
     { type: "small", title: "Yes, we code!", text: "Vivamus a sem eget erat feugiat hendrerit at quis massa. Nullam varius ac eros non dignissim. Fusce gravida arcu libero.", imageUrl: "https://octodex.github.com/images/baracktocat.jpg" }, 
     { type: "referral", title: "Yes, we code!", username:"Vasanthi Subramaniam", text: "Vivamus a sem eget erat feugiat hendrerit at quis massa. Nullam varius ac eros non dignissim. Fusce gravida arcu libero.", imageUrl: "https://octodex.github.com/images/baracktocat.jpg" } 
    ] 

private getItems(): NewsItem { 
     let result:NewsItem[] = this.data; 

    return result; 
} 
} 

我正在一個錯誤，如下所示：

Type '({ type: string; title: string; text: string; imageUrl: string; } 
| { type: string; title: string...' is not assignable to type 'NewsItem[]' 

我如何定義數組，使得它分配給新聞項？

Answer 1

只投你的對象明確爲推薦類：

private data = [ 
    { type: "big", title: "This is one big item!", text: "Lorem ipsum  dolor sit amet, consectetur adipiscing elit. Phasellus iaculis, turpis vitae ornare accumsan, arcu tortor ultrices nunc, eu aliquam libero sapien vitae tellus.", imageUrl: "https://octodex.github.com/images/octocat-de-los-muertos.jpg" }, 
    { type: "small", title: "Yes, we code!", text: "Vivamus a sem eget erat feugiat hendrerit at quis massa. Nullam varius ac eros non dignissim. Fusce gravida arcu libero.", imageUrl: "https://octodex.github.com/images/baracktocat.jpg" }, 
    <Referral>{ type: "referral", title: "Yes, we code!", username:"Vasanthi Subramaniam", text: "Vivamus a sem eget erat feugiat hendrerit at quis massa. Nullam varius ac eros non dignissim. Fusce gravida arcu libero.", imageUrl: "https://octodex.github.com/images/baracktocat.jpg" } 
]