1.5. Angular 2 data display

In this section, we will show you how to display data on the user interface in three ways:

Display the properties of a component through an interpolation expression
Pass through NgFor show array type properties
Pass through NgIf achieve conditional display

1.5.1. Display the properties of a component through an interpolation expression ¶

Interpolation is the easiest way to display the properties of a component in the format {{property name}}.

The following code is created based on the Angular 2 TypeScript environment configuration, where you can download the source code and modify the files mentioned below.

`app/app.component.ts` file: ¶

import { Component } from '@angular/core';
@Component({
  selector: 'my-app',
  template: `
    <h1>{{title}}</h1>
    <h2>My favorite websites: {{mySite}}</h2>
    `
})
export class AppComponent {
  title = 'Site List';
  mySite = 'Rookie Tutorial';
}

Angular will be automatically extracted from the component title and mySite property and is displayed in the browser with the following information

Note: a template is a multiline string enclosed in backquotes (`), not single quotation marks (‘).

1.5.2. Use `ngFor` show array properties ¶

We can also loop out multiple sites and modify the following files:

`app/app.component.ts` file: ¶

import { Component } from '@angular/core';
@Component({
  selector: 'my-app',
  template: `
    <h1>{{title}}</h1>
    <h2>My favorite websites: {{mySite}}</h2>
    <p>Website List:</p>
    <ul>
      <li *ngFor="let site of sites">
        {{ site }}
      </li>
    </ul>
    `
})

export class AppComponent {
  title = 'Site List';
  sites = ['Rookie Tutorial', 'Google', 'Taobao', 'Facebook'];
  mySite = this.sites[0];
}

In the code, we use the template Angular of ngFor instruction to display sites don’t forget every entry in the list \*ngFor leading asterisk (*) in.

After modification, the browser displays as follows:

In the instance ngFor loops an array, in fact ngFor can iterate over any object that can be iterated.

Next, we are in app create under the directory site.ts , the code isas follows:

`app/site.ts` file: ¶

export class Site {
  constructor(
    public id: number,
    public name: string) { }
}

One with a constructor and two properties are defined in the above code: id and name the class.

Then we loop the output. Site analogous name attributes:

`app/app.component.ts` file: ¶

import { Component } from '@angular/core';
import { Site } from './site';

@Component({
  selector: 'my-app',
  template: `
    <h1>{{title}}</h1>
    <h2>My favorite websites: {{mySite.name}}</h2>
    <p>Website List:</p>
    <ul>
      <li *ngFor="let site of sites">
        {{ site.name }}
      </li>
    </ul>
    `
})

export class AppComponent {
  title = 'Site List';
  sites = [
      new Site(1, 'Rookie Tutorial'),
      new Site(2, 'Google'),
      new Site(3, 'Taobao'),
      new Site(4, 'Facebook')
      ];
  mySite = this.sites[0];
}

After modification, the browser displays as follows:

1.5.3. Pass through `NgIf` make conditional display ¶

We can use it. NgIf to set the data that outputs the specified condition.

In the following example, we judge that if there are more than 3 websites, output the prompt message: modify the following app.component.ts file, the code is as follows:

`app/app.component.ts` file: ¶

import { Component } from '@angular/core';
import { Site } from './site';

@Component({
  selector: 'my-app',
  template: `
    <h1>{{title}}</h1>
    <h2>My favorite websites: {{mySite.name}}</h2>
    <p>Website List:</p>
    <ul>
      <li *ngFor="let site of sites">
       {{ site.name }}
      </li>
    </ul>
    <p *ngIf="sites.length > 3">You have many favorite websites!</p>
    `
})

export class AppComponent {
  title = 'Site List';
  sites = [
      new Site(1, 'Rookie Tutorial'),
      new Site(2, 'Google'),
      new Site(3, 'Taobao'),
      new Site(4, 'Facebook')
      ];
  mySite = this.sites[0];
}

After modification, the browser displays as follows, with an additional prompt at the bottom: