從 Angular 2 中的 JSON 對象獲取嵌套數據

Question

你好，我正在構建類似於音樂播放器應用程序的東西。 我有一個服務設置從我在夾具中的 JSON 文件中獲取數據。 我可以使用 *ngFor 獲取所有頂級數據，但是一旦我開始請求諸如 song.parts.name 之類的東西，它就會顯示未定義。

我有 *ngFor 在頁面上吐出頂級鍵值對，然后我希望能夠點擊特定的歌曲名稱並讓它過濾數據以找到正確的歌曲網址。

如何遍歷該數組並獲取這些對象？

任何幫助將非常感激。

JSON

{
  "songs": [
    {
      "name": "America The Beautiful",
      "difficulty": "Medium",
      "time": "3:38",
      "hasPianoWords": true,
      "hasPianoSolfa": false,
      "hasTrackWords": false,
      "parts": [
        {
          "name": "Baritone",
          "urls": {
            "pianoWords": "http://www.taabc.org/check-off-songs/baritone/america-the-beautiful/america-the-beautiful-piano-words.mp3",
            "pianoSolfa": "http://www.taabc.org/check-off-songs/baritone/america-the-beautiful/america-the-beautiful-piano-words.mp3",
            "trackWords": "http://www.taabc.org/check-off-songs/baritone/america-the-beautiful/america-the-beautiful-piano-words.mp3"
          }
        },
        {
          "name": "Bass",
          "urls": {
            "pianoWords": "http://www.taabc.org/check-off-songs/bass/america-the-beautiful/america-the-beautiful-piano-words.mp3",
            "pianoSolfa": "http://www.taabc.org/check-off-songs/bass/america-the-beautiful/america-the-beautiful-piano-words.mp3",
            "trackWords": "http://www.taabc.org/check-off-songs/bass/america-the-beautiful/america-the-beautiful-piano-words.mp3"
          }
        },
        {
          "name": "Second Tenor",
          "urls": {
            "pianoWords": "http://www.taabc.org/check-off-songs/second-tenor/america-the-beautiful/america-the-beautiful-piano-words.mp3",
            "pianoSolfa": "http://www.taabc.org/check-off-songs/second-tenor/america-the-beautiful/america-the-beautiful-piano-words.mp3",
            "trackWords": "http://www.taabc.org/check-off-songs/second-tenor/america-the-beautiful/america-the-beautiful-piano-words.mp3"
          }
        },
        {
          "name": "First Tenor",
          "urls": {
            "pianoWords": "http://www.taabc.org/check-off-songs/first-tenor/america-the-beautiful/america-the-beautiful-piano-words.mp3",
            "pianoSolfa": "http://www.taabc.org/check-off-songs/first-tenor/america-the-beautiful/america-the-beautiful-piano-words.mp3",
            "trackWords": "http://www.taabc.org/check-off-songs/first-tenor/america-the-beautiful/america-the-beautiful-piano-words.mp3"
          }
        }
      ]
    }
  ]
}

Songs.Service.ts

export class SongService {
    constructor(private _http: Http) {}

    getAllSongs() {
        return this._http.get('/fixtures/songs.json')
            .map((response: Response) => response.json().songs)
            .toPromise()
            .catch(this.handleError);
    }

    getSongByName(songName:string) {
        return this._http.get('/fixtures/songs.json')
            .map((response: Response) => _.find(response.json().songs, {'name': songName}))
            .toPromise()
            .catch(this.handleError);
    }

歌曲組件

export class SongsComponent {
    public songs: any;
    public activeSong: any;
    public activeSongURL: any;

    constructor(private _songsService: SongService, private router: Router, private route: ActivatedRoute) {
    }

    ngOnInit() {
        this._songsService.getAllSongs().then(result => {
            this.songs = result;
            console.log('Songs: ', this.songs);
        });
    }

    playSong(songName:string) {
        console.log('clicked song:', songName)

        this._songsService.getSongByName(songName).then(result => {
            this.activeSong = result;
            console.log('active song', this.activeSong);
            this.activeSongURL = this.activeSong.baritone.pianoWords;
            console.log(this.activeSongURL);
        })
    }

    selectSong(songName:string) {
        this.router.navigate(['/song'], songName);
    }
}

HTML模板

<section class="songs container">
    <div class="song col-md-3" *ngFor="let song of songs">
        <h4 (click)="selectSong(song.name)">{{song.name}}</h4>
        <span>Difficulty: {{song.difficulty}}</span>
        <span>Time: {{song.time}}</span>
        <span><strong>Baritone</strong></span>
        <span *ngIf="song.hasPianoSolfa" class="piano-solfa"><i class="fa fa-play-circle-o" aria-hidden="true"></i>Piano Solfa</span>
        <span (click)="playSong(song.name)" *ngIf="song.hasPianoWords" class="piano-words"><i class="fa fa-play-circle-o" aria-hidden="true"></i>Piano Words</span>
        <span (click)="playSong(song.name)" *ngIf="song.hasTrackWords" class="track-words"><i class="fa fa-play-circle-o" aria-hidden="true"></i>Track Words</span>
    </div>
</section>

<section class="audio-player">
    <audio src="{{activeSongURL}}" autoplay controls="controls">
        Your browser does not support the <code>audio</code> element.
    </audio>
</section>

Answer 1

您可以使用Safe-Navigation-Operator

看起來你可能擁有它或接近擁有它，它不應該像

<section class="songs container">
    <div class="song col-md-3" *ngFor="let song of songs">
        <h4 (click)="selectSong(song.name)">{{song.name}}</h4>
        <span>Difficulty: {{song.difficulty}}</span>
        <span>Time: {{song.time}}</span>

        <div *ngIf="song?.parts.length > 0">

            <div *ngFor="let part of song?.parts">
                <strong>{{ part.name }}</strong>
                <span class="piano-words" (click)="playSong(song.name)"><i class="fa fa-play-circle-o" aria-hidden="true"></i>Piano Words</span>
                <span class="piano-solfa" (click)="playSong(song.name)"><i class="fa fa-play-circle-o" aria-hidden="true"></i>Piano Solfa</span>
                <span class="track-words" (click)="playSong(song.name)"><i class="fa fa-play-circle-o" aria-hidden="true"></i>Track Words</span>
            </div>

        </div>

        <!-- <span><strong>Baritone</strong></span>
        <span *ngIf="song.hasPianoSolfa" class="piano-solfa"><i class="fa fa-play-circle-o" aria-hidden="true"></i>Piano Solfa</span>
        <span (click)="playSong(song.name)" *ngIf="song.hasPianoWords" class="piano-words"><i class="fa fa-play-circle-o" aria-hidden="true"></i>Piano Words</span>
        <span (click)="playSong(song.name)" *ngIf="song.hasTrackWords" class="track-words"><i class="fa fa-play-circle-o" aria-hidden="true"></i>Track Words</span>
    </div> -->
</section>