NativeScript 和 Angular2 - 如何绑定对象？

Question

我正在尝试显示来自 REST API 的数据。但是， UI 在加载数据之前呈现。所以我收到以下错误：

Cannot read property 'name' of undefined

如何绑定对象？

组件：

@Component({
    selector: 'foo-detail',
    templateUrl: 'foo.component.html',
    providers: [FooService],
})
export class FooDetailComponent implements OnInit {
    public foo:Foo;

    constructor(private fooService:FooService,
                private route:ActivatedRoute) {
    }

    ngOnInit() {
        this.route.params
            .map(params => params['id'])
            .subscribe(fooId => {
                this.fooService
                    .get(+fooId)
                    .subscribe(res => this.foo = res);
            });
    }
}

服务：

@Injectable()
export class FooService {
    constructor(private http: Http) {}

    get(fooId) {
        return this.http.get('http://api.foo.com/foos/' + fooId)
            .map(res => res.json())
            .map(foo => {
                return new Foo(foo.id, foo.name, foo.description);
            });
    }
}

模板：

<ActionBar [title]="foo.name"></ActionBar>
<GridLayout>
    <Label [text]="foo.description"></Label>
</GridLayout>

Answer 1

您可以使用 ngIf 指令或安全导航运算符 (?)（也称为 Elvis 运算符）"protect" 您的模板：

ngIf 指令

<div *ngIf="foo">
<ActionBar [title]="foo.name"></ActionBar>
<GridLayout>
    <Label [text]="foo.description"></Label>
</GridLayout>
</div>

猫王运算符

<ActionBar [title]="foo?.name"></ActionBar>
<GridLayout>
    <Label [text]="foo?.description"></Label>
</GridLayout>
</div>

我建议阅读official Angular 2 page about ngIf directive to understand how it works, as well as template syntax page about safe nagivation operator (?)。

NativeScript 和 Angular2 - 如何绑定对象？

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