Question

我为我的角度项目创建了一个指令，该指令向后端API发出请求以获取许多国家/地区，然后使用ngFor填充选择器的选项。您可以在下面看到它们的结构：

select.component.html：

<div class="col-sm-10" (countriesFetched)="populateCountriesList($event)" appGetCountriesList>
    <select id="countrySelector" class="form-control" [(ngModel)]='coutryOption' (ngModelChange)='countrySelected($event)' required>
        <option *ngFor="let country of countriesList;"  [ngValue]=country [selected]="country.name === countryToDisplay? selected:null">{{country.name}}</option>
    </select>
</div>

select.component.ts

@Component({
    selector: 'app-selector',
    templateUrl: './selector.component.html',
    styleUrls: ['./selector.component.scss'],
})

export class SelectorComponent implements OnInit {
    @Input('countryToDisplay') countryToDisplay: string
    @Output() shippingCountryChanged: EventEmitter<string> = new EventEmitter();
    countriesList: Object[];
    singleCountry: boolean;

    constructor () { }

    ngOnInit() {
        this.singleCountry = false;
     }

    populateCountriesList(countries) {
        this.countriesList = countries;
    }
    countrySelected(e) {
        this.shippingCountryChanged.emit(e);
    }
}

selector.directive.ts

@Directive({
    selector: '[appGetCountriesList]'
})

export class DropdownDirective {
    @Output() countriesFetched = new EventEmitter<any>();
    countrylist: Object[] = [];
    constructor ( private countriesService: CountriesService ) {
        this.getCountries();
    }

    getCountries() {
        if (this.countrylist.length === 0) {
            const market = localStorage.getItem('marketCode');
            this.countriesService.fetchCountries(market).subscribe( res => {
                res = res['countries'];
                Object.keys(res).map( key => {
                     if ( res[key].name.length > 0 && parseInt(res[key].is_enabled, 10) === 1) {
                     this.countrylist.push(res[key]);
                    }
                 });
                 this.countrylist = this.countrylist.sort();
                 this.countriesFetched.emit(this.countrylist);
            });
        }
    }
}

选择国家/地区后，会发出一个事件，整个应用程序会使用新值自行更新。

我的问题是，我怎样才能获得用户选择的预选值，也许是在他们刷新页面之后？我试图将预选值作为组件的输入传递，如.html文件中所示，但选择器仍为空，直到用户选择新值。

Answer 1

这可能是一种非常粗暴的方式：

<select id="countrySelector" class="form-control" [(ngModel)]='coutryOption' (ngModelChange)='countrySelected($event)' required>
    <ng-container *ngFor="let country of countriesList;">
        <ng-container *ngIf="country.name === countryToDisplay">
            <option [ngValue]=country selected>{{country.name}}
            </option>
        </ng-container>
        <ng-container *ngIf="country.name !== countryToDisplay">
            <option [ngValue]=country>{{country.name}}
            </option>
        </ng-container>
    </ng-container>
</select>

Answer 2

类似于@Praveen Kumar的答案，但是如果有帮助的话，我会使用它：

<select class="form-control" [(ngModel)]="countryOption">
   <ng-template [ngIf]="select">
      <option value=''>{{select}}</option>
      <option *ngFor="let country of countryList" type="text" [ngValue]="country.name">{{country.name}}</option>
   </ng-template>
   <ng-template [ngIf]="!select">
      <option *ngFor="let country of countryList" type="text" [ngValue]="country.name">{{country.name}}</option>
   </ng-template>
</select>

Answer 3

在摆弄选择表格后，结果发现[（ngModel）] =＆＃39; coutryOption＆＃39;在init上没有设置任何内容。

所以我将组件更改为：

export class CountrySelectorComponent {
@Input('countryToDisplay') countryToDisplay: string;
@Output() shippingCountryChanged: EventEmitter<string> = new EventEmitter();
countriesList: Object[];
countryOption: object;
constructor () { }

populateCountriesList(countries) {
    this.countriesList = countries;
    this.countryOption = this.countriesList.filter(country => {
        return country['name'] === this.countryToDisplay
    });
    this.countryOption = this.countryOption[0];
}
countrySelected(e) {
    this.shippingCountryChanged.emit(e);
 }
}

，html看起来像这样：

<div class="col-sm-10" (countriesFetched)="populateCountriesList($event)" appGetCountriesList>
    <select id="countrySelector" class="form-control" [(ngModel)]='countryOption' (ngModelChange)='countrySelected($event)' required>
        <option *ngFor="let country of countriesList;"  [ngValue]=country >{{country.name}}</option>
    </select>
</div>

这适用于其＆＃39;预期目的。谢谢你的答案！

在Angular

3 个答案: