我试图复制一个织物式下拉菜单的外观,在角2.使用有我试图让右边的两个重要的位:为什么我的自定义Angular 2下拉列表中没有填充@ContentChildren?
- 我使用ngModel
- 下拉组件在查询它们之前并不知道它的子项。下拉菜单项将会放在其他的模板中,因为这是需要插入数据的“别的东西”。
这里是我迄今为止的下拉和dropdownItem组成部分:(AbstractValueAccessor来自this other answer)
@Component({
selector: "dropdown",
template: ` <div class="ms-Dropdown" [ngClass]="{'ms-Dropdown--open': isOpen}">
<span class="ms-Dropdown-title" (click)="toggleDropdown()"> {{selectedName}} </span>
<ul class="ms-Dropdown-items">
<ng-content></ng-content>
</ul>
</div>`,
providers: [QueryList]
})
export class FabricDropdownComponent extends AbstractValueAccessor implements AfterContentInit {
public selectedName: string;
public isOpen: boolean;
private subscriptions: Subscription[];
constructor(@ContentChildren(FabricDropdownItemComponent) private items: QueryList<FabricDropdownItemComponent>) {
super();
this.subscriptions = [];
this.selectedName = "Filler text, this should be replaced by 'Thing'";
this.isOpen = false;
}
// HERE'S THE PROBLEM: this.items is an empty array, so I can't find any child components.
public ngAfterContentInit() {
this.items.changes.subscribe((list: any) => {
// On every change, re-subscribe.
this.subscriptions.forEach((sub: Subscription) => sub.unsubscribe());
this.subscriptions = [];
this.items.forEach((item: FabricDropdownItemComponent) => {
this.subscriptions.push(item.onSelected.subscribe((selected: INameValuePair) => {
this.value = selected.value;
this.selectedName = selected.name;
this.isOpen = false;
}));
});
});
// During init, display the *name* of the selected value.
// AGAIN: items is empty, can't set the initial value. What's going on?
this.items.forEach((item: FabricDropdownItemComponent) => {
if (item.value === this.value) {
this.selectedName = item.name;
}
})
}
public toggleDropdown() {
this.isOpen = !this.isOpen;
}
}
@Component({
selector: "dropdownItem",
template: `<li (click)="select()" class="ms-Dropdown-item" [ngClass]="{'ms-Dropdown-item--selected': isSelected }">{{name}}</li>`
})
export class FabricDropdownItemComponent implements OnInit {
@Input() public name: string;
@Input() public value: any;
@Output() public onSelected: EventEmitter<INameValuePair>;
public isSelected: boolean;
constructor() {
this.onSelected = new EventEmitter<INameValuePair>();
this.isSelected = false;
}
public ngOnInit() {
if (!this.name) {
this.name = this.value.toString();
}
}
public select() {
this.onSelected.emit({ name: this.name, value: this.value });
this.isSelected = true;
}
public deselect() {
this.isSelected = false;
}
}
这里就是我如何实际使用它们的应用程序:
<dropdown [(ngModel)]="responseType" ngDefaultControl>
<dropdownItem [value]="'All'"></dropdownItem>
<dropdownItem *ngFor="let r of responseTypes" [value]="r.value" [name]="r.name"></dropdownItem>
</dropdown>
我的问题是@ContentChildr的下拉的QueryList en总是空的,所以当我点击其中一个dropdownItem时,它不会收到通知。为什么QueryList是空的,我该如何解决这个问题?我在这里错过了什么? (我想我可以只使用一个服务在dropdown和dropdownItem之间进行通信,而不是QueryList,但这不是我在这里问的 - 为什么QueryList是空的?)
我试过使用@ViewChildren相反,但没有奏效。我尝试添加了FabricDropdownItemComponent于下拉的指令,但只是给了一个不同的错误:Error: Unexpected directive value 'undefined' on the View of component 'FabricDropdownComponent'
Plunker:https://plnkr.co/edit/D431ihORMR7etrZOBdpW?p=preview
开放的问题是由于(重复)嵌套和HostListener是连接到一个属性指令所附着的元素到,但MutationObserver看起来很有前途,以蛮力的方式。 – PotatoEngineer