Angular 为使用 ng-template 的儿童重复 html

Question

我认为这很简单，但出于某种原因我无法理解。我正在构建一个简单的子菜单。我已经创建了组件：

export class SubMenuComponent implements OnInit {
    @Input() links: MenuItem[];

    constructor() {}

    ngOnInit(): void {}
}

MenuItem 看起来像这样：

export class MenuItem {
    label: string;
    path: string;
    open: boolean;
    children?: MenuItem[];
}

Html 看起来像这样：

<ul class="app-sub-menu list-unstyled">
    <li *ngFor="let link of links" routerLinkActive="active"><a class="btn-link" [routerLink]="link.path"
            routerLinkActive="active" [routerLinkActiveOptions]="{exact: link.path === '/'}">{{ link.label }}</a>

        <span class="toggle" *ngIf="link.children?.length" (click)="link.open = !link.open">
            <mat-icon *ngIf="link.isActive || link.open">keyboard_arrow_down</mat-icon>
            <mat-icon *ngIf="!link.isActive && !link.open">keyboard_arrow_up</mat-icon>
        </span>

        <ul class="list-unstyled" [class.open]="link.open" *ngIf="link.children?.length">
            <li *ngFor="let link of link.children" routerLinkActive="active"><a class="btn-link"
                    routerLinkActive="active" [routerLink]="link.path" #link>{{ link.label }}</a>

                <span class="toggle" *ngIf="link.children?.length" (click)="link.open = !link.open">
                    <mat-icon *ngIf="link.isActive || link.open">keyboard_arrow_down</mat-icon>
                    <mat-icon *ngIf="!link.isActive && !link.open">keyboard_arrow_up</mat-icon>
                </span>

                <ul class="list-unstyled" [class.open]="link.open" *ngIf="link.children?.length">
                    <li *ngFor="let link of link.children" routerLinkActive="active"><a class="btn-link"
                            routerLinkActive="active" [routerLink]="link.path">{{ link.label }}</a>
                    </li>
                </ul>
            </li>
        </ul>
    </li>
</ul>

如您所见，当前的 子菜单 仅向下 3 级。我希望它可以无限嵌套。所以我决定使用 ng-template，但我无法让它工作。我认为这会很简单：

<ul class="app-sub-menu list-unstyled">
    <ng-template *ngTemplateOutlet="link" *ngFor="let link of links"></ng-template>
</ul>

<ng-template #link>
    <li *ngFor="let link of links" routerLinkActive="active"><a class="btn-link" [routerLink]="link.path"
            routerLinkActive="active" [routerLinkActiveOptions]="{exact: link.path === '/'}">{{ link.label }}</a>

        <span class="toggle" *ngIf="link.children?.length" (click)="link.open = !link.open">
            <mat-icon *ngIf="link.isActive || link.open">keyboard_arrow_down</mat-icon>
            <mat-icon *ngIf="!link.isActive && !link.open">keyboard_arrow_up</mat-icon>
        </span>

        <ul class="list-unstyled" [class.open]="link.open" *ngIf="link.children?.length">
            <ng-template *ngTemplateOutlet="link" *ngFor="let link of link.children"></ng-template>
        </ul>
    </li>
</ng-template>

但是当我尝试使用它时，出现错误：

Can't have multiple template bindings on one element. Use only one attribute prefixed with *

所以我改成这样：

现在我收到一个新错误：

templateRef.createEmbeddedView is not a function

有谁知道我该怎么做才能让它发挥作用？

正在阅读：

https://medium.com/@nehaabrol87/the-power-of-angulars-ngtemplateoutlet-used-to-implement-a-nested-data-structure-11c741e6b48c

看来我的模板使用不正确，所以我将其更改为：

<ul class="app-sub-menu list-unstyled">
    <ng-container *ngTemplateOutlet="link; context: { $implicit: links }"></ng-container>
</ul>

<ng-template #link let-links>
    <li *ngFor="let link of links" routerLinkActive="active"><a class="btn-link" [routerLink]="link.path"
            routerLinkActive="active" [routerLinkActiveOptions]="{exact: link.path === '/'}">{{ link.label }}</a>

        <span class="toggle" *ngIf="link.children?.length" (click)="link.open = !link.open">
            <mat-icon *ngIf="link.isActive || link.open">keyboard_arrow_down</mat-icon>
            <mat-icon *ngIf="!link.isActive && !link.open">keyboard_arrow_up</mat-icon>
        </span>

        <ul class="list-unstyled" [class.open]="link.open" *ngIf="link.children?.length">
            <ng-container *ngTemplateOutlet="link; context: { $implicit: link.children }"></ng-container>
        </ul>
    </li>
</ng-template>

但我仍然收到错误:(

templateRef.createEmbeddedView is not a function

Answer 1

我想通了，那是因为我的模板id和实际模型一样。所以我把它改成这样：

<ul class="app-sub-menu list-unstyled">
    <ng-template #nestedList let-links>
        <li *ngFor="let link of links" routerLinkActive="active"><a class="btn-link" [routerLink]="link.path"
                routerLinkActive="active" [routerLinkActiveOptions]="{exact: link.path === '/'}">{{ link.label }}</a>

            <span class="toggle" *ngIf="link.children?.length" (click)="link.open = !link.open">
                <mat-icon *ngIf="link.isActive || link.open">keyboard_arrow_down</mat-icon>
                <mat-icon *ngIf="!link.isActive && !link.open">keyboard_arrow_up</mat-icon>
            </span>

            <ul class="list-unstyled" [class.open]="link.open" *ngIf="link.children?.length">
                <ng-container *ngTemplateOutlet="nestedList; context: { $implicit: link.children }"></ng-container>
            </ul>
        </li>
    </ng-template>
    <ng-container *ngTemplateOutlet="nestedList; context: { $implicit: links }"></ng-container>
</ul>

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