3 回答
TA贡献1858条经验 获得超8个赞
这在大多数情况下都有效,但它不是一般的解决方案,因为它依赖于变量的真实性
所以起源答案就像@Keith所说。这是另一种方法。我们可以像创建指令一样*ngIf调用它*ngVar
NG-var.directive.ts
@Directive({
selector: '[ngVar]',
})
export class VarDirective {
@Input()
set ngVar(context: any) {
this.context.$implicit = this.context.ngVar = context;
this.updateView();
}
context: any = {};
constructor(private vcRef: ViewContainerRef, private templateRef: TemplateRef<any>) {}
updateView() {
this.vcRef.clear();
this.vcRef.createEmbeddedView(this.templateRef, this.context);
}
}
使用此*ngVar指令,我们可以使用以下内容
<div *ngVar="false as variable">
<span>{{variable | json}}</span>
</div>
要么
<div *ngVar="false; let variable">
<span>{{variable | json}}</span>
</div>
要么
<div *ngVar="45 as variable">
<span>{{variable | json}}</span>
</div>
要么
<div *ngVar="{ x: 4 } as variable">
<span>{{variable | json}}</span>
</div>
Plunker示例Angular4 ngVar
也可以看看
Angular 4在哪里为* ngIf定义“as local-var”行为?
起源
Angular v4
1)div+ ngIf+let
<div *ngIf="{ a: 1, b: 2 }; let variable">
<span>{{variable.a}}</span>
<span>{{variable.b}}</span>
</div>
2)div+ ngIf+as
视图
<div *ngIf="{ a: 1, b: 2, c: 3 + x } as variable">
<span>{{variable.a}}</span>
<span>{{variable.b}}</span>
<span>{{variable.c}}</span>
</div>
component.ts
export class AppComponent {
x = 5;
}
3)如果你不想像div你可以使用那样创建包装器ng-container
视图
<ng-container *ngIf="{ a: 1, b: 2, c: 3 + x } as variable">
<span>{{variable.a}}</span>
<span>{{variable.b}}</span>
<span>{{variable.c}}</span>
</ng-container>
TA贡献1810条经验 获得超4个赞
丑陋,但是:
<div *ngFor="let a of [aVariable]">
<span>{{a}}</span>
</div>
与异步管道一起使用时:
<div *ngFor="let a of [aVariable | async]">
<span>{{a.prop1}}</span>
<span>{{a.prop2}}</span>
</div>
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