我有以下模板:
<div>
<span>{{aVariable}}</span>
</div>
并希望以:
<div "let a = aVariable">
<span>{{a}}</span>
</div>
有办法吗?
我有以下模板:
<div>
<span>{{aVariable}}</span>
</div>
并希望以:
<div "let a = aVariable">
<span>{{a}}</span>
</div>
有办法吗?
当前回答
像这样试试
<ng-container
[ngTemplateOutlet]="foo"
[ngTemplateOutletContext]="{ test: 'Test' }"
></ng-container>
<ng-template #foo let-test="test">
<div>{{ test }}</div>
</ng-template>
其他回答
@yurzui的原始答案将不能从Angular 9开始工作,因为一个奇怪的问题,将Angular 8应用程序迁移到9。 然而,你仍然可以从ngVar指令中受益
<ng-template [ngVar]="variable">
your code
</ng-template>
尽管它可能会导致IDE警告:“变量未定义”
更新
我们可以创建像*ngIf这样的指令,并将其命名为*ngVar
ng-var.directive.ts
@Directive({
selector: '[ngVar]',
})
export class VarDirective {
@Input()
set ngVar(context: unknown) {
this.context.$implicit = this.context.ngVar = context;
if (!this.hasView) {
this.vcRef.createEmbeddedView(this.templateRef, this.context);
this.hasView = true;
}
}
private context: {
$implicit: unknown;
ngVar: unknown;
} = {
$implicit: null,
ngVar: null,
};
private hasView: boolean = false;
constructor(
private templateRef: TemplateRef<any>,
private vcRef: ViewContainerRef
) {}
}
对于这个*ngVar指令,我们可以使用以下方法
<div *ngVar="false as variable">
<span>{{variable | json}}</span>
</div>
or
<div *ngVar="false; let variable">
<span>{{variable | json}}</span>
</div>
or
<div *ngVar="45 as variable">
<span>{{variable | json}}</span>
</div>
or
<div *ngVar="{ x: 4 } as variable">
<span>{{variable | json}}</span>
</div>
Angular4 ngVar
另请参阅
Angular 4在哪里为*ngIf定义了“as local-var”行为?
原来的答案
角v4
div + ngIf + let {{variable.a}} {{variable.b}} div + ngIf + as
view
<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;
}
如果你不想创建像div这样的包装器,你可以使用ng-container
view
<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>
正如@Keith在评论中提到的
这将在大多数情况下工作,但它不是一个普遍的解决方案,因为它 依赖于变量为真
有关另一种方法,请参阅update。
对于那些决定使用结构指令代替*ngIf的人,请记住,默认情况下指令上下文不进行类型检查。要创建一个类型安全的指令,应该添加ngTemplateContextGuard属性,请参见输入指令的上下文。例如:
import { Directive, Input, TemplateRef, ViewContainerRef } from '@angular/core';
@Directive({
// don't use 'ng' prefix since it's reserved for Angular
selector: '[appVar]',
})
export class VarDirective<T = unknown> {
// https://angular.io/guide/structural-directives#typing-the-directives-context
static ngTemplateContextGuard<T>(dir: VarDirective<T>, ctx: any): ctx is Context<T> {
return true;
}
private context?: Context<T>;
constructor(
private vcRef: ViewContainerRef,
private templateRef: TemplateRef<Context<T>>
) {}
@Input()
set appVar(value: T) {
if (this.context) {
this.context.appVar = value;
} else {
this.context = { appVar: value };
this.vcRef.createEmbeddedView(this.templateRef, this.context);
}
}
}
interface Context<T> {
appVar: T;
}
该指令可以像*ngIf一样使用,除了它可以存储假值:
<ng-container *appVar="false as value">{{value}}</ng-container>
<!-- error: User doesn't have `nam` property-->
<ng-container *appVar="user as user">{{user.nam}}</ng-container>
<ng-container *appVar="user$ | async as user">{{user.name}}</ng-container>
与*ngIf相比,唯一的缺点是Angular语言服务无法识别变量类型,因此模板中没有代码补全功能。我希望它能很快修好。
我使用的是angular 6x,我最终使用了下面的代码片段。 我有一个需要从任务对象中查找user的场景。它包含用户数组,但我必须选择分配的用户。
<ng-container *ngTemplateOutlet="memberTemplate; context:{o: getAssignee(task) }">
</ng-container>
<ng-template #memberTemplate let-user="o">
<ng-container *ngIf="user">
<div class="d-flex flex-row-reverse">
<span class="image-block">
<ngx-avatar placement="left" ngbTooltip="{{user.firstName}} {{user.lastName}}" class="task-assigned" value="28%" [src]="user.googleId" size="32"></ngx-avatar>
</span>
</div>
</ng-container>
</ng-template>
我是https://www.npmjs.com/package/ng-let的作者
将数据作为局部变量共享到html组件模板的结构指令。
源代码:
import { Directive, Input, TemplateRef, ViewContainerRef } from '@angular/core';
interface NgLetContext<T> {
ngLet: T;
$implicit: T;
}
@Directive({
// tslint:disable-next-line: directive-selector
selector: '[ngLet]'
})
export class NgLetDirective<T> {
private context: NgLetContext<T | null> = { ngLet: null, $implicit: null };
private hasView: boolean = false;
// eslint-disable-next-line no-unused-vars
constructor(private viewContainer: ViewContainerRef, private templateRef: TemplateRef<NgLetContext<T>>) { }
@Input()
set ngLet(value: T) {
this.context.$implicit = this.context.ngLet = value;
if (!this.hasView) {
this.viewContainer.createEmbeddedView(this.templateRef, this.context);
this.hasView = true;
}
}
/** @internal */
public static ngLetUseIfTypeGuard: void;
/**
* Assert the correct type of the expression bound to the `NgLet` input within the template.
*
* The presence of this static field is a signal to the Ivy template type check compiler that
* when the `NgLet` structural directive renders its template, the type of the expression bound
* to `NgLet` should be narrowed in some way. For `NgLet`, the binding expression itself is used to
* narrow its type, which allows the strictNullChecks feature of TypeScript to work with `NgLet`.
*/
static ngTemplateGuard_ngLet: 'binding';
/**
* Asserts the correct type of the context for the template that `NgLet` will render.
*
* The presence of this method is a signal to the Ivy template type-check compiler that the
* `NgLet` structural directive renders its template with a specific context type.
*/
static ngTemplateContextGuard<T>(dir: NgLetDirective<T>, ctx: any): ctx is NgLetContext<Exclude<T, false | 0 | '' | null | undefined>> {
return true;
}
}
用法:
import { Component } from '@angular/core';
import { defer, Observable, timer } from 'rxjs';
@Component({
selector: 'app-root',
template: `
<ng-container *ngLet="timer$ | async as time"> <!-- single subscription -->
<div>
1: {{ time }}
</div>
<div>
2: {{ time }}
</div>
</ng-container>
`,
})
export class AppComponent {
timer$: Observable<number> = defer(() => timer(3000, 1000));
}