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
更新3
问题https://github.com/angular/angular/issues/2451在Angular 4.0.0中已修复
另请参阅
https://github.com/angular/angular/pull/13297 https://github.com/angular/angular/commit/b4db73d https://github.com/angular/angular/issues/13061
更新2
这是不支持的。
有模板变量,但不支持分配任意值。它们只能用于引用它们应用的元素,导出指令或组件的名称,以及ngFor等结构指令的作用域变量,
参见https://github.com/angular/angular/issues/2451
更新1
@Directive({
selector: '[var]',
exportAs: 'var'
})
class VarDirective {
@Input() var:any;
}
然后像这样初始化
<div #aVariable="var" var="abc"></div>
or
<div #aVariable="var" [var]="'abc'"></div>
然后用这个变量
<div>{{aVariable.var}}</div>
(未测试)
# variable创建对VarDirective的引用(exportAs: 'var') var="abc"实例化VarDirective,并将字符串值"abc"传递给它的值输入。 aVariable。Var读取分配给Var指令Var输入的值。
其他回答
一个简单的解决方案可以满足我的需求:
<ng-container *ngIf="lineItem.productType as variable">
{{variable}}
</ng-container>
OR
<ng-container *ngIf="'ANY VALUE' as variable">
{{variable}}
</ng-container>
我使用的是Angular版本:12。这似乎也适用于其他版本。
它简单得多,不需要任何额外的东西。在我的例子中,我声明变量“open”,然后使用它。
<mat-accordion class="accord-align" #open>
<mat-expansion-panel hideToggle="true" (opened)="open.value=true" (closed)="open.value=false">
<mat-expansion-panel-header>
<span class="accord-title">Review Policy Summary</span>
<span class="spacer"></span>
<a *ngIf="!open.value" class="f-accent">SHOW</a>
<a *ngIf="open.value" class="f-accent">HIDE</a>
</mat-expansion-panel-header>
<mat-divider></mat-divider>
<!-- Quote Details Component -->
<quote-details [quote]="quote"></quote-details>
</mat-expansion-panel>
</mat-accordion>
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$: Observable<number> = defer(() => timer(3000, 1000));
}
更新
我们可以创建像*ngIf这样的指令,并将其命名为*ngVar
ng-var.directive.ts
@Directive({
selector: '[ngVar]',
})
export class VarDirective {
@Input()
set ngVar(context: unknown) {
this.context.$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。
更新3
问题https://github.com/angular/angular/issues/2451在Angular 4.0.0中已修复
另请参阅
https://github.com/angular/angular/pull/13297 https://github.com/angular/angular/commit/b4db73d https://github.com/angular/angular/issues/13061
更新2
这是不支持的。
有模板变量,但不支持分配任意值。它们只能用于引用它们应用的元素,导出指令或组件的名称,以及ngFor等结构指令的作用域变量,
参见https://github.com/angular/angular/issues/2451
更新1
@Directive({
selector: '[var]',
exportAs: 'var'
})
class VarDirective {
@Input() var:any;
}
然后像这样初始化
<div #aVariable="var" var="abc"></div>
or
<div #aVariable="var" [var]="'abc'"></div>
然后用这个变量
<div>{{aVariable.var}}</div>
(未测试)
# variable创建对VarDirective的引用(exportAs: 'var') var="abc"实例化VarDirective,并将字符串值"abc"传递给它的值输入。 aVariable。Var读取分配给Var指令Var输入的值。