@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”

我的建议是:https://medium.com/@AustinMatherne/ angular-let-direcy-a168d4248138

这个指令允许你这样写:

<div *ngLet="'myVal' as myVar">
  <span> {{ myVar }} </span>
</div>

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。

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));
}

丑,但是:

<div *ngFor="let a of [aVariable]">
  <span>{{a}}</span>
</div>

当与async管道一起使用时:

<div *ngFor="let a of [aVariable | async]">
  <span>{{a.prop1}}</span>
  <span>{{a.prop2}}</span>
</div>