我喜欢创建一个指令来做这件事的方法(很好的调用@yurzui)。

最后我在Medium上找到了一篇文章，Angular的“let”指令很好地解释了这个问题，并提出了一个自定义的let指令，它在我的用例中工作得很好，代码更改很少。

以下是要点(在发布时)和我的修改:

import { Directive, Input, TemplateRef, ViewContainerRef } from '@angular/core'

interface LetContext <T> {
  appLet: T | null
}

@Directive({
  selector: '[appLet]',
})
export class LetDirective <T> {
  private _context: LetContext <T> = { appLet: null }

  constructor(_viewContainer: ViewContainerRef, _templateRef: TemplateRef <LetContext <T> >) {
    _viewContainer.createEmbeddedView(_templateRef, this._context)
  }

  @Input()
  set appLet(value: T) {
    this._context.appLet = value
  }
}

我的主要改变是:

将前缀从'ng'更改为'app'(你应该使用你的应用程序的自定义前缀是什么) 将appLet: T更改为appLet: T | null

不知道为什么Angular团队还没有发布一个官方的ngLet指令。

原始源代码归功于@AustinMatherne

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>

下面是我编写的一个指令，它扩展了exportAs装饰器参数的使用，并允许您使用字典作为局部变量。

import { Directive, Input } from "@angular/core";
@Directive({
    selector:"[localVariables]",
    exportAs:"localVariables"
})
export class LocalVariables {
    @Input("localVariables") set localVariables( struct: any ) {
        if ( typeof struct === "object" ) {
            for( var variableName in struct ) {
                this[variableName] = struct[variableName];
            }
        }
    }
    constructor( ) {
    }
}

你可以在模板中使用它:

<div #local="localVariables" [localVariables]="{a: 1, b: 2, c: 3+2}">
   <span>a = {{local.a}}</span>
   <span>b = {{local.b}}</span>
   <span>c = {{local.c}}</span>
</div>

当然，#local可以是任何有效的局部变量名。

在Angular 12中:

  <div *ngIf="error$ | async as error">
     <span class="text-warn">{{error.message}}</span>
   </div>

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));
}

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>