Question

我有一个自定义指令，应该可以根据其他条件添加/删除类。

即

// imports 

@Directive({
    selector: '[customDirective]'
})

export class CustomDirective {
    constructor(service: SomService) {
        // code to add class

        if (service.someCondition()) {
            // code to remove class
        }
    }
}

Answer 1

如果您不想使用ngClass指令（提示：您可以将函数传递给[ngClass]="myClasses()"，如果它会在您的模板中内联杂乱），您可以使用Renderer2要添加一个或多个类：

export class CustomDirective {

   constructor(private renderer: Renderer2,
               private elementRef: ElementRef,
               service: SomService) {
   }

   addClass(className: string, element: any) {
       this.renderer.addClass(element, className);
       // or use the host element directly
       // this.renderer.addClass(this.elementRef.nativeElement, className);
   }

   removeClass(className: string, element: any) {
       this.renderer.removeClass(element, className);
   }

}

Answer 2

当您在Angular中使用指令时，您可能希望使用@HostBinding并绑定到class.your-class以便能够基于谓词添加/删除您的类。您无需在Renderer2中进行DI即可有效地添加/删除类。

例如，在使用Bootstrap和Reactive Forms时，如果您想指示有效或无效的表单字段，则可以执行以下操作：

import { Directive, Self, HostBinding, Input } from '@angular/core';
import { NgControl } from '@angular/forms';

@Directive({
  selector: '[appCheckFormFieldValidity]'
})
export class CheckFormFieldValidity{
  @Input() public class: string;

  constructor(
    @Self() private ngControl: NgControl
  ) { }

  @HostBinding('class.is-valid')
  public get isValid(): boolean {
    return this.valid;
  }

  @HostBinding('class.is-invalid')
  public get isInvalid(): boolean {
    return this.invalid;
  }

  public get valid(): boolean {
    return this.ngControl.valid && 
    (this.ngControl.dirty || this.ngControl.touched);
  }

  public get invalid(): boolean {
    return !this.ngControl.pending &&
      !this.ngControl.valid &&
      (this.ngControl.touched || this.ngControl.dirty);
  }
}

这不是严格的示例，但是它说明了@HostBinding的用法，我在StackBlitz中创建了示例

Answer 3

打开和关闭下拉菜单的指令示例

import { Directive, ElementRef, Renderer2, HostListener, HostBinding } from '@angular/core';

@Directive({
    selector: '[appDropDown]',
})
export class DropsownDirective{

@HostBinding('class.open') isopen = false;
@HostListener('mouseenter') onMouseEnter(){
this.isopen = !this.isopen;
}
@HostListener('mouseleave') onMouseLeave(){
    this.isopen = !this.isopen;
}
}

组件添加指令appDropDown

<div class="col-xs-12">
        <div class="btn-group" appDropDown>
        <button class="btn btn-primary dropdown-toggle">
            Manage Movie <span class="caret"></span>
        </button>
        <ul class="dropdown-menu">
            <li><a href="#">To watching List</a></li>
            <li><a href="#">Edit Movie</a></li>
            <li><a href="#">Delete Movie</a></li>
        </ul>
    </div>

确保将新指令包括在 @NgModule声明

Answer 4

export class CustomDirective {
   classname:string = "magenta";

   constructor(private renderer: Renderer2,
               private elementRef: ElementRef,
               service: SomService) {
   }

   addClass(className: string, element: any) {
        // make sure you declare classname in your main style.css
        this.renderer.addClass(this.elementRef.nativeElement, className);
   }

   removeClass(className: string, element: any) {
       this.renderer.removeClass(this.elementRef.nativeElement,className);
   }

}

如何从指令添加/删除类

4 个答案: