如何从指令中添加/删除类

Question

使用自定义指令，您将如何根据特定条件在宿主元素上添加/删除类？

示例：

@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：如果您的模板中的内联混乱，您可以将函数传递给[ngClass]="myClasses()"）您可以使用Renderer2 来实现添加一个或多个类：

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，当使用 Bootstrap 和 Reactive Forms 并且您想指示有效或无效的表单字段时，您可以执行以下操作：

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);
  }
}

这不是一个严格的例子，但它说明了@HostBinding的使用，我在StackBlitz中创建了例子

Answer 3

在下拉菜单中打开和关闭切换的指令示例

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);
   }

}