import { Directive, Input, TemplateRef, ViewContainerRef } from '@angular/core';
/**
* Add the template content to the DOM unless the condition is true.
*/
@Directive({ selector: '[appUnless]'})
export class UnlessDirective {
private hasView = false;
constructor(
private templateRef: TemplateRef<any>,
private viewContainer: ViewContainerRef) { }
// 这里一个技巧:
// 因为不推荐用Input别名来修饰输入变量,所以可以把这个输入变量用Input函数的形式来输入
@Input() set appUnless(condition: boolean) {
if (!condition && !this.hasView) {
this.viewContainer.createEmbeddedView(this.templateRef);
this.hasView = true;
} else if (condition && this.hasView) {
this.viewContainer.clear();
this.hasView = false;
}
}
}