我一直在使用Angular 4构建一个新站点,我正在尝试重新创建一个效果,当div变为可见时(向下滚动屏幕)然后可以触发角度动画以滑动div形式双方.
我以前在Angular 4之外使用jQuery已经能够做到这一点,但我想尝试使用原生的Angular 4动画创建相同的效果.
任何人都可以向我提供有关如何在div进入视图时触发动画的建议(即,当它进入视口时向下滚动到页面的下半部分？).我已经编写了幻灯片动画但我不知道如何在以后将div显示到视口时使用滚动触发它.
感谢大家！
我创建了一个指令,只要元素完全在视图中或者它的上边缘已到达视图的上边缘,就会发出一个事件.
这是一个吸烟者：https://embed.plnkr.co/mlez1dXjR87FNBHXq1YM/
它的使用方式如下：
<div (appear)="onAppear()">...</div>
这是指令：
import {
ElementRef,Output,Directive,AfterViewInit,OnDestroy,EventEmitter
} from '@angular/core';
import {Observable} from 'rxjs/Observable';
import {Subscription} from 'rxjs/Subscription';
import 'rxjs/add/observable/fromEvent';
import 'rxjs/add/operator/startWith';
@Directive({
selector: '[appear]'
})
export class AppearDirective implements AfterViewInit,OnDestroy {
@Output()
appear: EventEmitter<void>;
elementPos: number;
elementHeight: number;
scrollPos: number;
windowHeight: number;
subscriptionScroll: Subscription;
subscriptionResize: Subscription;
constructor(private element: ElementRef){
this.appear = new EventEmitter<void>();
}
saveDimensions() {
this.elementPos = this.getOffsetTop(this.element.nativeElement);
this.elementHeight = this.element.nativeElement.offsetHeight;
this.windowHeight = window.innerHeight;
}
saveScrollPos() {
this.scrollPos = window.scrollY;
}
getOffsetTop(element: any){
let offsetTop = element.offsetTop || 0;
if(element.offsetParent){
offsetTop += this.getOffsetTop(element.offsetParent);
}
return offsetTop;
}
checkVisibility(){
if(this.isVisible()){
// double check dimensions (due to async loaded contents,e.g. images)
this.saveDimensions();
if(this.isVisible()){
this.unsubscribe();
this.appear.emit();
}
}
}
isVisible(){
return this.scrollPos >= this.elementPos || (this.scrollPos + this.windowHeight) >= (this.elementPos + this.elementHeight);
}
subscribe(){
this.subscriptionScroll = Observable.fromEvent(window,'scroll').startWith(null)
.subscribe(() => {
this.saveScrollPos();
this.checkVisibility();
});
this.subscriptionResize = Observable.fromEvent(window,'resize').startWith(null)
.subscribe(() => {
this.saveDimensions();
this.checkVisibility();
});
}
unsubscribe(){
if(this.subscriptionScroll){
this.subscriptionScroll.unsubscribe();
}
if(this.subscriptionResize){
this.subscriptionResize.unsubscribe();
}
}
ngAfterViewInit(){
this.subscribe();
}
ngOnDestroy(){
this.unsubscribe();
}
}
