Angular 4 Scroll Element Offset Top Value

Question

在jQuery中，element.offset（）。top給出文檔頂部的固定元素當前位置。當我向下滾動時，滾動偏移量最大值時會增長。

現在我需要在Angular 4中的相同行爲，但我缺少一些東西，我的偏移量最高值仍然是相同的。

請參閱附件Plunker：https://embed.plnkr.co/3sDzpRcJMEN6lndw4MUB

@Component({ 
    selector: '[my-app]', 
    template: ` 
    <div> 
     <h2>There is document top</h2> 
     <div class="fixed-box" #fixedBox> 
     <p>I'm fixed box</p> 
     <p>I wanna know my offset from the document top (not viewport) in every scroll step</p> 
     <p>My current position from the document top is: {{ fixedBoxOffsetTop }}px</p> 
     <p>My current position from the document top is: {{ fixedBoxOffsetTopOtherMethod }}px</p> 
     </div> 
    </div> 
    `, 
}) 
export class App implements OnInit { 
    fixedBoxOffsetTop: number = 0; 
    fixedBoxOffsetTopOtherMethod: number = 0; 

    @ViewChild('fixedBox') fixedBox: ElementRef; 

    constructor() {} 

    ngOnInit() {} 

    @HostListener("window:scroll", []) 
    onWindowScroll() { 
    this.fixedBoxOffsetTop = this.fixedBox.nativeElement.offsetTop; // This value looks like init value and doesn't change during scroll 
    this.fixedBoxOffsetTopOtherMethod = this.fixedBox.nativeElement.getBoundingClientRect().top; // The same result as offsetTop 
    } 
} 

有人能幫忙嗎？

Answer 1

你錯過了window和document偏移：

const rect = this.fixedBox.nativeElement.getBoundingClientRect(); 
this.fixedBoxOffsetTop = rect.top + window.pageYOffset - document.documentElement.clientTop; 

Forked Plunker

Answer 2

還有就是我爲這個方法：

getCurrentOffsetTop(element: ElementRef) { 
    const rect = element.nativeElement.getBoundingClientRect(); 
    return rect.top + window.pageYOffset - document.documentElement.clientTop; 
}