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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 | 4x 4x 6x 6x 6x 6x 6x 6x 1x 1x 1x 1x 1x 1x 1x 7x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x 1x | import {
ChangeDetectorRef,
Component,
ContentChild,
ElementRef,
Input,
OnDestroy,
OnInit,
Renderer2,
TemplateRef
} from '@angular/core';
/**
* A block of component that listens to inView and outView events,
* so that it empties contents when out of view after backup items
* and restores the contents when in view
### Example
```html
<ngui-inview-page [items]="items">
<ng-template let-items="items">
<div *ngIf="items else noItems">
<li *ngFor="let num of items; trackBy: num">row number: {{ num }}</li>
</div>
</ng-template>
</ngui-inview-page>
```
*/
@Component({
selector: 'ngui-inview-page',
template: `
<div class="inview-page contents"
[observerOptions]="observerOptions"
(nguiInview)="restoreItems()"
(nguiOutview)="emptyItems()">
<!-- add blank ngui-list-item by condition -->
<!-- no match found ngui-list-item by condition -->
<ng-container
[ngTemplateOutlet]="template||defaultTemplate"
[ngTemplateOutletContext]="{items: items, outView: outView}">
</ng-container>
</div>
<ng-template #defaultTemplate>
<div *ngIf="!items"> Error: requires [items] </div>
<div *ngIf="!template"> Error: requires <ng-template></div>
</ng-template>
`,
styles: [`
:host {display: block}
`]
})
export class NguiInviewPageComponent implements OnInit, OnDestroy {
/** Allow users to change the contents */
@ContentChild(TemplateRef, {static: true}) template: TemplateRef<any>;
// @Input('template') template: TemplateRef<any>;
/** List of elements that are used to render this element */
@Input() items: Array<any>;
/** IntersectionObserver options */
@Input() observerOptions: IntersectionObserverInit = {threshold: [0, .01]};
/** Indicates that the page of out of viewport */
outView = false;
/** The copy of items. This is set when this element is out of viewport */
itemsBackup: Array<any> = [];
/**
* The first element of this component.
* The height of it remains the same even when items get empty out.
*/
contentsEl: HTMLElement;
destroyed: boolean;
constructor(
private element: ElementRef,
private renderer: Renderer2,
private cdRef: ChangeDetectorRef
) { }
/**
* Restore items when in viewport, so that elements are rendered
*/
restoreItems(): void {
if (this.outView) {
this.outView = false;
this.items = Array.from(this.itemsBackup || []);
this.itemsBackup = undefined;
this.renderer.setStyle(this.contentsEl, 'height', undefined);
this.cdRef.detectChanges();
}
}
ngOnInit(): void {
this.contentsEl =
this.element.nativeElement.querySelector('.inview-page.contents');
}
ngOnDestroy(): void {
this.destroyed = true;
}
/**
* Empty items when not in viewport, so that elements are not rendered
*/
emptyItems(): void {
if (this.items && this.contentsEl && !this.outView) {
// set height before emptying contents
const height = this.element.nativeElement.getBoundingClientRect().height;
this.renderer.setStyle(this.contentsEl, 'height', `${height}px`);
this.outView = true;
this.itemsBackup = Array.from(this.items || []);
this.items = undefined;
if (!this.destroyed) {
this.cdRef.detectChanges();
}
}
}
setItems(items: Array<any>): void {
if (!this.destroyed) {
this.items = items;
this.cdRef.detectChanges();
}
}
}
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