45 lines
1.4 KiB
TypeScript
45 lines
1.4 KiB
TypeScript
import {Directive, ViewContainerRef, TemplateRef} from '@angular/core';
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import {isBlank} from '../facade/lang';
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/**
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* Removes or recreates a portion of the DOM tree based on an {expression}.
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*
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* If the expression assigned to `ngIf` evaluates to a false value then the element
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* is removed from the DOM, otherwise a clone of the element is reinserted into the DOM.
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*
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* ### Example ([live demo](http://plnkr.co/edit/fe0kgemFBtmQOY31b4tw?p=preview)):
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*
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* ```
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* <div *ngIf="errorCount > 0" class="error">
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* <!-- Error message displayed when the errorCount property on the current context is greater
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* than 0. -->
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* {{errorCount}} errors detected
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* </div>
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* ```
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*
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* ### Syntax
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*
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* - `<div *ngIf="condition">...</div>`
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* - `<div template="ngIf condition">...</div>`
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* - `<template [ngIf]="condition"><div>...</div></template>`
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*
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* @stable
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*/
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@Directive({selector: '[ngIf]', inputs: ['ngIf']})
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export class NgIf {
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private _prevCondition: boolean = null;
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constructor(private _viewContainer: ViewContainerRef, private _templateRef: TemplateRef<Object>) {
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}
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set ngIf(newCondition: any /* boolean */) {
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if (newCondition && (isBlank(this._prevCondition) || !this._prevCondition)) {
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this._prevCondition = true;
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this._viewContainer.createEmbeddedView(this._templateRef);
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} else if (!newCondition && (isBlank(this._prevCondition) || this._prevCondition)) {
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this._prevCondition = false;
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this._viewContainer.clear();
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}
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}
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}
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