在Angular2中对* ngFor的承诺

Question

i'm using angular2 and i'm trying to get the .style.width attribute from an element which is loaded inside a *ngFor - loop. I want to use it to define the width of some other elements. This should be done while the page loads. I dont want to store the width as some var inside my code. I want to get it directly from the dom.

promise :

let kistenPromise = new Promise(function(resolve, reject){

            let itemListContainer = document.getElementById("itemContainer");

                if(itemListContainer.children[0] != undefined){
                    resolve(itemListContainer.children);    
                }else{
                    reject(Error("Promise was not fullfilled!"));
                }
}.bind(this));

handler:

kistenPromise.then(
        function(result){
            console.log(result);
        }.bind(this), function(err){
            console.log(err);
        }.bind(this));

html:

<div class="itemFrame" id="itemContainer">
        <div class="listStyle" *ngFor="let item of list">{{item}}</div>
</div>

When i use the colde like this it only returns the Promise was not fullfilled .

However if i try itemList.children != undefined and return the .length it will return 0.What am i missing?

Thanks in advance!

Answer 1

getElementById returns a single element, because id should be unique, and not an array. Other queries do return and array (for example getElementsByClassName or getElementsByTagName ).

Answer 2

Where is your handler written? It may be getting executed before the view is even initialized. If so, try moving it to ngAfterViewInit

your.component.ts

import { AfterViewInit } from '@angular/core'
export class YourComponent implements AfterViewInit {

    ngAfterViewInit() {
        kistenPromise.then(...)

    }
}

Answer 3

You may want to use AfterViewInit . Add a local variable #itemContainer to your container:

<div class="itemFrame" id="itemContainer" #itemContainer>
    <div class="listStyle" *ngFor="let item of list">{{item}}</div>
</div>

Then in your component you can check the element for children (or pass the element to another function that checks for it):

import { ViewChild, ElementRef, AfterViewInit } from '@angular/core';

export class YourComponent implements AfterViewInit {
  @ViewChild('itemContainer') itemContainer: ElementRef;

  ngAfterViewInit() {
      if (this.itemContainer.nativeElement.children.length) {
          // ...
      } else {
          // ...
      }
  }
}