angular2 change detection on resize div

问题:

I use bootstrap for my layout and I need to check if the automatic calculated size of my DIV with bootstrap for example width = 25% is changed.

Is there a possibility to do change detection on a attribute which I don't set in my template, but is set by bootstrap. (window:resize) is not enough.

thx

回答1:

You can add a directive to the div and implement lifecycle hook ngDoCheck() to perform your own change detection logic. You'll need to inject ElementRef:

constructor(private _elRef:ElementRef) {}
ngDoCheck() {
   // use ElementRef to examine the div property of interest

If the div is inside a component template, add a local template variable

<div #myDiv ...>

Then use @ViewChild() to get a reference to the div and implement lifecycle hook ngDoCheck() or ngAfterViewChecked() to perform your own change detection logic.

@ViewChild('myDiv') theDiv:ElementRef;
ngAfterViewChecked() {
   // use this.theDiv to examine the div property of interest

Note that ngDoCheck() and ngAfterViewChecked() will be called every time change detection runs. See also the dev guide Lifecycle Hooks.

回答2:

I have tried the correct answer but the refresh rate wasn't very accurate, So I looked for another solution.

Here it is

// Directive
@Directive({
  selector: '[resize-detector]',
})

public constructor(public element: ElementRef<HTMLElement>) {}

public ngOnInit(): void {
// Call detectResize as whe the element inits the windows resize event most likely won't trigger
  this.detectResize();
}

// if you need the windowDimensions add ", [$event]" to @HostListener and pass event to detectResize(event)
@HostListener('window:resize') 
public detectResize(): void {
  console.log(element.nativeElement.offsetWidth);
  console.log(element.nativeElement.offsetHeight);
  // Do you magic here ...
}

Then you can use it in any element like:

<app-component resize-detector></app-component>

回答3:

I had the same problem so I used the lightweight library called Angular-Resize-Event

https://www.npmjs.com/package/angular-resize-event

<div (resized)="onResized($event)"></div>

After installing it just add this output event to any div which you want to check for size changes.

回答4:

There are few methods to track DOM attribute changes:

• polling i.e. setInterval
• DOM mutation events: DOMAttrModified + propertychange for IE
• implementing MutationObserver