angular5 子組件監聽父組件傳入值的變化方法

import {
Component,
Input,
OnChanges,
SimpleChanges
} from '@angular/core';
import {
NavController
} from 'ionic-angular';
 
@Component({
selector: 'cs-img-lazy',
templateUrl: 'cs-img-lazy.html'
})
export class CsImgLazyComponent implements OnChanges {
 
@Input() default: string; 
@Input() src: string 
 
constructor(public navCtrl: NavController) {
 
}
 
ngOnInit() {
}
 
ngOnChanges(changes: SimpleChanges) {
 console.log('ngOnChanges', this.src);
 this.loadImage(this.src, () => {
 this.default = this.src;
 });
}
 
loadImage(url, callback) {
var img = new Image();
img.onload = () => {
if (img.complete) {
img.onload = null
callback(img);
return;
}
}
img.src = url;
}

}