Ionic 2 header shrink

shrink.ts

import {ViewChild, Injectable} from "@angular/core";
import {Platform} from 'ionic-angular';
@Injectable()
export class Shrink {
    scrollPosition: number = 0;
    lastScrollTop: number = 0;
    style: any;
    height: number;

    constructor(private platform: Platform) {

        this.platform = platform;
        if (this.platform.is('ios')) {
            this.height = 44;
        } else {
            //android
            this.height = 56;
        }

    }

    returnStyle() {
        return this.style;
    }
    init(content) {
        content.addScrollListener((event) => {
            this.scrollPosition = event.target.scrollTop;
            if (this.scrollPosition > this.lastScrollTop && this.scrollPosition >= 5) {
                // Scrolling Down
                this.style = { 'transform': 'translateY(-' + this.height + 'px)', 'transition': 'all 0.3s linear' }
            }
            else {
                // Scrolling up
                this.style = { 'transform': 'translateY(0px)', 'transition': 'all 0.3s linear' }
            }
            this.lastScrollTop = this.scrollPosition;
        });
    }
}