Ionic 2 with promise doesn't refresh the view correctly


It seems that the application doesn’t refresh for some reason until the next action.
For example:

import {Component} from '@angular/core';
import {SqlStorage} from "ionic-angular";

  templateUrl: 'build/pages/authenticate/authenticate.html'
export class AuthenticatePage {
  private username: string;
  private storage: SqlStorage = null;
  private usernameTemp: string;

  constructor() {


    // = new Storage(SqlStorage); = new SqlStorage();"username", JSON.stringify(this.username));

    let sqlStorage = new SqlStorage();

    sqlStorage.get('username').then((data) => {
      if (data != null){
        this.usernameTemp = JSON.parse(data);
      } else{
        this.usernameTemp = 'fail';

One click that will trigger the showCredentials() function won’t show usernameTemp on screen if the screen has a {{usernameTemp}} section until the second time it is clicked.
It always shows the former value - if you write something and saves it using saveCredentials(), then call showCredentials() then change the value and call saveCredentials(), then call showCredentials() again - you will see the first username, not the second.

Is it possible that happens only to me?
Am I doing something wrong?