Tips on efficiently utilizing stored information in Ionic and Angular applications

I am facing an issue where I can only access my variable inside the this.storage.get function. How can I retrieve this stored data?

Here is the content of tab2.page.html:


  <ion-toolbar>
    <ion-title>
      Stats
    </ion-title>
  </ion-toolbar>
</ion-header>

<ion-content>

<ion-card>
    <ion-card-header>
    Bar Chart
    </ion-card-header>
    <ion-card-content>
    <canvas #barCanvas></canvas>
    </ion-card-content>
</ion-card>

</ion-content>

And here is the content of tab2.page.ts:


import { Chart } from "chart.js";
import { Storage } from '@ionic/storage';

@Component({
  selector: 'app-tab2',
  templateUrl: 'tab2.page.html',
  styleUrls: ['tab2.page.scss']
})
export class Tab2Page implements OnInit {

  constructor(public storage:Storage) {}

  @ViewChild("barCanvas") barCanvas: ElementRef;

  h: any;
  a: any;
  s: any;
  e: any;
  w: any;

  ngOnInit() {

    this.storage.get('happiness').then( (val) => {
       this.h = val;
       console.log(this.h, val)
    })
    this.storage.get('anger').then( (val) => {
       this.a = val;
       console.log(this.a, val)
    })
    this.storage.get('stress').then( (val) => {
       this.s = val;
       console.log(this.s, val)
    })
    this.storage.get('energy').then( (val) => {
       this.e = val;
       console.log(this.e, val)
    })
    this.storage.get('worry').then( (val) => {
       this.w = val;
       console.log(this.w, val)
    })

    console.log(this.h, this.a, this.s, this.e, this.w)

    this.barChart = new Chart(this.barCanvas.nativeElement, {
      type: "bar",
      data: {
        labels: ["Happiness", "Anger", "Stress", "Energy", "Worry"],
        datasets: [
          {
            label: "% out of 100",
            data: [this.h, this.a, this.s, this.e, this.w],
            backgroundColor: [
              "rgba(255, 99, 132, 0.2)",
              "rgba(54, 162, 235, 0.2)",
              "rgba(255, 206, 86, 0.2)",
              "rgba(75, 192, 192, 0.2)",
              "rgba(153, 102, 255, 0.2)"
            ],
            borderColor: [
              "rgba(255,99,132,1)",
              "rgba(54, 162, 235, 1)",
              "rgba(255, 206, 86, 1)",
              "rgba(75, 192, 192, 1)",
              "rgba(153, 102, 255, 1)"
            ],
            borderWidth: 2
          }
        ]
      },
      options: {
        scales: {
          yAxes: [
            {
              ticks: {
                beginAtZero: true,
                stepSize: 20
              }
            }
          ]
        }
      }
    });
  }
}

Answer №1

We recommend using localStorage in place of Ionic Storage for better performance.

  • To store data, use
    localStorage.setItem('key', value)
  • To retrieve data, use localStorage.getItem('key')

Answer №2

get() method from Ionic storage returns a promise, making the call asynchronous. This can lead to issues when trying to use member variables (this.h and others) for creating a chart, as they may not have been assigned values yet, resulting in the use of undefined or previous values. There are various solutions to this problem, one quick fix being to utilize forkJoin(). You can try the following:

import {Observable} from 'rxjs/Observable';

ngOnInit() {
  Observable.forkJoin(
    {
      happiness: this.storage.get('happiness'),
      anger: this.storage.get('anger'),
      stress: this.storage.get('stress'),
      energy: this.storage.get('energy'),
      worry: this.storage.get('worry')
    }
  )
  .subscribe(result => {
    this.barChart = new Chart(this.barCanvas.nativeElement, {
      type: "bar",
      data: {
        labels: ["Happiness", "Anger", "Stress", "Energy", "Worry"],
        datasets: [
          {
            label: "% out of 100",
            data: [result.happiness, result.anger, result.stress, result.energy, result.worry],
            backgroundColor: [
              "rgba(255, 99, 132, 0.2)",
              "rgba(54, 162, 235, 0.2)",
              "rgba(255, 206, 86, 0.2)",
              "rgba(75, 192, 192, 0.2)",
              "rgba(153, 102, 255, 0.2)"
            ],
            borderColor: [
              "rgba(255,99,132,1)",
              "rgba(54, 162, 235, 1)",
              "rgba(255, 206, 86, 1)",
              "rgba(75, 192, 192, 1)",
              "rgba(153, 102, 255, 1)"
            ],
            borderWidth: 2
          }
        ]
      },
      options: {
        scales: {
          yAxes: [
            {
              ticks: {
                beginAtZero: true,
                stepSize: 20
              }
            }
          ]
        }
      }
    });
  });
}

Answer №3

Consider refactoring your approach to executing the barChart only after completing iteration through the storage and retrieving all values.

Instead of directly looping through the storage, you can utilize the forEach iterator method, which returns a Promise upon completion of all iterations:

ngOnInit() {

    this.storage.forEach((value, key) => {

        switch(key) {
            case "happiness":
                this.h = value;
                break;
            case "anger":
                this.a = value;
                break;
            case "stress":
                this.s = value;
                break;
            default:
                console.log('no case matched')
                break;
        }

    }).then(() => {

        this.barChart = new Chart(this.barCanvas.nativeElement, {
            type: "bar",
            data: {
              labels: ["Happiness", "Anger", "Stress", "Energy", "Worry"],
              datasets: [
                {
                  label: "% out of 100",
                  data: [this.h, this.a, this.s, this.e, this.w],
                  backgroundColor: [
                    "rgba(255, 99, 132, 0.2)",
                    "rgba(54, 162, 235, 0.2)",
                    "rgba(255, 206, 86, 0.2)",
                    "rgba(75, 192, 192, 0.2)",
                    "rgba(153, 102, 255, 0.2)"
                  ],
                  borderColor: [
                    "rgba(255,99,132,1)",
                    "rgba(54, 162, 235, 1)",
                    "rgba(255, 206, 86, 1)",
                    "rgba(75, 192, 192, 1)",
                    "rgba(153, 102, 255, 1)"
                  ],
                  borderWidth: 2
                }
              ]
            },
            options: {
              scales: {
                yAxes: [
                  {
                    ticks: {
                      beginAtZero: true,
                      stepSize: 20
                    }
                  }
                ]
              }
            }
        });

    })
}

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