Angular 2 does not update the variable value within a dataservice call on the page until you navigate away from the page and then come back to it

Currently, I am working with Angular2 and have encountered a strange issue. I have a variable that I display on the page, and when a button is clicked, a data service is called to update the value of this variable. Surprisingly, even after changing the value within the dataservice call, the updated value is not reflected on the page until I navigate away from the page and back again. Any modifications made to the variable outside of the dataservice call are immediately displayed. Here's a snippet of the code:

HTML template:

<button type="button" class="btn (click)="clickNextButton()">
    <span>save</span>  
</button>

{{text}}

Typescript class

export class ConfigComponent implements OnInit {
    public text = '';

    ..
    ..
    private clickNextButton(): void {
        this.text = 'abc';
        this.dataService.getConfig()
            .then((config: IConfig): void => {
            console.log('printed');
            this.text = 'xyz';
            console.log('printed..');
        });
    }
}

After clicking the button, the text changes to 'abc' as expected, but it does not update to 'xyz'. Despite logging in the console showing that the code is being executed correctly, the variable change inside the dataservice call is not reflecting on the page. Can anyone suggest how to resolve this issue?

Update:

This problem seems to occur only when the component is nested within another component, like so:

 <prod-setup
     ....
 </prod-setup>   

When I update a variable value within the dataservice call of the main component, it works fine and displays the new value. However, if the variable is updated within the dataservice call of the included component, the change is not reflected on the UI. Any insights or solutions to this scenario would be greatly appreciated.

Answer №1

It is possible that your asynchronous call is not being triggered to update the UI because it is outside of the ngZone. Angular optimizes performance by running async calls outside of zone detection. To ensure proper UI updates, you can place your code inside the ngZone:

import {NgZone} from '@angular/core';

export class ConfigComponent implements OnInit {
    public text = '';
    public constructor(private ngZone: NgZone) { }

    ..
    ..
    private clickNextButton(): void {
        this.text = 'abc;
        this.ngZone.run(() => {
            this.dataService.getConfig()
                .then((config: IConfig): void => {
                console.log('printed');               
                this.text = 'xyz';                             
                console.log('printed..');
            });
        });
    }
}

Answer №2

Utilizing resolve() also enables the calling function to receive a notification and execute any necessary post-processing tasks.

private clickNextButton(): void {
        this.text = 'abc;
        this.dataService.getConfig()
            .then((config: IConfig): void => {
            console.log('printed');
            this.text = 'xyz';
            this.text = resolve();     

        });
    }

An alternative approach could involve invoking another function that will handle setting the value.

     private clickNextButton(): void {
        this.text = 'abc;
        this.dataService.getConfig()
            .then((config: IConfig): void => {
            console.log('printed');
            this.text = 'xyz';
            this.text = resolve('xyz');
            this.setValue();     

        });
    }
    setValue(): void{
        this.text
    }

Answer №3

Is the data service's text going out of its scope? For example: private clickNextButton =(): void => { It could also set up a message service that sends a message to the component when updated.

Angular 4 service error: 'newService' property undefined

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