angular directive to show a spinner in button

Question

I'm trying to write a directive to modify a button to show a spinner button while a server operation is in progress.

<button type="submit" waitingButton (click)="submit($event)">
 {{submitBtnText}}
</button>

So far, I've been able to show the spinner, but I don't know how to capture the result from the click event to switch it back to normal.

This is the directive:

import {
  Directive,
  ElementRef,
  HostListener,
  OnInit,
  Renderer2,
  ComponentFactoryResolver,
  ViewContainerRef
} from '@angular/core';
import { MatSpinner } from '@angular/material';


@Directive({
  selector: '[bcnWaitingButton]'
})
export class BCNWaitingButtonDirective implements OnInit {


  constructor(
    private el: ElementRef, 
    private renderer: Renderer2, 
    private componentFactoryResolver: ComponentFactoryResolver, 
    public vcRef: ViewContainerRef) {

  }

  ngOnInit(): void {
    
  }

  @HostListener('click', ['$event']) onClick(e): void {
    // Create the spinner
    const factory = this.componentFactoryResolver.resolveComponentFactory(MatSpinner);
    const componentRef = this.vcRef.createComponent(factory);
    const spinner: MatSpinner = componentRef.instance;
    
    // Configure the spinner
    spinner.strokeWidth = 3;
    spinner.diameter = 24;

    // Set the button to disabled
    this.renderer.setAttribute(this.el.nativeElement, 'disabled', 'true');
    
    // Apply new styles
    const span: ElementRef = this.el.nativeElement.querySelector('.mat-button-wrapper');
    this.renderer.setStyle(span, 'display', 'flex');
    this.renderer.setStyle(span, 'align-items', 'center');
    this.renderer.setStyle(span, 'justify-content', 'center');
    this.renderer.setStyle(spinner._elementRef.nativeElement, 'margin-top', '0px');
    this.renderer.setStyle(spinner._elementRef.nativeElement, 'margin-left', '5px');

    // Append the spinner
    this.renderer.appendChild(this.el.nativeElement.firstChild, spinner._elementRef.nativeElement);
  }
}

Any ideas on how to do that? Should I have an @Input with the submit callback so I can call it from the onClick function of the directive?

Answer 1

Here is a full working directive for replacing a Material button's text with a MatSpinner and then back to the text when the operation is complete. It utilizes parts of the first two answers:

import {
  ComponentFactoryResolver, Directive, Input, OnChanges, OnInit, Renderer2, SimpleChanges, ViewContainerRef
} from '@angular/core';
import { ElementRef } from '@angular/core';
import { MatSpinner } from '@angular/material';

@Directive({
  selector: 'button[appShowSpinner]'
})
export class SpinnerButtonDirective implements OnInit, OnChanges {
  // tslint:disable-next-line:no-input-rename
  @Input('appShowSpinner') showSpinner: boolean;
  originalInnerText: string;
  spinner: MatSpinner;

  constructor(
    private el: ElementRef,
    private renderer: Renderer2,
    private viewContainerRef: ViewContainerRef,
    private componentFactoryResolver: ComponentFactoryResolver
  ) { }

  ngOnInit() {
    // Record the button's original text
    this.originalInnerText = this.el.nativeElement.innerText;

    // Set the button to maintain the same dimensions, even once we put the spinner inside.
    this.el.nativeElement.style.width = `${(this.el.nativeElement as HTMLElement).offsetWidth}px`;
    this.el.nativeElement.style.height = `${(this.el.nativeElement as HTMLElement).offsetHeight}px`;

    // Create the spinner
    const factory = this.componentFactoryResolver.resolveComponentFactory(MatSpinner);
    const componentRef = this.viewContainerRef.createComponent(factory);
    this.spinner = componentRef.instance;

    // Configure the spinner
    this.spinner.strokeWidth = 3;
    this.spinner.diameter = 24;

    // Hide the spinner
    this.renderer.setStyle(this.spinner._elementRef.nativeElement, 'display', 'none');

    // Apply new styles to the button content's container
    const span = this.el.nativeElement.querySelector('.mat-button-wrapper') as HTMLSpanElement;
    this.renderer.setStyle(span, 'display', 'flex');
    this.renderer.setStyle(span, 'align-items', 'center');
    this.renderer.setStyle(span, 'justify-content', 'center');
  }

  ngOnChanges(changes: SimpleChanges) {
    if (typeof(changes.showSpinner) === 'object' && !changes.showSpinner.isFirstChange()) {
      if (changes.showSpinner.currentValue === true) {
        // Clear the button's text
        const span = this.el.nativeElement.querySelector('.mat-button-wrapper') as HTMLSpanElement;
        span.innerText = '';

        // Append the spinner
        this.renderer.appendChild(this.el.nativeElement.firstChild, this.spinner._elementRef.nativeElement);

        // Show the spinner
        this.renderer.setStyle(this.spinner._elementRef.nativeElement, 'display', 'inherit');
      }

      if (changes.showSpinner.currentValue === false) {
        // Hide the spinner
        this.renderer.setStyle(this.spinner._elementRef.nativeElement, 'display', 'none');

        // Remove the spinner
        this.renderer.removeChild(this.el.nativeElement.firstChild, this.spinner._elementRef.nativeElement);

        const span = this.el.nativeElement.querySelector('.mat-button-wrapper') as HTMLSpanElement;
        span.innerText = this.originalInnerText;
      }

      this.el.nativeElement.disabled = changes.showSpinner.currentValue;
    }
  }
}

Using the directive:

<button [appShowSpinner]="isSaving" mat-raised-button>
  Submit
</button>