How to detect mat-stepper start and end in Angular?

Question

currently, I have a vertical mat-stepper. it fills the steps using a *ngFor.

<mat-step [stepControl]="firstFormGroup" *ngFor="let stream of selectedStreamList; let indexOfelement = index;">

So, I want to detect the start of this stepper and end of this stepper to use as a variable. currently, I'm using a variable as a counter. I increment and decrement it to detect the mat step. but I want a good solution that that. So is there anyone that can help me with this matter?

Answer 1

The mat-stepper emits a selectionChange event every time the step changes. You can subscribe to these changes inside of your typescript file and handle accordingly...something maybe like this.

//app.component.ts

import { Component, ViewChild, AfterViewInit } from "@angular/core";
import { MatStepper } from "@angular/material/stepper";
import { StepperSelectionEvent } from "@angular/cdk/stepper";
import { pluck } from "rxjs/operators";

@Component({
  selector: "app-root",
  template: `
    <mat-vertical-stepper #stepper>
      <mat-step
        *ngFor="let stream of selectedStreamList; let indexOfelement = index"
      ></mat-step>
    </mat-vertical-stepper>
  `
})
export class AppComponent implements AfterViewInit {
  @ViewChild("stepper", { static: false }) private stepper: MatStepper;

  selectedStreamList = [1, 2, 3, 4];
  isAtStart: boolean;
  isAtEnd: boolean;

  constructor() {}

  ngAfterViewInit() {
    this.stepper.selectionChange
      .pipe(pluck("selectedIndex"))
      .subscribe((res: number) => {
        this.isAtStart = res === 0;
        this.isAtEnd = res === this.selectedStreamList.length - 1;
      });
  }
}