on mat select change code example
Example 1: get value onChange from mat-select angular
<mat-select (selectionChange)="doSomething($event)">
Example 2: mat-select onchange event
<mat-form-field>
<mat-select placeholder="State" (selectionChange)="someMethod($event.value)">
<mat-option *ngFor="let state of states" [value]="state.value">
{{ state.viewValue }}
</mat-option>
</mat-select>
</mat-form-field>