How to bind to model with Angular Material <mat-button-toggle>?

public selectedVal: string;
constructor() { }

ngOnInit(){
  this.selectedVal ='option1';
} 

public onValChange(val: string) {
  this.selectedVal = val;
}

 <mat-button-toggle-group #group="matButtonToggleGroup" [value]="selectedVal" (change)="onValChange(group.value)" >
  <mat-button-toggle value="option1">
    Option 1
  </mat-button-toggle>
  <mat-button-toggle value="option2">
    Option 2
  </mat-button-toggle>
</mat-button-toggle-group>

If you are trying to use mat-button-toggle to switch between enabling / disabling something, you will have to use a binding on mat-button-toggle-group, and make sure that the mat-button-toggle's themselves have the boolean values of true and false, not the string values. That is to say:

<mat-button-toggle-group [(ngModel)]="isEnabled">
    <mat-button-toggle [value]="true"> Enable </mat-button-toggle>
    <mat-button-toggle [value]="false"> Disable </mat-button-toggle>
</mat-button-toggle-group>

MatButtonToggle component doesn't implement ControlValueAccessor therefore you can't use ngModel on it. ngDefaultControl was introduced for other purposes.

MatButtonToggle is supposed to be a part of mat-button-toggle-group. But if you want to use it as a standalone component and bind model to it here is some example of how you can do it:

<mat-button-toggle 
  [checked]="myFlagForButtonToggle" 
  (change)="myFlagForButtonToggle = $event.source.checked">
    Toggle me!
</mat-button-toggle>

Plunker Example

mat-button-toggle dont have a boolean value and [(ngModel)] won't work. See doc.

These toggles can be configured to behave as either radio-buttons or checkboxes.

a use case may be like this

<mat-button-toggle-group  [(ngModel)]="myFlagForButtonToggle">
  <mat-button-toggle value="button1"  ngDefaultControl>Toggle me!</mat-button-toggle>
  <mat-button-toggle value="button2"  ngDefaultControl>Toggle me!</mat-button-toggle>
  <mat-button-toggle value="button3"  ngDefaultControl>Toggle me!</mat-button-toggle>
</mat-button-toggle-group>

and change your boolean to myFlagForButtonToggle :string;