Components: <mat-checkbox> class not updating to ng-invalid

[gauravsoni1]

Bug, feature request, or proposal:

The first time the component loads , the class is ng-invalid , if i check and uncheck the checkbox. The class does not update to ng-invalid.
I am using the reactive form.
I have set the Validators.required for this componenet

What is the expected behavior?

Class should update to ng-invalid

What is the current behavior?

Class is ng-valid , even though it should be ng-invalid

What are the steps to reproduce?

Providing a StackBlitz reproduction is the best way to share your issue.

StackBlitz starter: https://goo.gl/wwnhMV

StackBlitz - https://stackblitz.com/edit/angular-material2-issue-jlarze

What is the use-case or motivation for changing an existing behavior?

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

"@angular/material": "^5.2.0"

Is there anything else we should know?

[tinayuangao]

@gauravsoni1 Could you please provide a StackBlitz reproduction?

[gauravsoni1]

@tinayuangao - added Stackblitz to the issue.

[tinayuangao]

@gauravsoni1
See https://stackblitz.com/edit/angular-material2-issue-ftuvb7?file=app/app.component.ts

If you use Validators.required the form control will be valid when the checkbox value is false (the value when you uncheck the checkbox). This is because false is still a valid answer.

Use Validators.requireTrue to make form control invalid when checkbox is false.

[zencakd]

Validators.requireTrue works but it necessary to alter the class manually to render the checkbox as invalid in html. Should not checkbox behave in the same way as invalid input?

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