@Viewchild not initializing during ngOnInit

From official docs: https://angular.io/api/core/ViewChild#description

View queries are set before the ngAfterViewInit callback is called.

In order to get @ViewChild property inited, you need to call it in ngAfterViewInit lifecycle hook.

export class MessageComponent implements OnInit, AfterViewInit {

   @ViewChild(MatSort) sort: MatSort;

   ngAfterViewInit(){
      console.log(this.sort)
   }
}

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If you are using Angular 8, you need to refactor the implementation of @ViewChild properties since static flag is required