Angular2: ViewChild Referencing in constructor of class or in class body?

Question

What is best practice and where is the difference between:

export class suchPage {
    @ViewChild(SuchDirective) suchDirective:SuchDirective;
}

and

export class suchPage {
    @ViewChild(SuchDirective);


    constructor(
        private suchDirective:SuchDirective
    ) {}
}

Answer 1

Official documentation references the first method. I'm guessing it's the best practice:

https://angular.io/docs/ts/latest/cookbook/component-communication.html#!#parent-to-view-child

Answer 2

第二种方法不起作用，因为ViewChild注入的元素仅在视图初始化（ ngAfterViewInit ）之后可用。