我试图做休闲,但对我来说_renderer.setElementStyle抛出异常.

EXCEPTION: TypeError: Cannot set property ‘background-color’ of
undefined in [null]

指令：

import {Directive,ElementRef,Renderer,OnInit} from 'angular2/core';

@Directive({
    selector: '[highlight-directive]'
})

export class HighlightDirective implements OnInit{
    private _defaultColor= 'green';

    constructor(private _elmRef: ElementRef,private _renderer: Renderer) {}

    ngOnInit(): any {
        this._renderer.setElementStyle(this._elmRef,"background-color",this._defaultColor);
        //this._elmRef.nativeElement.style.backgroundColor = this._defaultColor; //this way works fine.
    }
}

我使用该指令的模板：

template: `
    <div highlight-directive>
        Highlight me
    </div>
    <br>
    <div highlight-directive>
        2 Highlight me 2
    </div>
`,

教师工作区：

任何人都能找到我做错的事吗？

谢谢.