[]Laya.timer.loop调用后出现Cannot read property 'loop' of null

Laya.timer.loop(100,this,function():void{trace(90890789078);});

报错：
Uncaught TypeError: Cannot read property 'loop' of null
at new LayaUISample (LayaUISample.max.js:394)
at LayaUISample.max.js:29731
at LayaUISample.max.js:29733