lastframe事件在default, normal, reverse的模式下都无法调用。但是在loop，pingpong模式下才能调用，为什么啊？
onPlay:function(event) {
var state=event.detail;
var type =event.type;
console.log(event);
console.log(state);
console.log(type);
},
onLoad: function () {
var anim = this.getComponent(cc.Animation);
anim.play(‘TestAni’);
anim.on(‘lastframe’,this.onPlay,this);
}，