function PreviousState() {
	this.type=null;
	//当前活动的墙
    this.currentWallId=null;
	this.currentStairId=null;
	//选中的线段所在位置的起始点
    //选中点的位置
    this.currentstartlinePointIndex;
    //选中的线段所在位置的终点
    this.currentendlinePointIndex;
};

PreviousState.prototype.save=function(state)
{
	if(state.selectWallSet!=null)
	{
		this.type=state.selectWallSet.type;
		this.currentWallId=state.currentWallId;
	}
	else if(state.selectStairSet!=null)
	{
		this.type=state.selectStairSet.type;
		this.currentStairId=state.currentStairId;
	}
	else
	{
		this.type=null;
		this.currentStairId=null;
		this.currentWallId=null;
	}
	this.currentstartlinePointIndex=state.currentstartlinePointIndex;
	this.currentendlinePointIndex=state.currentendlinePointIndex;
};