最近做的东西，对于效果编程比较多，特别是缓冲，加速度等效果，特意研讨了一下Tween类，写篇教程分享

给大家，算是过年送给大家的新年礼物！

下面是官方写的fl.transitions.Tween类：
可以先尝试看一下这段代码的写法，用这个方法去看：
从结构函数看起，假设我使用了该类
new Tween(mc,"x",Regular.easeOut,0,200,4);
结合adobe的协助文档，当初始化实例的时候，便对对象mc的x进行Regular.easeOut操作，具体是从0值到200

值，历时4帧
然后问一个为什么，他为什么会对对象mc的x进行Regular.easeOut操作，具体是从0值到200值，历时4帧？
带着这个问题，如今开始看这个类吧！从结构函数看
package fl.transitions
{
import flash.events.*;
import flash.display.*;
import flash.utils.*;
[Event(name="motionChange", type="fl.transitions.TweenEvent")]
[Event(name="motionFinish", type="fl.transitions.TweenEvent")]
[Event(name="motionLoop", type="fl.transitions.TweenEvent")]
[Event(name="motionResume", type="fl.transitions.TweenEvent")]
[Event(name="motionStart", type="fl.transitions.TweenEvent")]
[Event(name="motionStop", type="fl.transitions.TweenEvent")]
public class Tween extends EventDispatcher
{
   protected static var _mc:MovieClip = new MovieClip();

  public var isPlaying:Boolean = false;

   public var obj:Object = null;

  public var prop:String = "";

  public var func:Function = function (t:Number, b:Number, c:Number, d:Number):Number { return

c*t/d + b; }

  public var begin:Number = NaN;

  public var change:Number = NaN;

  public var useSeconds:Boolean = false;

  public var prevTime:Number = NaN;

  public var prevPos:Number = NaN;

  public var looping:Boolean = false;

  private var _duration:Number = NaN;

  private var _time:Number = NaN;

  private var _fps:Number = NaN;

  private var _position:Number = NaN;

  private var _startTime:Number = NaN;

  private var _intervalID:uint = 0;

  private var _finish:Number = NaN;

  private var _timer:Timer = null;

 public function get time():Number
 {
 return this._time;
 }

  public function set time(t:Number):void
  {
    this.prevTime = this._time;
    if (t > this.duration) {
      if (this.looping) {
        this.rewind (t - this._duration);
        this.update();
        this.dispatchEvent(new TweenEvent(TweenEvent.MOTION_LOOP, this._time, this._position));
      } else {
        if (this.useSeconds) {
          this._time = this._duration;
          this.update();
        }
        this.stop();
        this.dispatchEvent(new TweenEvent(TweenEvent.MOTION_FINISH, this._time,

this._position));
      }
    } else if (t < 0) {
      this.rewind();
      this.update();
    } else {
      this._time = t;
      this.update();
    }
  }

 public function get duration():Number
 {
 return this._duration;
 }
 
  public function set duration(d:Number):void
  {
    this._duration = (d <= 0) ? Infinity : d;
  }

 public function get FPS():Number
 {
 return this._fps;
 }
 
&nbs