最終效果：

一樓的代碼有個問題：就是向右下角拉的時候鼠標會在矩形框右下角的頂點上。下面的代碼可以解決此問題：

package {
 import flash.display.Sprite;
 import flash.events.MouseEvent;
 public class select extends Sprite {
  public var MouseStart:Array;
  public var SelectSprite:Sprite;
  public var FirstSelect:Boolean;
  public function select():void {
   stage.addEventListener(MouseEvent.MOUSE_DOWN,selectstart);
  }
  public function selectstart(event:MouseEvent):void {
   FirstSelect=true;
   MouseStart=[event.stageX,event.stageY];
   stage.addEventListener(MouseEvent.MOUSE_MOVE,selecting);
   stage.addEventListener(MouseEvent.MOUSE_UP,selectend);
  }
  public function selecting(event:MouseEvent):void {
   if (!FirstSelect) this.removeChild(SelectSprite); //清除以前的選擇框
   FirstSelect=false;
   var ax:int=MouseStart[0];
   var ay:int=MouseStart[1];
   var aw:int=event.stageX-ax;
   var ah:int=event.stageY-ay;
   
   SelectSprite=new Sprite();
   SelectSprite.graphics.beginFill(0x3399ff,0.4);
   SelectSprite.graphics.lineStyle(1,0x3399ff);
   SelectSprite.graphics.drawRect(ax-1,ay-1,aw,ah);
   SelectSprite.graphics.endFill();
   this.addChild(SelectSprite);
  }
  public function selectend(event:MouseEvent):void {
   stage.removeEventListener(MouseEvent.MOUSE_MOVE,selecting);
   stage.removeEventListener(MouseEvent.MOUSE_UP,selectend);
   if (!FirstSelect) this.removeChild(SelectSprite);
  }
 }
}

SelectSprite.graphics.drawRect(ax-1,ay-1,aw,ah);
這樣就和win7系統下基本上一樣了

回覆：5樓

應該可以通過改繼承的方法實現