Flash/Flex学习笔记(30)：不用startDrag和stopDrag的对象拖动

对于从Sprite类继承来的对象，要实现拖放当然是Flash/Flex学习笔记(13)：对象拖动(startDrag/stopDrag) 里讲的方法最方便，但是对于不是从Sprite类继承得来的对象，这startDrag/stopDrag是不能用的，这时候只能采用最通常用做法：利用Mouse_Down,Mouse_UP,Mouse_Move事件来处理

注意：对象的Mouse_Move事件，只有当鼠标在对象上时才能被监听，如果用户鼠标移动过快，超出了对象的范围，该事件就不起作用了，所以监听Mouse_Move事件时，应该监听stage对象的Mouse_Move事件，而非对象本身的（详情见下面的代码）

package {
	import flash.display.Sprite;
	import flash.events.MouseEvent;
	import flash.ui.MouseCursor;
	import flash.ui.Mouse;

	public class MouseMoveDrag extends Sprite {

		private var offsetX:Number;
		private var offsetY:Number;
		private var arrBalls:Array;
		private var _draggedBall:Ball;

		public function MouseMoveDrag():void {

			arrBalls=new Array(7);

			for (var i:uint=0; i<arrBalls.length; i++) {
				arrBalls[i]=new Ball(20+Math.random()*30,Math.random()*0xffffff);
				arrBalls[i].x=stage.stageWidth*Math.random();
				arrBalls[i].y=stage.stageHeight*Math.random();
				arrBalls[i].addEventListener(MouseEvent.MOUSE_DOWN, MouseDownHandler);
				arrBalls[i].addEventListener(MouseEvent.MOUSE_UP, MouseUpHandler);
				arrBalls[i].addEventListener(MouseEvent.MOUSE_OVER,MouseOverHandler);
				arrBalls[i].addEventListener(MouseEvent.MOUSE_OUT,MouseOutHandler);
				addChild(arrBalls[i]);
			}

		}

		function MouseOverHandler(e:MouseEvent):void {
			Mouse.cursor=MouseCursor.BUTTON;
		}

		function MouseOutHandler(e:MouseEvent):void {
			Mouse.cursor=MouseCursor.AUTO;
		}

		//开始移动
		function MouseDownHandler(e:MouseEvent):void {
			offsetX=e.localX;
			offsetY=e.localY;
			_draggedBall = e.target as Ball;
			stage.addEventListener(MouseEvent.MOUSE_MOVE, stageMouseMoveHandler);
		}

		//停止拖动
		function MouseUpHandler(e:MouseEvent):void {
			_draggedBall = null;
			//拖动完成后，移除舞台的Mouse_Move监听
			stage.removeEventListener(MouseEvent.MOUSE_MOVE, stageMouseMoveHandler);
		}

		function stageMouseMoveHandler(e:MouseEvent):void {
			//trace(e.target);
			var _ball:Ball=e.target as Ball;
			if (_ball!=null) {
				//设置新的坐标
				_ball.x=mouseX-offsetX;
				_ball.y=mouseY-offsetY;
			}
			else {
				//trace("您拖得太快了!" + _draggedBall.toString());
				if (_draggedBall!=null){
					_draggedBall.x=mouseX-offsetX;
					_draggedBall.y=mouseY-offsetY;
				}
			}
		}

	}
}