Flash/Flex学习笔记(31)：对象拖拽与投掷

对象拖拽：

这其实就是以前所学知识：Flash/Flex学习笔记(13)：对象拖动(startDrag/stopDrag) + Flash/Flex学习笔记(23)：运动学原理 的综合运用，要提一下的是下面代码中对于EnterFrame的添加与移除操作

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package {

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import flash.display.Sprite;

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import flash.display.StageAlign;

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import flash.display.StageScaleMode;

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import flash.events.Event;

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import flash.events.MouseEvent;

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import flash.ui.Mouse;

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import flash.ui.MouseCursor;

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public class Bouncing2 extends Sprite {

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private var ball:Ball;

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private var vx:Number;

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private var vy:Number;

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private var bounce:Number=-0.8;//反弹速度百分比

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private var gravity:Number=0.9;//重力加速度百分比

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private var frictionX:Number=0.98;//摩擦力因子--水平方向

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private var frictionY:Number=0.99;//摩擦力因子--垂直方向

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public function Bouncing2() {

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init();

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}

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private function init():void {

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stage.scaleMode=StageScaleMode.NO_SCALE;

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stage.align=StageAlign.TOP_LEFT;

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ball=new Ball(20)  ;

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ball.x=stage.stageWidth/2;

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ball.y=stage.stageHeight/2;

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vx=(Math.random()*2-1) * 20;

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vy=-10;

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addChild(ball);

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ball.addEventListener(MouseEvent.MOUSE_DOWN,MouseDownHandler);

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ball.addEventListener(MouseEvent.MOUSE_OVER,function(){ Mouse.cursor = MouseCursor.HAND;});

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ball.addEventListener(MouseEvent.MOUSE_OUT,function(){ Mouse.cursor = MouseCursor.AUTO;});

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addEventListener(Event.ENTER_FRAME,EnterFrameHandler);

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}

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private function EnterFrameHandler(event:Event):void {

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vy+=gravity; //加入重力加速度，所以肯定会向下掉

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vx *= frictionX; //加入摩擦力，所以最终会停下来

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vy *= frictionY;

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ball.x+=vx;//产生移动

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ball.y+=vy;

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var left:Number=0;

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var right:Number=stage.stageWidth;

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var top:Number=0;

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var bottom:Number=stage.stageHeight;

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//水平方向边界检测

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if (ball.x+ball.radius>right) {

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ball.x=right-ball.radius;

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vx*=bounce;

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} else if (ball.x - ball.radius < left) {

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ball.x=left+ball.radius;

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vx*=bounce;

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}

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//垂直方向边界检测

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if (ball.y+ball.radius>bottom) {

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ball.y=bottom-ball.radius;

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vy*=bounce;

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} else if (ball.y - ball.radius < top) {

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ball.y=top+ball.radius;

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vy*=bounce;

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}

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}

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private function MouseDownHandler(e:MouseEvent):void {

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stage.addEventListener(MouseEvent.MOUSE_UP,MouseUpHandler);

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ball.startDrag();

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removeEventListener(Event.ENTER_FRAME,EnterFrameHandler);//移除EnterFrame事件，否则在拖动过程中，小球还在不断下掉

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}

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private function MouseUpHandler(e:MouseEvent):void {

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stage.removeEventListener(MouseEvent.MOUSE_UP,MouseUpHandler);

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ball.stopDrag();

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addEventListener(Event.ENTER_FRAME,EnterFrameHandler);//拖动完成后，恢复EnterFrame事件监听，以便小球能不断运动

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}

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}

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}

对象投掷：

在上面的代码中，鼠标的拖拽只影响了小球的y坐标(注：指对运动方面的影响)，即仅相当于举高了小球。而投掷则意味着：在鼠标松开小球的那一瞬间，小球也应该具备有一定的出口速度(即鼠标最终的移动速度)。Flash中每一帧对应的时间基本上是相同的，可以认为这就是物理中的“单位时间”，根据刚才对投掷概念的理解，只要代码能得知在鼠标松开小球的最后一帧，小球在x,y轴方向的位移，即为小球的出口x,y轴速度.

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package {

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import flash.display.Sprite;

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import flash.display.StageAlign;

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import flash.display.StageScaleMode;

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import flash.events.Event;

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import flash.events.MouseEvent;

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import flash.ui.MouseCursor;

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import flash.ui.Mouse;

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public class Throwing extends Sprite {

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private var ball:Ball;

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private var vx:Number;

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private var vy:Number;

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private var bounce:Number=-0.8;

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private var gravity:Number=0.75;

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private var frictionX:Number = 0.98;

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private var frictionY:Number = 0.99;

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private var oldX:Number;

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private var oldY:Number;

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public function Throwing() {

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init();

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}

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private function init():void {

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stage.scaleMode=StageScaleMode.NO_SCALE;

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stage.align=StageAlign.TOP_LEFT;

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ball = new Ball(30);

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ball.x = stage.stageWidth/2;

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ball.y = stage.stageHeight/2;

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vx = Math.random()*10-5;

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vy = -10;

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addChild(ball);

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ball.addEventListener(MouseEvent.MOUSE_DOWN, MouseDownHandler);

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ball.addEventListener(MouseEvent.MOUSE_OVER,function(){Mouse.cursor = MouseCursor.HAND;});

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ball.addEventListener(MouseEvent.MOUSE_OUT,function(){Mouse.cursor = MouseCursor.AUTO;});

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addEventListener(Event.ENTER_FRAME, EnterFrameHandler);

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}

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private function MouseDownHandler(event:MouseEvent):void {

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oldX = ball.x;

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oldY = ball.y;

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stage.addEventListener(MouseEvent.MOUSE_UP, MouseUpHandler);

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ball.startDrag();

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removeEventListener(Event.ENTER_FRAME, EnterFrameHandler);

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addEventListener(Event.ENTER_FRAME, TrackVelocity);

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}

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private function EnterFrameHandler(event:Event):void {

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vy += gravity;

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vx *= frictionX;

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vy *= frictionY;

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ball.x += vx;

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ball.y += vy;

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var left:Number=0;

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var right:Number=stage.stageWidth;

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var top:Number=0;

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var bottom:Number=stage.stageHeight;

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if (ball.x+ball.radius>right) {

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ball.x=right-ball.radius;

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vx*=bounce;

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} else if (ball.x - ball.radius < left) {

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ball.x=left+ball.radius;

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vx*=bounce;

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}

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if (ball.y+ball.radius>bottom) {

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ball.y=bottom-ball.radius;

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vy*=bounce;

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} else if (ball.y - ball.radius < top) {

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ball.y=top+ball.radius;

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vy*=bounce;

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}

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}

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//跟踪每一帧小球的速度(坐标位置)

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private function TrackVelocity(event:Event):void {

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vx = ball.x-oldX;

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vy = ball.y-oldY;

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oldX = ball.x;

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oldY = ball.y;

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}

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private function MouseUpHandler(e:MouseEvent):void {

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stage.removeEventListener(MouseEvent.MOUSE_UP, MouseUpHandler);

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ball.stopDrag();

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removeEventListener(Event.ENTER_FRAME, TrackVelocity);

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addEventListener(Event.ENTER_FRAME, EnterFrameHandler);

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}

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}

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}