Flash/Flex学习笔记(27)：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
package {
?import flash.display.Sprite;
import flash.display.StageAlign;
import flash.display.StageScaleMode;
?import flash.events.Event;
import flash.events.MouseEvent;
?import flash.ui.Mouse;
import flash.ui.MouseCursor;
?public class Bouncing2 extends Sprite {
private var ball:Ball;
private var vx:Number;
private var vy:Number;
private var bounce:Number=-0.8;//反弹速度百分比
private var gravity:Number=0.9;//重力加速度百分比
?private var frictionX:Number=0.98;//摩擦力因子--水平方向
?private var frictionY:Number=0.99;//摩擦力因子--垂直方向
?public function Bouncing2() {
?init();
?}
?private function init():void {
?stage.scaleMode=StageScaleMode.NO_SCALE;
stage.align=StageAlign.TOP_LEFT;
ball=new Ball(20)? ;
ball.x=stage.stageWidth/2;
ball.y=stage.stageHeight/2;
vx=(Math.random()*2-1) * 20;
?vy=-10;
?addChild(ball);
?ball.addEventListener(MouseEvent.MOUSE_DOWN,MouseDownHandler);
ball.addEventListener(MouseEvent.MOUSE_OVER,function(){ Mouse.cursor = MouseCursor.HAND;});
?ball.addEventListener(MouseEvent.MOUSE_OUT,function(){ Mouse.cursor = MouseCursor.AUTO;});
addEventListener(Event.ENTER_FRAME,EnterFrameHandler);
}
private function EnterFrameHandler(event:Event):void {
vy+=gravity; //加入重力加速度，所以肯定会向下掉
?vx *= frictionX; //加入摩擦力，所以最终会停下来
vy *= frictionY;
ball.x+=vx;//产生移动
ball.y+=vy;
var left:Number=0;
?var right:Number=stage.stageWidth;
?var top:Number=0;
?var bottom:Number=stage.stageHeight;
//水平方向边界检测
if (ball.x+ball.radius>right) {
?ball.x=right-ball.radius;
?vx*=bounce;
?} else if (ball.x - ball.radius < left) {
?ball.x=left+ball.radius;
vx*=bounce;
?}
//垂直方向边界检测
if (ball.y+ball.radius>bottom) {
?ball.y=bottom-ball.radius;
?vy*=bounce;
?} else if (ball.y - ball.radius < top) {
ball.y=top+ball.radius;
?vy*=bounce;
}
}
?private function MouseDownHandler(e:MouseEvent):void {
?stage.addEventListener(MouseEvent.MOUSE_UP,MouseUpHandler);
?ball.startDrag();
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
}
private function MouseUpHandler(e:MouseEvent):void {
?stage.removeEventListener(MouseEvent.MOUSE_UP,MouseUpHandler);
?ball.stopDrag();
?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
?}
}
}
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.
?package {
import flash.display.Sprite;
?import flash.display.StageAlign;
?import flash.display.StageScaleMode;
?import flash.events.Event;
?import flash.events.MouseEvent;
?import flash.ui.MouseCursor;
?import flash.ui.Mouse;
?public class Throwing extends Sprite {
?private var ball:Ball;
?private var vx:Number;
?private var vy:Number;
?private var bounce:Number=-0.8;
private var gravity:Number=0.75;
?private var frictionX:Number = 0.98;
?private var frictionY:Number = 0.99;
?private var oldX:Number;
?private var oldY:Number;
?public function Throwing() {
?
init();
}
private function init():void {
?stage.scaleMode=StageScaleMode.NO_SCALE;
?stage.align=StageAlign.TOP_LEFT;
ball = new Ball(30);
?ball.x = stage.stageWidth/2;
?ball.y = stage.stageHeight/2;
?vx = Math.random()*10-5;
?vy = -10;
?addChild(ball);
ball.addEventListener(MouseEvent.MOUSE_DOWN, MouseDownHandler);
?ball.addEventListener(MouseEvent.MOUSE_OVER,function(){Mouse.cursor = MouseCursor.HAND;});
?ball.addEventListener(MouseEvent.MOUSE_OUT,function(){Mouse.cursor = MouseCursor.AUTO;});
?addEventListener(Event.ENTER_FRAME, EnterFrameHandler);
}
?private function MouseDownHandler(event:MouseEvent):void {
oldX = ball.x;
?oldY = ball.y;
?stage.addEventListener(MouseEvent.MOUSE_UP, MouseUpHandler);
?ball.startDrag();
removeEventListener(Event.ENTER_FRAME, EnterFrameHandler);
addEventListener(Event.ENTER_FRAME, TrackVelocity);
?}
private function EnterFrameHandler(event:Event):void {
vy += gravity;
?vx *= frictionX;
?vy *= frictionY;
?ball.x += vx;
?ball.y += vy;
?var left:Number=0;
var right:Number=stage.stageWidth;
?var top:Number=0;
?var bottom:Number=stage.stageHeight;
?if (ball.x+ball.radius>right) {
?ball.x=right-ball.radius;
?vx*=bounce;
?} else if (ball.x - ball.radius < left) {
?ball.x=left+ball.radius;
?vx*=bounce;
?}
?if (ball.y+ball.radius>bottom) {
?ball.y=bottom-ball.radius;
?vy*=bounce;
?} else if (ball.y - ball.radius < top) {
?ball.y=top+ball.radius;
?vy*=bounce;
?}
?}
?//跟踪每一帧小球的速度(坐标位置) private function TrackVelocity(event:Event):void {
?vx = ball.x-oldX;
?vy = ball.y-oldY;
?oldX = ball.x;
oldY = ball.y;
?}
?private function MouseUpHandler(e:MouseEvent):void {
?stage.removeEventListener(MouseEvent.MOUSE_UP, MouseUpHandler);
ball.stopDrag();
?removeEventListener(Event.ENTER_FRAME, TrackVelocity);
?addEventListener(Event.ENTER_FRAME, EnterFrameHandler);
?}
}
}
