1、拖拽，通过 startDrag , stopDrag 来实现。

cir1.addEventListener(MouseEvent.MOUSE_DOWN, onMD);
function onMD(evt) {
cir1.startDrag();
//cir1.addEventListener(MouseEvent.MOUSE_MOVE, onMV);
cir1.addEventListener(MouseEvent.MOUSE_UP, onMU);
}
//function onMV(evt) {
//do something here 
//}
function onMU(evt) {
cir1.stopDrag();
//cir1.removeEventListener(MouseEvent.MOUSE_MOVE, onMV);
cir1.removeEventListener(MouseEvent.MOUSE_UP, onMU);
}

2、碰撞检测，通过 hitTestObject 实现，(尽管都知道碰撞检测的精度是不够用的，但有总比没有好，AS3里还留着)。

if ( cir1.hitTestObject(cir2) ) {  // 两个圆之间的碰撞检测
//do something here
}

3、屏幕中运动的代码段落，碰到屏幕边界后就折返。

cir2.addEventListener(Event.ENTER_FRAME, onEF );
cir2.speed = 10;
cir2.direct = Math.random()*2*Math.PI;
cir2.vx = cir2.speed * Math.cos(cir2.direct);
cir2.vy = cir2.speed * Math.sin(cir2.direct);
cir2.radius = cir2.width/2;
function onEF(evt:Event) { 
cir2.x += cir2.vx;
cir2.y += cir2.vy;
if ( cir2.x – cir2.radius < 0 ){
cir2.x = cir2.radius;
cir2.vx *= -1;
return;
}
if( cir2.x + cir2.radius > stage.stageWidth) {
cir2.x = stage.stageWidth – cir2.radius;
cir2.vx *= -1;
return;
}
if ( cir2.y  – cir2.radius< 0 ){
cir2.y = cir2.radius;
cir2.vy *= -1;
return;
}
if( cir2.y + cir2.radius> stage.stageHeight) {
cir2.y = stage.stageHeight – cir2.radius;
cir2.vy *= -1;
return;
}
}

4、假如 小球2 的运动过程中，每一帧都与小球1 进行碰撞检测，将这部分内容用函数来实现，并且简化处理一下（反弹的角度并不符合物理实验效果），这样的代码合成到一起，实现的效果是：小球1 可以被拖动，小球2 会自动的运动，并且在发生碰撞时会改变方向，碰撞可能发生在墙壁、地板、天花板，还有和第二个小球之间。

function chgPsnBall() {
if ( cir1.hitTestObject(cir2) ) {  
cir2.direct = Math.atan2( cir2.y -cir1.y , cir2.x-cir1.x);
cir2.x += ( cir1.width/2 )* Math.cos( cir2.direct );
cir2.y += ( cir1.width/2 ) * Math.sin( cir2.direct );
cir2.vx = cir2.speed * Math.cos(cir2.direct);
cir2.vy = cir2.speed * Math.sin(cir2.direct);
}
}

场景中建两个小球件元件，实例名为 cir1 和 cir2 ，完整的代码如下：

cir1.addEventListener(MouseEvent.MOUSE_DOWN, onMD);
function onMD(evt) {
cir1.startDrag(); 
cir1.addEventListener(MouseEvent.MOUSE_UP, onMU);
}
function onMU(evt) {
cir1.stopDrag(); 
cir1.removeEventListener(MouseEvent.MOUSE_UP, onMU);
}

function chgPsnBall() {
if ( cir1.hitTestObject(cir2) ) {  
cir2.direct = Math.atan2( cir2.y -cir1.y , cir2.x-cir1.x);
cir2.x += ( cir1.width/2 )* Math.cos( cir2.direct );
cir2.y += ( cir1.width/2 ) * Math.sin( cir2.direct );
cir2.vx = cir2.speed * Math.cos(cir2.direct);
cir2.vy = cir2.speed * Math.sin(cir2.direct);
}
}
cir2.addEventListener(Event.ENTER_FRAME, onEF );
cir2.speed = 10;
cir2.direct = Math.random()*2*Math.PI;
cir2.vx = cir2.speed * Math.cos(cir2.direct);
cir2.vy = cir2.speed * Math.sin(cir2.direct);
cir2.radius = cir2.width/2;
function onEF(evt:Event) {
chgPsnBall();
cir2.x += cir2.vx;
cir2.y += cir2.vy;
if ( cir2.x – cir2.radius < 0 ) {
cir2.x = cir2.radius;
cir2.vx *= -1;
return;
}
if (cir2.x + cir2.radius > stage.stageWidth) {
cir2.x = stage.stageWidth – cir2.radius;
cir2.vx *= -1;
return;
}
if ( cir2.y  – cir2.radius< 0 ) {
cir2.y = cir2.radius;
cir2.vy *= -1;
return;
}
if ( cir2.y + cir2.radius> stage.stageHeight) {
cir2.y = stage.stageHeight – cir2.radius;
cir2.vy *= -1;
return;
}
}

本文来自: 拖拽 碰撞检测 代码片段