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KeyboardEvent事件as3代码

KeyboardEvent事件as3代码：

function drawBall(r:Number,color:uint):Sprite {
var sp:Sprite=new Sprite();
sp.graphics.beginGradientFill(GradientType.RADIAL,[0xffffff,color],[1,1],[0,r*3]);
sp.graphics.drawCircle(0,0,r);
sp.graphics.endFill();
return sp;
}
var sp:Sprite=drawBall(25,0xff1100);
addChild(sp);
sp.x=275;
sp.y=200;
stage.addEventListener(KeyboardEvent.KEY_DOWN,onKeyDown);
//stage.focus=sp;
//sp.addEventListener(KeyboardEvent.KEY_DOWN,onKeyDown);
/*如果用sp做事件的目标,则需指舞台焦点为sp,此时默认有矩形边框*/
function onKeyDown(e:KeyboardEvent):void {
switch (e.keyCode) {
case Keyboard.UP :
sp.y-=10;
break;
case Keyboard.DOWN :
sp.y+=10;
break;
case Keyboard.LEFT :
sp.x-=10;
break;
case Keyboard.RIGHT :
sp.x+=10;
break;
default :
break;
}
}