iOS动画实现：弹簧效果

源码地址：https://github.com/thermogl/TISpringLoadedViews,

这个比较复杂，我写了个简化版的：
https://www.dropbox.com/s/sv3yhm8dovh0adq/SpringDemo.zip http://download.csdn.net/detail/u010180166/5665977

- (void)simulateSpringWithDisplayLink:(CADisplayLink *)displayLink {

if (springEnabled && !self.panning){
CGPoint displacement = CGPointMake(self.center.x - restCenter.x,
self.center.y - restCenter.y);
//控件收到的力
CGPoint kx = CGPointMake(springConstant * displacement.x, springConstant * displacement.y);
//控件受到的阻力
CGPoint bv = CGPointMake(dampingCoefficient    * velocity.x, dampingCoefficient * velocity.y);
//加速度
CGPoint acceleration = CGPointMake((kx.x + bv.x) / mass, (kx.y + bv.y) / mass);

velocity.x -= (acceleration.x * displayLink.duration);
velocity.y -= (acceleration.y * displayLink.duration);

//设置控件新位置
CGPoint newCenter = self.center;
newCenter.x += (velocity.x * displayLink.duration);
newCenter.y += (velocity.y * displayLink.duration);
[self setCenter:newCenter];
}
}

这个方法由CADisplayLink负责调用，每秒钟默认60次。要看懂这段代码，首先你要了解弹簧的原理，比如拉起弹簧收到的力怎么计算，往回弹收到的阻力怎么计算。

 

下面是手势操作的代码，也就是拖动时触发的方法：

- (void)viewWasPanned:(UIPanGestureRecognizer *)sender {

CGPoint translation = CGPointApplyAffineTransform([sender translationInView:self.superview], CGAffineTransformMakeScale(panDragCoefficient, panDragCoefficient));
CGPoint translatedCenter = CGPointMake(self.center.x + translation.x, self.center.y + translation.y);

if (translation.x > 0 && (translatedCenter.x - restCenter.x) > panDistanceLimits.right){
translation.x -= (translatedCenter.x - restCenter.x) - panDistanceLimits.right;
}
else if (translation.x < 0 && (restCenter.x - translatedCenter.x) > panDistanceLimits.left){
translation.x += (restCenter.x - translatedCenter.x) - panDistanceLimits.left;
}

if (translation.y > 0 && (translatedCenter.y - restCenter.y) > panDistanceLimits.bottom){
translation.y -= (translatedCenter.y - restCenter.y) - panDistanceLimits.bottom;
}
else if (translation.y < 0 && (restCenter.y - translatedCenter.y) > panDistanceLimits.top){
translation.y += (restCenter.y - translatedCenter.y) - panDistanceLimits.top;
}

[self setCenter:CGPointMake(self.center.x + translation.x, self.center.y + translation.y)];
[sender setTranslation:CGPointZero inView:self.superview];
}