// popAnimation transition
if (!animation) {
animation = [POPSpringAnimation animation];
animation.springBounciness = 5;
animation.springSpeed = 10;
animation.property = [POPAnimatableProperty propertyWithName:@"popAnimationProgress" initializer:^(POPMutableAnimatableProperty *prop) {
prop.readBlock = ^(ViewController *obj, CGFloat values[]) {
values[0] = obj.popAnimationProgress;
};
prop.writeBlock = ^(ViewController *obj, const CGFloat values[]) {
obj.popAnimationProgress = values[0];
};
prop.threshold = 0.001;
}];
[self pop_addAnimation:animation