//1.设置阴影颜色

self.navigationController.navigationBar.layer.shadowColor = [UIColor blackColor].CGColor;

//2.设置阴影偏移范围

self.navigationController.navigationBar.layer.shadowOffset = CGSizeMake(0, 10);

//3.设置阴影颜色的透明度

self.navigationController.navigationBar.layer.shadowOpacity = 0.2;

//4.设置阴影半径

self.navigationController.navigationBar.layer.shadowRadius = 16;

//5.设置阴影路径

self.navigationController.navigationBar.layer.shadowPath = [UIBezierPath bezierPathWithRect:self.navigationController.navigationBar.bounds].CGPath;

通过设置1.2.3步导航阴影就可以出现,如果对阴影有特别的需要,可再设置4.5这两个步骤.