// 1 UIButton -> clicked
[_baseButton addTarget:self action:@selector(toggleStack:) forControlEvents:UIControlEventTouchUpInside];
// 2 保证UIView 在屏幕中间
[stackView setCenter:CGPointMake(self.view.frame.size.width / 2 - 20 , self.view.frame.size.height / 2 )];
// 3 如何得到一个label的宽度
[label.text sizeWithAttributes:@{NSFontAttributeName : label.font}];
原文：http://www.cnblogs.com/puppyb2m/p/4539284.html