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identity inspector 的key path 可以用来做圆角按钮和边框。
layer.cornerRadius number 圆角按钮
[self performSelectorOnMainThread:@selector(updateUI:) withObject:image waitUntilDone:YES];
layout有三种方式：Manual layout，Autoresizing，Autolayout。我们常用的可能就后面两种。
假设v1是一个不使用autolayout的view，而v2是一个使用autolayout的view，但v1成为v2的subview时，
v2需要四条隐含的constraint来确定v1的位置，这些约束都是从v1的frame转化而来：
This conversion is performed only if the view in question has its translates-
AutoresizingMaskIntoConstraints property set to YES. That is, in fact, the default if
the view came into existence either in code or by instantiation from a nib where “Use
Auto Layout” is not checked. The assumption is that if a view came into existence in
either of those ways, you want its frame and autoresizingMask to act as its constraints
self.navigationController popToRootViewControllerAnimated:YES]UIViewController *prevVC = [self.navigationController.viewControllers objectAtIndex:<n>];
[self.navigationController popToViewController:prevVC animated:YES];
[self.navigationController popViewControllerAnimated:YES];
willMoveToParentViewController: method of the child view controller before calling the removeFromParentViewController method...Thus, as discussed in Adding and Removing a Child section of the View Controller Programming Guide, when removing a child, we should:
[childVC willMoveToParentViewController:nil];
[childVC.view removeFromSuperview];
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原文地址：http://www.cnblogs.com/loying/p/4811356.html
