IPhone、IPad经常会遇到横竖屏切换，或者需要自动调整大小。如果你的界面不能用storyboard和xib来生成界面的话，先把控制器视图的frame属性值固定下来，然后添加subview（子视图）的时候，就可以使用视图继承类（UIView） 自带的 autoresizingMask 属性，之后如果横竖屏切换，或者是使用UIPopoverController之类的方法，就可以只设置一次frame属性，以后的frame属性都是自适应的（frame缩小太多的话效果不好，根据情况而定）。
{
UIViewAutoresizingNone = 0,
UIViewAutoresizingFlexibleLeftMargin = 1 << 0,
UIViewAutoresizingFlexibleWidth = 1 << 1,
UIViewAutoresizingFlexibleRightMargin = 1 << 2,
UIViewAutoresizingFlexibleTopMargin = 1 << 3,
UIViewAutoresizingFlexibleHeight = 1 << 4,
UIViewAutoresizingFlexibleBottomMargin = 1 << 5
};
typedef NSUInteger UIViewAutoresizing;
UIViewAutoresizingFlexibleLeftMargin 视图靠右对齐
UIViewAutoresizingFlexibleWidth 视图自适应宽度
UIViewAutoresizingFlexibleRightMargin 视图靠左对齐
UIViewAutoresizingFlexibleTopMargin 视图靠下对齐
UIViewAutoresizingFlexibleHeight 视图自适应高度
UIViewAutoresizingFlexibleBottomMargin 视图靠上对齐
注意：LeftMargin、RightMargin、TopMargin、BottomMargin的实际对齐方向是相反的
示例：让按钮始终在 ViewController 的右上角显示：
- (
void
)viewDidLoad
{
[super viewDidLoad];
UIButton
*right =
[UIButton buttonWithType:UIButtonTypeRoundedRect];
right.frame
= CGRectMake(self.view.frame.size.width-
300
,
0
,
300
,
300
);
right.autoresizingMask
= UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleBottomMargin | UIViewAutoresizingFlexibleWidth |
UIViewAutoresizingFlexibleHeight;
[right setTitle:
@"
456
"
forState:UIControlStateNormal];
[self.view addSubview:right];
}
