Autoresizing

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    UIView *redView = [[UIView alloc] init];
    redView.backgroundColor = [UIColor redColor];
    CGFloat redViewX = self.view.frame.size.width - 100;
    CGFloat redViewY = self.view.frame.size.height - 100;
    redView.frame = CGRectMake(redViewX, redViewY, 100, 100);

    /**
     UIViewAutoresizingFlexibleLeftMargin 距离父控件的左边是可以伸缩的
     UIViewAutoresizingFlexibleBottomMargin 距离父控件的底部是可以伸缩的
     UIViewAutoresizingFlexibleRightMargin 距离父控件的右边是可以伸缩的
     UIViewAutoresizingFlexibleTopMargin 距离父控件的顶部是可以伸缩的
     UIViewAutoresizingFlexibleHeight 高度跟随父控件的高度进行伸缩
     UIViewAutoresizingFlexibleWidth 宽度跟随父控件的宽度进行伸缩

     */
    redView.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleTopMargin | UIViewAutoresizingFlexibleWidth;
    [self.view addSubview:redView];
}

@end