autoresizingMask属性

autoresize只能设置父子控件之间的位置关系！

    UIView *redView = [[UIView alloc] init];
    
    redView.frame = CGRectMake(self.view.frame.size.width-250, self.view.frame.size.height-250, 200, 200);
    redView.backgroundColor = [UIColor redColor];
    [self.view addSubview:redView];
    /**
     UIViewAutoresizingNone
     UIViewAutoresizingFlexibleLeftMargin   距离父控件左边可以拉伸
     UIViewAutoresizingFlexibleWidth        宽度会随父控件的宽度进行拉伸
     UIViewAutoresizingFlexibleRightMargin  距离父控件右边可以拉伸
     UIViewAutoresizingFlexibleTopMargin    距离父控件顶部可以拉伸
     UIViewAutoresizingFlexibleHeight       宽度会随父控件的高度进行拉伸
     UIViewAutoresizingFlexibleBottomMargin 距离父控件底部可以拉伸
     */
    // 在屏幕右下角，保持右边50，底部50，高度和宽度碎屏幕拉伸
    redView.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin| UIViewAutoresizingFlexibleTopMargin|UIViewAutoresizingFlexibleWidth|UIViewAutoresizingFlexibleHeight;