Swift开发：AutoResizing实现自动布局

         /*
        autoresizing需求：
        添加一个红色view ，放在主控制器的右下角，且距离右下角边框为20
        不管横屏还是竖屏还是屏幕大小改变，红色view的位置不能改变，使用
        代码添加autoresizing
        */
        let redView = UIView()
        
        let wh:CGFloat = 100
        let x:CGFloat = self.view.frame.size.width - wh - 20.0
        let y:CGFloat = self.view.frame.size.height - wh - 20.0
        redView.frame = CGRectMake(x,y,wh,wh)
        redView.backgroundColor = UIColor.redColor()
        
        
        var arm1 = UIViewAutoresizing.None
        
        arm1.unionInPlace(UIViewAutoresizing.FlexibleRightMargin)
        arm1.unionInPlace(UIViewAutoresizing.FlexibleLeftMargin)
        arm1.unionInPlace(UIViewAutoresizing.FlexibleBottomMargin)
        arm1.unionInPlace(UIViewAutoresizing.FlexibleTopMargin)
        
        redView.autoresizingMask = arm1
        
        print(redView.autoresizingMask)
        
        self.view.addSubview(redView)

oc写法

    UIView * redView = [[ UIView alloc]init];
    redView.backgroundColor = [UIColor redColor];
    CGFloat wh = 100;
    CGFloat x = self.view.frame.size.width - wh;
    CGFloat y = self.view.frame.size.height - wh;
    
    redView.frame = CGRectMake(x, y, wh, wh);
    
    redView.autoresizingMask = UIViewAutoresizingFlexibleBottomMargin | UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleTopMargin | UIViewAutoresizingFlexibleLeftMargin;
    
    [self.view addSubview:redView];