自动布局视图控制器继承

Question

I have a ViewController called LoginViewController, and it holds a couple of textfields and a button.

All elements are working great with auto layout (rules built programmatically), in this case the elements are centered at X with its superview.

Now, I want to create a UIViewController which hesitance from LoginViewController, called LeftLoginViewController. This LeftLoginViewController has the same functionality of LoginViewController, but the appearance changes, it should sustain all the elements to the left of the superview.

(This leftLoginViewController is an example, my question is focusing how should I manage a situation where I want to move visual elements in the father's view)

What's the best way to accomplish this? To modify the autolayout rules? Because obviously you cannot modify the frame.

Should I create properties for each rule added in the main View of the parentViewController? and the LeftLoginViewController can modify their constant? What happen if I want to change one of the rules like for example NSLayoutAttributeCenterX to NSLayoutAttributeTrailing, that property is read only.

Sorry, but I'm very confused about this, I need some ideas to get the right direcction.

Answer 1

If the only difference in LeftLoginViewController is its layout, you don't need a child class. You can init your view controller with a type.

Assuming you're using Objective-C:

ViewController.h

typedef NS_ENUM(NSUInteger, LayoutType) {
    LayoutTypeNormal,
    LayoutTypeLeft
};

@interface ViewController : UIViewController

- (id)initWithLayoutType:(LayoutType)layoutType;

@end

ViewController.m

@interface ViewController()

@property (nonatomic) LayoutType layoutType;

@end

@implementation ViewController

- (id)initWithLayoutType:(LayoutType)layoutType
{
    self = [super init];
    if (self)
    {
        self.layoutType = layoutType;
    }

    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    if (self.layoutType == LayoutTypeNormal)
    {
        // centre layout for normal
    }
    else if (self.layoutType == LayoutTypeLeft)
    {
        // left layout
    }
}