在iOS中是否有一个始终被调用的init方法？

Question

Is there a method that is always called in Cocoa? Many classes have init or initWith , but even worse they can be loaded from a nib or something. I don't want to have to scrape around and find how it does this in this case. I just want to set some initial variables and other things, and I want a method to subclass that I can depend on no matter if it's a UIView , UIViewController or UITableViewCell etc.

Answer 1

No there is not such a method. init comes from NSObject so every object can use it, and as well subclasses define their own initialization methods. UIView , for example, defines initWithFrame: and furthermore there are init methods from protocols, such as NSCoding which defines initWithCoder: . This is the dynamic nature of objective-C, anything can be extended at any time. That being said, there are some patterns. UIViewController almost always takes initWithNibName:bundle: and UIView almost always takes initWithFrame: or initWithCoder: . What I do is make an internal initialize method, and just have the other inits call it.

- (void)initialize
{
    //Do stuff
}

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if(self)
    {
        [self initialize];
    }
}

- (id)initWithCoder:(NSCoder *)aCoder
{
    self = [super initWithCoder:aCoder];
    if(self)
    {
        [self initialize];
    }
}

Answer 2

Not 100% sure that it is always called, but I am pretty sure that this is a viable option. To be perfectly honest, I can't recall that I have ever seen this method used in practice and I usually shy away from using this method (I have absolutely no idea why, probably because it's just not the cleanest and most comprehensive method to achieve this...):

-didMoveToSuperview()

From documentation:

Tells the view that its superview changed. The default implementation of this method does nothing. Subclasses can override it to perform additional actions whenever the superview changes.

Answer 3

There's many ways you can write a custom initializer.

- (id)initWithString:(NSString *)string {
    if((self == [super init])) {
        self.string = string;
    }
    return self;
}

That's just how I write my initializers in general. For example, the one above takes a string. (you don't have to pass strings if you don't want).

Btw, init is a method. According to the header for NSObject, init has a method implementation.