Objective-c – How to create Cocoa interfaces without Interface Builder

cocoaobjective c

I would prefer to create my interfaces programatically. Seems as if all the docs on Apple Developer assume you're using Interface Builder. Is it possible to create these interfaces programatically, and if so where do I start learning about how to do this

I thought the relevant document for this, if possible would be in this section: http://developer.apple.com/referencelibrary/Cocoa/idxUserExperience-date.html

Best Answer

I like the question, and I'd also like to know of resources for going IB-less. Usefulness (the "why") is limited only by imagination. Off the top of my head, here are some possible reasons to program UIs explicitly:

Implementing a better Interface Builder.
Programming dynamic UIs, i.e., ones whose structure is not knowable statically (at compile/xcode time).
Implementing the Cocoa back-end of a cross-platform library or language for UIs.

There is a series of blog posts on working without a nib and a recent description by Michael Mucha on cocoa-dev.

Related Solutions

Objective-c – How to print out a stack trace to the console/log in Cocoa

This code works on any thread:

NSLog(@"%@", NSThread.callStackSymbols);

Returns an array containing the call stack symbols. Each element is an NSString object with a value in a format determined by the backtrace_symbols() function.

Ios – How to create delegates in Objective-C

An Objective-C delegate is an object that has been assigned to the delegate property another object. To create one, you define a class that implements the delegate methods you're interested in, and mark that class as implementing the delegate protocol.

For example, suppose you have a UIWebView. If you'd like to implement its delegate's webViewDidStartLoad: method, you could create a class like this:

@interface MyClass<UIWebViewDelegate>
// ...
@end

@implementation MyClass
- (void)webViewDidStartLoad:(UIWebView *)webView { 
    // ... 
}
@end

Then you could create an instance of MyClass and assign it as the web view's delegate:

MyClass *instanceOfMyClass = [[MyClass alloc] init];
myWebView.delegate = instanceOfMyClass;

On the UIWebView side, it probably has code similar to this to see if the delegate responds to the webViewDidStartLoad: message using respondsToSelector: and send it if appropriate.

if([self.delegate respondsToSelector:@selector(webViewDidStartLoad:)]) {
    [self.delegate webViewDidStartLoad:self];
}

The delegate property itself is typically declared weak (in ARC) or assign (pre-ARC) to avoid retain loops, since the delegate of an object often holds a strong reference to that object. (For example, a view controller is often the delegate of a view it contains.)

Making Delegates for Your Classes

To define your own delegates, you'll have to declare their methods somewhere, as discussed in the Apple Docs on protocols. You usually declare a formal protocol. The declaration, paraphrased from UIWebView.h, would look like this:

@protocol UIWebViewDelegate <NSObject>
@optional
- (void)webViewDidStartLoad:(UIWebView *)webView;
// ... other methods here
@end

This is analogous to an interface or abstract base class, as it creates a special type for your delegate, UIWebViewDelegate in this case. Delegate implementors would have to adopt this protocol:

@interface MyClass <UIWebViewDelegate>
// ...
@end

And then implement the methods in the protocol. For methods declared in the protocol as @optional (like most delegate methods), you need to check with -respondsToSelector: before calling a particular method on it.

Naming

Delegate methods are typically named starting with the delegating class name, and take the delegating object as the first parameter. They also often use a will-, should-, or did- form. So, webViewDidStartLoad: (first parameter is the web view) rather than loadStarted (taking no parameters) for example.

Speed Optimizations

Instead of checking whether a delegate responds to a selector every time we want to message it, you can cache that information when delegates are set. One very clean way to do this is to use a bitfield, as follows:

@protocol SomethingDelegate <NSObject>
@optional
- (void)something:(id)something didFinishLoadingItem:(id)item;
- (void)something:(id)something didFailWithError:(NSError *)error;
@end

@interface Something : NSObject
@property (nonatomic, weak) id <SomethingDelegate> delegate;
@end

@implementation Something {
  struct {
    unsigned int didFinishLoadingItem:1;
    unsigned int didFailWithError:1;
  } delegateRespondsTo;
}
@synthesize delegate;

- (void)setDelegate:(id <SomethingDelegate>)aDelegate {
  if (delegate != aDelegate) {
    delegate = aDelegate;

    delegateRespondsTo.didFinishLoadingItem = [delegate respondsToSelector:@selector(something:didFinishLoadingItem:)];
    delegateRespondsTo.didFailWithError = [delegate respondsToSelector:@selector(something:didFailWithError:)];
  }
}
@end

Then, in the body, we can check that our delegate handles messages by accessing our delegateRespondsTo struct, rather than by sending -respondsToSelector: over and over again.

Informal Delegates

Before protocols existed, it was common to use a category on NSObject to declare the methods a delegate could implement. For example, CALayer still does this:

@interface NSObject(CALayerDelegate)
- (void)displayLayer:(CALayer *)layer;
// ... other methods here
@end

This tells the compiler that any object might implement displayLayer:.

You would then use the same -respondsToSelector: approach as described above to call this method. Delegates implement this method and assign the delegate property, and that's it (there's no declaring you conform to a protocol). This method is common in Apple's libraries, but new code should use the more modern protocol approach above, since this approach pollutes NSObject (which makes autocomplete less useful) and makes it hard for the compiler to warn you about typos and similar errors.