One line lazy property definition, with auto triggering, custom selectors

ARC only, XCode 4.4 minimum (For auto synthesized properties)

Description

Dealing with lazy properties can be cumbersome sometimes, copy/pasting same code again and again.
This code can be disturbing when reading source file.
Sometimes, you have to execute some code on property initialisation.

More information on lazy instanciation on Wikipedia

Usage

• Declare a strong nonatomic property for an object type
  • @property (nonatomic, strong)
• Add one of these macros at the end of your file with property name, before end of class implementation @end
  • LAZY_PROPERTY(propertyName)
  • LAZY_PROPERTY_CUSTOM_SELECTOR(propertyName, @selector(customSelectorName:), @[@"parameter"])
• Optionally declare autotriggered methods. Auto triggered methods are named after property name, camelcase style, prefixed by configure
  • - (void)configurePropertyName ...
• Triggered method can take an optional parameter, that is the object parameter of LAZY_PROPERTY_CUSTOM_SELECTOR macro.
  • - (void)configurePropertyName:(MyParameter *)aParameter ...

Example

RootViewController.m

@interface DemoViewController ()
...

// Lazy properties
@property (nonatomic, strong) SimpleViewController *simpleViewController; // Will be used modally
@property (nonatomic, strong) DetailViewController *detailViewController; // Will be pushed from tableview
@end

@implementation DemoViewController
...

#pragma mark - UITableViewDelegate methods
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    // No need to worry about detail view controller instantiation. It will be created at first call
    // This allows you to keep your code super clear
    [self.navigationController pushViewController:self.detailViewController
                                         animated:YES];
}

#pragma mark - UIActions
- (IBAction)showModal:(id)sender
{
    // No need to worry about view controller instantiation here too. It will be created at first call
    // First configuration was moved to a dedicated method, auto triggered on object creation
    [self presentViewController:self.simpleViewController
                       animated:YES
                     completion:nil];
}

#pragma mark - Configuration methods
// This method will be autotriggered when simpleViewController will be instantiated
- (void)configureSimpleViewController
{
    // This methods will be called only once, so you can perform initial configuration here
    _simpleViewController.backgroundColor = [UIColor redcolor];
}

// Magic happens here. Write macros at the end of the file, to keep it clean. Use property name
LAZY_PROPERTY(simpleViewController);
LAZY_PROPERTY(detailViewController);
@end

You will find more examples in provided sample, such as using custom selector.

Use case

• View controller to be presented modally
• View controller to be pushed after selecting a row in a table view, to display a detail
• UserInfo NSMutableDictionary associated to a class
• MoviePlayer used in a detail view controller, needing customisation when initialised
• To infinity and beyond

Let me know if you have some other use cases

Advantages

• Type less, do more
• Reduce amount of typed code
• Be focused on logic / business code instead of memory management
• Split configuration code from workflow
• Perform fastidious initialisation in less lines of code
• Reduce memory footprint, by not allocating unused objects

Consideration

• Be careful, especially with UI Object, because initialisation will be on calling thread
• Generated ivar will remain nil until property is accessed once
• You can directly access to generated ivar (_propertyName), without triggering initialisation
• init constructor is used by default
• Don't add @synthesize on your code
• Don't declare ivar

Limitations

Only strong properties are supported. Lazy weak properties may instantiate a new instance at each call. atomic properties are not supported. When overriding atomic properties, you have to override getter and setter. Using LazyProperty on an atomic property will result in compiler a warning message.

Installation

Cocoapods: pod 'LazyProperty'
Manual: Copy the Classes folder in your project

Import header in your project. .pch is a good place ;)

#import "LazyProperty.h"

Versions

1.0 : Initial release 1.1 : Added some tests, triggered method can have a parameter, removed @synchronized from generated getter

Team

Nicolas Goutaland