Plug-in Architectures in Cocoa Katsuma Tanaka 

@questbeat 

Plug-in Architectures in Cocoa - Sample program is available on GitHub. https://github.com/questbeat/PlugInSample 

Introduction: Creating Xcode Plug-in 

- github.com/questbeat/Lin Creating Xcode Plug-in 

Creating Xcode Plug-in - Create a new project. 

+ (void)pluginDidLoad:(NSBundle *)plugin { [self sharedPlugin]; } + (id)sharedPlugin { static id sharedPlugin = nil; static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ sharedPlugin = [[self alloc] init]; }); } Creating Xcode Plug-in - Lin.m 

- Info.plist Creating Xcode Plug-in - Build settings 

- Install the plug-in in the appropriate folder. Creating Xcode Plug-in 

- Installation can be easier by Installation Directory settings. Creating Xcode Plug-in 

- Plug-in works on the same process as Xcode. Creating Xcode Plug-in 

What is a plug-in? - A plug-in is a loadable bundle that adds functionality to an application. MyBundle.bundle/ Contents/ Info.plist Frameworks/ MacOS/ Resources/ ... 

- Application (.app) - Framework (.framework) - Preference Pane (.prefPane) - Screen Saver (.saver) - Xcode Plug-in (.xcplugin) Loadable Bundles are used in ... 

Loading Bundles 

1. Locate the bundle 2. Load the bundle’s executable code 3. Instantiate an object of the principal class Loading Bundles Basic Three Steps 

MyApp.app/ Contents/ PlugIns/ MyPlugin.bundle Resources/ Frameworks/ ... Locating Bundles Standard Location 

NSBundle *appBundle = [NSBundle mainBundle]; NSString *plugInsPath = [appBundle builtInPlugInsPath]; “/Applications/MyApp.app/Contents/PlugIns” Standard Location Locating Bundles 

MyApp.app/ Contents/ Resources/ PlugIns/ MyPlugin.bundle Frameworks/ ... Nonstandard Location Locating Bundles 

NSBundle *appBundle = [NSBundle mainBundle]; NSArray *bundlePaths = [appBundle pathsForResourcesOfType:@"bundle" inDirectory:@"PlugIns"]; Nonstandard Location Locating Bundles 

/Users/questbeat/Library/Application Support/MyApp/PlugIns User-speci c /Library/Application Support/MyApp/PlugIns /Network/Library/Application Support/MyApp/PlugIns System-wide Network Support Library Directories Locating Bundles 

NSString *appSupportSubpath = @"Application Support/MyApp/PlugIns"; NSMutableArray *bundleSearchPaths = [NSMutableArray array]; NSArray *librarySearchPaths = NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSAllDomainsMask - NSSystemDomainMask, YES); for (NSString *path in librarySearchPaths) { [bundleSearchPaths addObject:[path stringByAppendingPathComponent:appSupportSubpath]]; } Support Library Directories Locating Bundles 

1. Locate the bundle 2. Load the bundle’s executable code 3. Instantiate an object of the principal class Loading Bundles Basic Three Steps 

NSString *bundlePath = ...; NSBundle *bundle = [NSBundle bundleWithPath:bundlePath]; Creating a NSBundle Object 

NSString *bundlePath = ...; NSBundle *bundle = [NSBundle bundleWithPath:bundlePath]; if ([bundle load]) { NSLog(@"Bundle was successfully loaded."); } Loading Code 

Loading Code and Get Errors NSString *bundlePath = ...; NSBundle *bundle = [NSBundle bundleWithPath:bundlePath]; NSError *error = nil; if (![bundle loadAndReturnError:&error]) { NSLog(@"Error: %@", [error localizedDescription]); } 

Checking Code without Loading NSString *bundlePath = ...; NSBundle *bundle = [NSBundle bundleWithPath:bundlePath]; NSError *error = nil; if (![bundle preflightAndReturnError:&error]) { NSLog(@"Error: %@", [error localizedDescription]); } 

Unloading Code NSString *bundlePath = ...; NSBundle *bundle = [NSBundle bundleWithPath:bundlePath]; [bundle load]; if ([bundle isLoaded] && [bundle unload]) { NSLog(@"Bundle was successfully unloaded."); } 

1. Locate the bundle 2. Load the bundle’s executable code 3. Instantiate an object of the principal class Loading Bundles Basic Three Steps 

Retrieving the Principal Class 

NSString *bundlePath = ...; NSBundle *bundle = [NSBundle bundleWithPath:bundlePath]; Class principalClass = [bundle principalClass]; Retrieving the Principal Class 

NSString *bundlePath = ...; NSBundle *bundle = [NSBundle bundleWithPath:bundlePath]; Class someClass = [bundle classNamed:@"MyAppController"]; Retrieving the Principal Class 

NSString *bundlePath = ...; NSBundle *bundle = [NSBundle bundleWithPath:bundlePath]; Class principalClass = [bundle principalClass]; id instance = [[principalClass alloc] init]; Instantiating the Principal Class 

Instantiating the Principal Class NSString *bundlePath = ...; NSBundle *bundle = [NSBundle bundleWithPath:bundlePath]; Class principalClass = [bundle principalClass]; id instance = [[principalClass alloc] init]; [instance greet]; @protocol MyPlugIn - (void)greet; @end ... - Host application should provide an interface. 

Creating Plug-in Architectures 

- Use a formal protocol - Use an informal protocol - Use an abstract base class Creating Plug-in Architectures Three Ways to Provide Interface 

#import @protocol MyAppBitmapGraphicsFiltering @required // Returns the version of the interface you're implementing. - (unsigned)interfaceVersion; // Filters the bitmap and returns a modified version. - (NSBitmapImageRep *)filteredImageRep:(NSBitmapImageRep *)imageRep; @optional // Returns what to display in the Filter menu. - (NSString *)menuItemString; // Returns the window controller for the settings configuration window. - (NSWindowController *)configurationWindowController; @end Use a Formal Protocol 

#import @interface NSObject (MyAppBitmapGraphicsFiltering) // REQUIRED // Returns the version of the interface you're implementing. - (unsigned)interfaceVersion; // REQUIRED // Filters the bitmap and returns a modified version. - (NSBitmapImageRep *)filteredImageRep:(NSBitmapImageRep *)imageRep; // OPTIONAL // Returns what to display in the Filter menu. - (NSString *)menuItemString; // OPTIONAL // Returns the window controller for the settings configuration window. - (NSWindowController *)configurationWindowController; @end Use an Informal Protocol 

#import @interface MyAppEmbeddingView : NSView { @private NSURL *_URL; void *_reserved1; void *_reserved2; void *_reserved3; } - (id)initWithFrame:(NSRect)frameRect URL:(NSURL)URL; - (unsigned)interfaceVersion; - (NSURL *)URL; - (void)setURL:(NSURL *)URL; @end Use an Abstract Base Class 

#import "MyAppEmbeddingView.h" @implementation MyAppEmbeddingView - (id)initWithFrame:(NSRect)frameRect URL:(NSURL)URL { self = [self initWithFrame:frameRect]; if (self) { self.URL = URL; } return self; } - (unsigned)interfaceVersion { return 0; } ... Use an Abstract Base Class 

- (void)drawRect:(NSRect)rect { NSEraseRect(rect); } - (NSURL *)URL { return _URL; } - (void)setURL:(NSURL *)URL { _URL = URL; } @end ... Use an Abstract Base Class 

- (BOOL)plugInClassIsValid:(Class)plugInClass { if ([plugInClass conformsToProtocol:@protocol(MyAppBitmapGraphicsFiltering)]) { if ([plugInClass instancesRespondToSelector:@selector(interfaceVersion)] && [plugInClass instancesRespondToSelector:@selector(filteredImageRep)]) { return YES; } } return NO; } Formal Protocol Validating Plug-ins 

- (BOOL)plugInClassIsValid:(Class)plugInClass { if ([plugInClass instancesRespondToSelector:@selector(interfaceVersion)] && [plugInClass instancesRespondToSelector:@selector(filteredImageRep)]) { return YES; } return NO; } Validating Plug-ins Informal Protocol 

- (BOOL)plugInClassIsValid:(Class)plugInClass { if ([plugInClass isSubclassOfClass:[MyAppEmbeddingView class]]) { return YES; } return NO; } Abstract Base Class Validating Plug-ins 

Sample Program 

Summary - Plug-in is a loadable bundle. - Bundle is easily accessible through NSBundle. - There are three choices for plug-in architecture in Cocoa: - Formal protocol - Informal protocol - Abstract base class 

References - Code Loading Programming Topics https://developer.apple.com/library/mac/ #documentation/Cocoa/Conceptual/LoadingCode/ LoadingCode.html https://developer.apple.com/library/mac/ #documentation/Cocoa/Reference/Foundation/Classes/ NSBundle_Class/Reference/Reference.html - NSBundle Class Reference 

Thank you