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-rw-r--r--objective-c.html.markdown70
1 files changed, 67 insertions, 3 deletions
diff --git a/objective-c.html.markdown b/objective-c.html.markdown
index 47af5ae8..9e41e135 100644
--- a/objective-c.html.markdown
+++ b/objective-c.html.markdown
@@ -449,7 +449,9 @@ distance = 18; // References "long distance" from MyClass implementation
@end // States the end of the implementation
+///////////////////////////////////////
// Categories
+///////////////////////////////////////
// A category is a group of methods designed to extend a class. They allow you to add new methods
// to an existing class for organizational purposes. This is not to be mistaken with subclasses.
// Subclasses are meant to CHANGE functionality of an object while categories instead ADD
@@ -553,7 +555,9 @@ int main (int argc, const char * argv[]) {
@end
+///////////////////////////////////////
// Extensions
+///////////////////////////////////////
// Extensions allow you to override public access property attributes and methods of an @interface.
// @interface filename: Shape.h
@interface Shape : NSObject // Base Shape class extension overrides below.
@@ -588,15 +592,75 @@ int main (int argc, const char * argv[]) {
@end
-
+///////////////////////////////////////
// Protocols
+///////////////////////////////////////
// A protocol declares methods that can be implemented by any class.
// Protocols are not classes themselves. They simply define an interface
// that other objects are responsible for implementing.
-@protocol MyProtocol
- - (void)myProtocolMethod;
+ // @protocol filename: "CarUtilities.h"
+@protocol CarUtilities <NSObject> // <NSObject> => Name of another protocol this protocol includes.
+ @property BOOL engineOn; // Adopting class must @synthesize all defined @properties and
+ - (void)turnOnEngine; // all defined methods.
+@end
+// Below is an example class implementing the protocol.
+#import "CarUtilities.h" // Import the @protocol file.
+
+@interface Car : NSObject <CarUtilities> // Name of protocol goes inside <>
+ // You don't need the @property or method names here for CarUtilities. Only @implementation does.
+- (void)turnOnEngineWithUtilities:(id <CarUtilities>)car; // You can use protocols as data too.
+@end
+// The @implementation needs to implement the @properties and methods for the protocol.
+@implementation Car : NSObject <CarUtilities>
+
+@synthesize engineOn = _engineOn; // Create a @synthesize statement for the engineOn @property.
+
+- (void)turnOnEngine { // Implement turnOnEngine however you would like. Protocols do not define
+ _engineOn = YES; // how you implement a method, it just requires that you do implement it.
+}
+// You may use a protocol as data as you know what methods and variables it has implemented.
+- (void)turnOnEngineWithCarUtilities:(id <CarUtilities>)objectOfSomeKind {
+ [objectOfSomeKind engineOn]; // You have access to object variables
+ [objectOfSomeKind turnOnEngine]; // and the methods inside.
+ [objectOfSomeKind engineOn]; // May or may not be YES. Class implements it however it wants.
+}
+
@end
+// Instances of Car now have access to the protocol.
+Car *carInstance = [[Car alloc] init];
+[[carInstance setEngineOn:NO];
+[carInstance turnOnEngine];
+if ([carInstance engineOn]) {
+ NSLog(@"Car engine is on."); // prints => "Car engine is on."
+}
+// Make sure to check if an object of type 'id' implements a protocol before calling protocol methods:
+if ([myClass conformsToProtocol:@protocol(CarUtilities)]) {
+ NSLog(@"This does not run as the MyClass class does not implement the CarUtilities protocol.");
+} else if ([carInstance conformsToProtocol:@protocol(CarUtilities)]) {
+ NSLog(@"This does run as the Car class implements the CarUtilities protocol.");
+}
+// Categories may implement protocols as well: @interface Car (CarCategory) <CarUtilities>
+// You may implement many protocols: @interface Car : NSObject <CarUtilities, CarCleaning>
+// NOTE: If two or more protocols rely on each other, make sure to forward-declare them:
+#import "Brother.h"
+
+@protocol Brother; // Forward-declare statement. Without it, compiler would through error.
+
+@protocol Sister <NSObject>
+
+- (void)beNiceToBrother:(id <Brother>)brother;
+@end
+// See the problem is that Sister relies on Brother, and Brother relies on Sister.
+#import "Sister.h"
+
+@protocol Sister; // These lines stop the recursion, resolving the issue.
+
+@protocol Brother <NSObject>
+
+- (void)beNiceToSister:(id <Sister>)sister;
+
+@end
///////////////////////////////////////
// Memory Management