I’m create a cocoa touch framework to share some common code between my apps.
I need to pass an instance of a class into a method, which has some specific properties.
The method will be called from the app.
I’m quite new to using protocols.
Should I create a protocol h file in my framework with all the properties required by the function.
If so can I pass the protocol as the type of the instance variable into the function?
If not how can achieve this?
Yes, you can. Here's an example.
First, declare your protocol in a .h file:
@protocol Vehicle <NSObject>
@property NSNumber * numberOfWheels;
@required
-(void)engineOn;
@end
Declare the classes which conform to your protocol:
#import "Vehicle.h"
@interface Car : NSObject <Vehicle>
@end
Implement the required methods and synthesise the properties:
@implementation Car
@synthesize numberOfWheels;
-(void)engineOn {
NSLog(@"Car engine on");
}
@end
and another, for the sake of example:
#import "Vehicle.h"
@interface Motorcycle : NSObject <Vehicle>
@end
@implementation Motorcycle
@synthesize numberOfWheels;
-(void)engineOn {
NSLog(@"Motorcycle engine on");
}
@end
When you declare a method which you want to accept a Vehicle argument, you use the generic id type and specify that any object passed in should conform to Vehicle:
#import "Vehicle.h"
@interface Race : NSObject
-(void)addVehicleToRace:(id<Vehicle>)vehicle;
@end
Then, in the implementation for that method, you can use the properties and methods declared in the protocol, regardless of the concrete type that has been passed in:
@implementation Race
-(void)addVehicleToRace:(id<Vehicle>)vehicle {
[vehicle engineOn];
}
@end
Then, as you'd expect, you can pass in instances of concrete classes that conform to your protocol:
Motorcycle *cycle = [[Motorcycle alloc] init];
cycle.numberOfWheels = 2;
Car *car = [[Car alloc] init];
car.numberOfWheels = 4;
Race *race = [[Race alloc] init];
[race addVehicleToRace:car];
[race addVehicleToRace:cycle];
And the appropriate concrete implementation of the protocol's methods will be executed, depending on the actual concrete types that you pass as a parameter:
2018-10-15 13:53:45.039596+0800 ProtocolExample[78912:1847146] Car engine on
2018-10-15 13:53:45.039783+0800 ProtocolExample[78912:1847146] Motorcycle engine on