Michael Dorner Michael Dorner - 11 months ago 76
Objective-C Question

Abstract class in Objective-C

I need your help. Following problem in Objective-C:

// Robot.h
@protocol RobotProtocol <NSObject>
-(void)doWork;
@end

@interface Robot : NSObject


// Rob1 sublass of class Robot
// rob1.h
@interface Rob1 : Robot <RobotProtocol>

// rob1.m
@implementation
-(void)doWork
{
// print 'robot 1'
}


// Rob2 sublass of class Robot
// rob2.h
@interface Rob2 : Robot <RobotProtocol>

// rob2.m
@implementation
-(void)doWork
{
// print 'robot 2'
}



// Task.h
@interface Task : NSObject
{
Robot *rob;
}


// Task.m
@implementation
- (id)init
{
if ([super init]) {
rob = [[Rob1 alloc] init]; // or Rob2 !!
}
return self;
}

-(void)doSomething
{
[rob doWork]; // how to make sure, that this is implemented, depending on Rob1 or Rob2
}


How should
Robot
and its subclasses be implemented, that
Robot *rob
can be one of the subclasses of Robot
rob1
,
rob2
,
...
and the method
doWork:(BOOL)val;
can be called? My first idea was to implement
Robot
as an abstract class, but unfortunately there are no abstract classes in Objective-C...

At the moment I am using a protocol, but I am not confident. Because it is not sure, that doWork is implemented, the compiler complains about


'Robot' may not respond to 'doWork'


Thank you for your ideas.

Answer Source

Protocols should work.

@protocol RobotProtocol <NSObject>
@required
- (void)doWork:(BOOL)flag;
@end

@interface Robot1 : NSObject <RobotProtocol>
@end

@implementation Robot1
- (void)doWork:(BOOL)flag
{
}
@end

Unit Test for Robot1 called though id<RobotProtocol>

- (void)testRobot
{
    id<RobotProtocol> robot = [[Robot1 alloc] init];
    [robot doWork:YES];
}

Update

After looking at your code, @interface Robot : NSObject should be @interface Robot : NSObject <RobotProtocol>. The thing is you don't need @interface Robot : NSObject <RobotProtocol> at all. You can just use id<RobotProtocol>. This is the name of your abstract class.