Question

I’m developing an app for iPhone 3.1.3.

I have the following class:

@interface Pattern : NSObject {

    NSMutableArray* shapes;
    NSMutableArray* locations;
    CGSize bounds;
}
@property (nonatomic, retain, readonly) NSMutableArray* shapes;
@property (nonatomic, retain, readonly) NSMutableArray* locations;

- (id) initWithNumShapes:(int)numShapes screenSize:(CGSize)screenSize;
- (void) addObject:(Object2D*) newObject;

@end

I don’t want to let programmers use -(id)init; because I need to setup my fields (shape, locations, bounds) on every initialization.

I don’t want to let programmers use this:

Pattern* myPattern = [[Pattern alloc] init];

I know how to implement:

- (id) initWithNumShapes:(int)numShapes screenSize:(CGSize) screenSize{
    if (self = [super init]) {
        shapes = [NSMutableArray arrayWithCapacity:numShapes];
        locations = [NSMutableArray arrayWithCapacity:numShapes];
        bounds = screenSize;
    }
    return (self);
}

How can I do that?

Answer 1

raise an exception if somebody uses the plain init

- (id)init {
    [NSException raise:@"MBMethodNotSupportedException" format:@"\"- (id)init\" is not supported. Please use the designated initializer \"- (id)initWithNumShapes:screenSize:\""];
    return nil;
}