Question

I have the following simple class definition:

//mycommon.h

@interface CurrentPath : NSObject
@property (nonatomic, strong) NSString* PathString;
@property (nonatomic, strong) NSMutableArray* PathArr;
- (void) addAddressToPath:(NSString*) address;
@end

//mycommon.m

@implementation CurrentPath : NSObject

@synthesize PathString;
@synthesize PathArr;

- (void) addAddressToPath:(NSString*) address{
    NSLog(@"addAddressToPath...");

    // Add to string
    self.PathString = [self.PathString stringByAppendingString:address];

    // Add to Arr
    [self.PathArr addObject:address];
}

@end

In another class I do #import<mycommon.h> and declare the variable like this:

@interface myDetailViewController : 
{
        CurrentPath* currentPath;
}
- (void) mymethod;
    @end

and in

@implementation myDetailViewController

- void mymethod{
self->currentPath = [[CurrentPath alloc] init];
NSString* stateSelected = @"simple";
    [self->currentPath addAddressToPath:stateSelected];
}
@end

Problem is that the PathString and PathArr properties of self->currentPath are empty after this method call which I think should have “simple” in them. Please help!

Answer 1

You have to make sure that your NSString and NSMutableArray properties are initialized when your CurrentPath object is created. Otherwise, the call to stringByAppendingString will result in nil because it is sent to a nil object.

One feasible way would perhaps be

self.currentPath = [NSString string];
// or
self.currentPath = @"";
[self.currentPath addAddressToPath:@"simple"];

More elegant and robust would be to check for nil property in the addAddressToPath method.

if (!self.pathString) self.pathString = [NSString string]; 
if (!self.pathArr) self.pathArr = [NSMutableArray array];

Notice that am following the objective-c convention and use property names that start with lower case letters.