Accessing an array of dictionaries in Objective-C

Question

So, having a hard time dereferencing some data I've loaded into arrays and dictionaries:

Inside a controller:

- (void)setupVendorsArray {
    self.vendorsArray = [NSArray arrayWithObjects:@"Toyota", @"Honda",nil];
}

- (void)setupProductFamiliesHash {

    NSArray *lowcost = [NSArray arrayWithObjects:@"Corolla", @"Fit",nil];
    NSArray *midrange = [NSArray arrayWithObjects:@"Camry", @"Accord",nil];
    NSArray *highend = [NSArray arrayWithObjects:@"Lexus", @"Acura",nil];
    NSArray *trucks = [NSArray arrayWithObjects:@"Tacoma", @"Ridgeline",nil];

    NSDictionary *lc = [NSDictionary dictionaryWithObjects:lowcost forKeys:self.vendorsArray]; 
    NSDictionary *mr = [NSDictionary dictionaryWithObjects:midrange forKeys:self.vendorsArray]; 
    NSDictionary *he = [NSDictionary dictionaryWithObjects:highend forKeys:self.vendorsArray]; 
    NSDictionary *tk = [NSDictionary dictionaryWithObjects:trucks forKeys:self.vendorsArray]; 

    self.productFamiliesHash = [NSArray arrayWithObjects:lc,mr,he,tk,nil];
}

In gdb print-object results in this for productFamiliesHash:

(gdb) print-object self.productFamiliesHash
<__NSArrayI 0x6b2c760>(
{
    Toyota = "Corolla";
    Honda = "Fit";
},
{
    Toyota = "Camry";
    Honda = "Accord";
},
{
    Toyota = "Lexus";
    Honda = "Acura";
},
{
    Toyota = "Tacoma";
    Honda = "Ridgeline";
}
)

But, for the life of me I can't seem to access, for example, Toyota Corolla, which I would expect I could do like this in gdb:

(gdb) p [[productFamiliesHash objectAtIndex:0] objectForKey:@"Toyota"]

However, gdb gives:

Unable to call function "objc_msgSend" at 0x156408c: no return type information available.

How do I dereference the dictionary within the array?

You have it right. Try po in the gdb console instead of p. po prints out ObjC objects. — Alex Wayne
– Alex Wayne, Commented Jan 25, 2012 at 4:57
You probably should avoid using the name productFamiliesHash when the object is really an array. — ThomasW
– ThomasW, Commented Jan 25, 2012 at 5:47

iccir · Accepted Answer · 2012-01-25 04:57:46Z

4

Try using po instead of p. For Objective-C methods, p requires that you cast the result:

(gdb) p (id) [[productFamiliesHash objectAtIndex:0] objectForKey:@"Toyota"]

Even then, you won't get the description of the object, only the pointer value.

answered Jan 25, 2012 at 4:57

iccir

5,1383 gold badges24 silver badges34 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Sly Over a year ago

Awesome. Thanks @iccir. Works like a charm! (using the po)

Costique · Accepted Answer · 2012-01-25 05:00:36Z

1

Use po (print object) instead. The other important thing is that gdb needs to know the exact type of object before it can send it a message directly, so you just have to cast it properly:

po [(NSDictionary *)[productFamiliesHash objectAtIndex:0] objectForKey:@"Toyota"]

answered Jan 25, 2012 at 5:00

Costique

23.7k4 gold badges78 silver badges79 bronze badges

5 Comments

ThomasW Over a year ago

Actually, in this case you don't need to cast it. iccir's way works fine.

Aram Kocharyan Over a year ago

for that matter, it might generate a warning in code if you didn't cast and sent a message to an (id)?

Sly Over a year ago

Thanks for the quick response @Costique. I gave this one to iccir, just because he was first...

Costique Over a year ago

@ThomasW Hm, doesn't "no return type information available" say that gdb can't guess the return type of [productFamiliesHash objectAtIndex:0] because it is declared as id?

ThomasW Over a year ago

@Costique I just tried and gdb doesn't give that message in this case, even if productFamiliesHash is of type id. I think the case where it does give the "no return type information available" message is when the return type is not known to be an objective-C object.

Collectives™ on Stack Overflow

Accessing an array of dictionaries in Objective-C

2 Answers 2

1 Comment

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related