"Drink Mixer" Example Head First iPhone & iPad Development - iphone

Question

i'm kinda new to Objective-C so i have been learning with the Head First iPhone & iPad Development book. In this book, at the Chapter 4-5 you suppose to design an app for a bartender, that basically is a table view of a list of drinks with the details list (it suppose to have the ingredients and directions for the drink selected). The data comes from two property lists, one has a list of strings with the names of the drinks, and the other is a Dictionary that has the name, directions and ingredients of the drinks.
I have followed the tutorial and the app crashes, re-checked it and still crashes. I'm using an Xcode Version of 4.0.1 and MAC OS X 10.6.8.
Here is the exception, i hope that you guys can check out what happens at this simple application.
2012-07-19 21:43:39.757 DrinkMixer[846:207] -[NSCFString objectForKey:]: unrecognized selector sent to instance 0x4b31220
2012-07-19 21:43:39.761 DrinkMixer[846:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSCFString objectForKey:]: unrecognized selector sent to instance 0x4b31220'
*** Call stack at first throw:
(
0 CoreFoundation 0x00dc25a9 __exceptionPreprocess + 185
1 libobjc.A.dylib 0x00f16313 objc_exception_throw + 44
2 CoreFoundation 0x00dc40bb -[NSObject(NSObject) doesNotRecognizeSelector:] + 187
3 CoreFoundation 0x00d33966 ___forwarding___ + 966
4 CoreFoundation 0x00d33522 _CF_forwarding_prep_0 + 50
5 DrinkMixer 0x00002495 -[RootViewController tableView:cellForRowAtIndexPath:] + 325
6 UIKit 0x00089b98 -[UITableView(UITableViewInternal) _createPreparedCellForGlobalRow:withIndexPath:] + 634
7 UIKit 0x0007f4cc -[UITableView(UITableViewInternal) _createPreparedCellForGlobalRow:] + 75
8 UIKit 0x000948cc -[UITableView(_UITableViewPrivate) _updateVisibleCellsNow:] + 1561
9 UIKit 0x0008c90c -[UITableView layoutSubviews] + 242
10 QuartzCore 0x016aca5a -[CALayer layoutSublayers] + 181
11 QuartzCore 0x016aeddc CALayerLayoutIfNeeded + 220
12 QuartzCore 0x016540b4 _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 310
13 QuartzCore 0x01655294 _ZN2CA11Transaction6commitEv + 292
14 UIKit 0x000169c9 -[UIApplication _reportAppLaunchFinished] + 39
15 UIKit 0x00016e83 -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 690
16 UIKit 0x00021617 -[UIApplication handleEvent:withNewEvent:] + 1533
17 UIKit 0x00019abf -[UIApplication sendEvent:] + 71
18 UIKit 0x0001ef2e _UIApplicationHandleEvent + 7576
19 GraphicsServices 0x00ffb992 PurpleEventCallback + 1550
20 CoreFoundation 0x00da3944 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 52
21 CoreFoundation 0x00d03cf7 __CFRunLoopDoSource1 + 215
22 CoreFoundation 0x00d00f83 __CFRunLoopRun + 979
23 CoreFoundation 0x00d00840 CFRunLoopRunSpecific + 208
24 CoreFoundation 0x00d00761 CFRunLoopRunInMode + 97
25 UIKit 0x000167d2 -[UIApplication _run] + 623
26 UIKit 0x00022c93 UIApplicationMain + 1160
27 DrinkMixer 0x00001c89 main + 121
28 DrinkMixer 0x00001c05 start + 53
)
terminate called after throwing an instance of 'NSException'
sharedlibrary apply-load-rules all
(gdb)
And here is exactly when the app crashes, at the objectForKey:#"name"
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
}
cell.textLabel.text = [[self.drinks objectAtIndex:indexPath.row] objectForKey:#"name"];
return cell;
}

Answer 1

the clue in the first line of the error is that you have initialized the contents of self.drinks at the index that corresponds to indexPath.row to be an NSString. when that objectAtIndex: is retrieved, it is then passed the message objectForKey: as though it is an NSArray.
look at the code where you've initialized self.drinks and make certain you've made it an appropriate array containing appropriate contents. in your case, it would be an array of NSDictionary* for objectForKey: to work).

Answer 2

Debug your code and check drinks is an array of NSDictonary.