objectForKey error with NSXMLParser - objective-c

Question

I'm getting the following error:
"this class is not key value coding-compliant for the key temp_f"
my AppDelegate class files:
#import <Cocoa/Cocoa.h>
#interface AppDelegate : NSObject <NSApplicationDelegate> {
IBOutlet NSTableView *tableView;
NSArray *current;
}
#property (assign) IBOutlet NSWindow *window;
#end
#import "AppDelegate.h"
#import "CurrentWeather.h"
#import "XMLCurrent.h"
#implementation AppDelegate
#synthesize window = _window;
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
XMLCurrent *currentXML = [[XMLCurrent alloc] init];
NSError *error = nil;
current = [currentXML fetchCurrentWithError:&error];
[tableView reloadData];
}
- (NSInteger)numberOfRowsInTableView:(NSTableView *)theTableView {
return [current count];
}
- (id)tableView:(NSTableView *)theTableView objectValueForTableColumn:(NSTableColumn *)tableColumn row:(NSInteger)row {
CurrentWeather *c = [current objectAtIndex:row];
return [c valueForKey:[tableColumn identifier]];
}
#end
my CurrentWeather class files:
#import <Foundation/Foundation.h>
#interface CurrentWeather : NSObject {
NSString *location;
NSString *weather;
NSString *degreesF;
}
#property (nonatomic, copy) NSString *location;
#property (nonatomic, copy) NSString *weather;
#property (nonatomic, copy) NSString *degreesF;
#end
#import "CurrentWeather.h"
#implementation CurrentWeather
#synthesize location, weather, degreesF;
#end
my XMLCurrent class files:
#import <Foundation/Foundation.h>
#interface XMLCurrent : NSObject <NSXMLParserDelegate> {
NSMutableArray *current;
NSMutableString *currentString;
NSMutableDictionary *currentFields;
}
- (NSArray *)fetchCurrentWithError:(NSError **)outError;
#end
#import "XMLCurrent.h"
#import "CurrentWeather.h"
#implementation XMLCurrent
- (id)init {
self = [super init];
if (self) {
current = [[NSMutableArray alloc] init];
}
return self;
}
- (NSArray *)fetchCurrentWithError:(NSError **)outError {
BOOL success;
NSURL *xmlURL = [NSURL URLWithString:#"http://www.weather.gov/xml/current_obs/KCLT.xml"];
NSURLRequest *req = [NSURLRequest requestWithURL:xmlURL cachePolicy:NSURLRequestReturnCacheDataElseLoad timeoutInterval:30];
NSURLResponse *resp = nil;
NSData *data = [NSURLConnection sendSynchronousRequest:req returningResponse:&resp error:outError];
if (!data) {
return nil;
}
[current removeAllObjects];
NSXMLParser *parser;
parser = [[NSXMLParser alloc] initWithData:data];
[parser setDelegate:self];
success = [parser parse];
if (!success) {
*outError = [parser parserError];
return nil;
}
NSArray *output = [current copy];
return output;
}
- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName
namespaceURI:(NSString *)namespaceURI
qualifiedName:(NSString *)qName
attributes:(NSDictionary *)attributeDict {
if ([elementName isEqual:#"current_observation"]) {
currentFields = [[NSMutableDictionary alloc] init];
}
}
- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName
namespaceURI:(NSString *)namespaceURI
qualifiedName:(NSString *)qName {
if ([elementName isEqual:#"current_observation"]) {
CurrentWeather *currentCond = [[CurrentWeather alloc] init];
[currentCond setLocation:[currentFields objectForKey:#"location"]];
[currentCond setWeather:[currentFields objectForKey:#"weather"]];
[currentCond setDegreesF:[currentFields objectForKey:#"temp_f"]];
[current addObject:currentCond];
currentCond = nil;
currentFields = nil;
} else if (currentFields && currentString) {
NSString *trimmed;
trimmed = [currentString stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
[currentFields setObject:trimmed forKey:elementName];
}
currentString = nil;
}
- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string {
if (!currentString) {
currentString = [[NSMutableString alloc] init];
}
[currentString appendString:string];
}
#end
The keys are used as the "identifier" in a table view. For some reason, if the key has an underscore in it (such as temp_f) I get an error. The underscore is necessary because it is the name of the element in the XML file. If there is no underscore, then no error. How can I get data from an XML element that contains an underscore?
The xml data is being parsed from http://www.weather.gov/xml/current_obs/KCLT.xml

Answer 1

CurrentWeather has a degreesF property, which you set from the temp_f XML field. You need to set the identifier for the table column to "degreesF" not "temp_f". This has nothing to do with temp_f containing an underscore. Rather, the problem is that CurrentWeather isn't Key Value Coding compliant for the key "temp_f" (just as the error states) because it doesn't have a property named "temp_f".
Explaining in further detail, in your -tableView:objectValueForTableColumn: method, you use the column's identifier as a key into a CurrentWeather instance. Since the identifier is "temp_f", you're doing this: [c valueForKey:#"temp_f"]. That throws an exception because CurrentWeather doesn't have a temp_f property.