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.