Setting NSString variables with NSXMLParser

Question

I am using NSXMLParser to grab information from an online XML file. My goal is to have one class do the XML parsing and another class to implement the variables. Below is the code for my project:

Current.h & Current.m

#import <Foundation/Foundation.h>

@interface Current : NSObject {
    NSString *curTempF;
    IBOutlet NSTextField *textField;
}

@property (nonatomic, copy) NSString *curTempF;

- (void)displayOutlets:(id)sender;

@end

and

#import "Current.h"

@implementation Current

@synthesize curTempF;

- (void)awakeFromNib {
    [self displayOutlets:self];
}

- (void)displayOutlets:(id)sender {
    [textField setStringValue:curTempF];
}

@end

XmlParser.h & XmlParser.m

#import <Foundation/Foundation.h>

@interface XmlParser : NSObject <NSXMLParserDelegate> {
    NSString *urlString;
    NSURL *url;
    NSMutableString *xmlString;
}

- (IBAction)fetchXML:(id)sender;

@end

and

#import "XmlParser.h"
#import "Current.h"

@implementation XmlParser

- (void)awakeFromNib {
    [self fetchXML:self];
}

- (IBAction)fetchXML:(id)sender {
    urlString = @"http://api.wunderground.com/api/***/conditions/q/28173.xml";
    url = [NSURL URLWithString:urlString];

    NSXMLParser *parser = [[NSXMLParser alloc] initWithContentsOfURL:url];
    [parser setDelegate:self];
    [parser parse];
}

- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict {

    if ([elementName isEqual:@"temp_f"]) {
        xmlString = [[NSMutableString alloc] init];
    }
}

- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName {

    if ([elementName isEqual:@"temp_f"]) {        
        Current *cTempF = [[Current alloc] init];
        [cTempF setCurTempF:xmlString];
    }
}

- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string {
    [xmlString appendString:string];
}

@end

When I run the program I am receiving an error about "Invalid parameter not satisfying: aString". It looks like the setStringValue for the IBOutlet is not working. Any suggestions?

score 0 · Answer 1 · answered Apr 26 '12 at 21:12

0

I suspect that when you initialize the Current class with [[Current alloc] init], it is trying to populate the textField with the curTempF string. However, the curTempF string is not initialized yet at that point until you call [cTempF setCurTempF:xmlString].

One approach would be to not display outlets in the Current class:

- (void)awakeFromNib {
    //[self displayOutlets:self];
}

Then, call the displayOutlets function in your parser:

if ([elementName isEqual:@"temp_f"]) {        
    Current *cTempF = [[Current alloc] init];
    [cTempF setCurTempF:xmlString];
    [cTempF displayOutlets:cTempF]; 
}

Alternately, you could keep your awakeFromNib code the same, but create an initWith method in your Current class, which may be cleaner:

- (id) initWithCurTemp:(NSString *)curTemp {
    self = [super init]; 

    if (self) { 
        self.curTempF = curTemp; 
    }

    return self; 
}

- (void)awakeFromNib {
    [self displayOutlets:self];
}

Then, your parser code would look like:

if ([elementName isEqual:@"temp_f"]) {        
    Current *cTempF = [[Current alloc] initWithCurTemp:xmlString];
}

answered Apr 26 '12 at 21:12

Chris Livdahl

4,662
2
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Well I tried both approaches but neither seem to work. I don't get any errors when the project is run but the IBOutlet doesn't update with the string value. – wigging Apr 26 '12 at 22:17
How is the Current class connected to your view? In interface builder do you have a view that has a Current on it? The reason I ask is that you need to specifically be updating the Current that is on the view. Simply doing Current *cTempF = [[Current alloc] init]; won't do anything if this instance of Current is not on the view. – Chris Livdahl Apr 26 '12 at 22:21
I set up the IBOutlet as I always have. In IB I set up an object with it's class as "Current" and connected the outlet to my "label" in the window. – wigging Apr 26 '12 at 22:51
Right, but I think in your parser the "Current" object you instantiate is not the same "Current" object that gets instantiated in the Nib. – Chris Livdahl Apr 26 '12 at 23:22
So how do I set the string value of the nstextfield outlet? When I place an nslog in the "Current" class, the string for "curTempF" displays correctly in the debugger. – wigging Apr 26 '12 at 23:28
When I place an IBOutlet in the XMLParser class everything works fine. But I'm trying to keep everything separate: parsing for the "XMLParser" class and everything else in the "Current" class. – wigging Apr 27 '12 at 00:02
One approach would be to have a view controller that talks to a Parser instance to get the information, which it then stores in a Current instance. I would have the text field be an instance variable on the view controller, or perhaps a view if you need custom view characteristics. – Chris Livdahl Apr 27 '12 at 00:59
@Gavin: You could create your “Current” object (such a strange name for an object that has nothing to do with electricity) in the nib and connect an outlet from the XmlParser to the Current. – Peter Hosey Apr 27 '12 at 01:05
@PeterHosey Peter, could you reply with an answer and some example code would help out too. Thanks again for your help. – wigging Apr 27 '12 at 01:11
@Gavin, btw, here's a fairly good tutorial with code: http://iphonebyradix.blogspot.com/2011/08/parsing-xml-using-nsxmlparser.html – Chris Livdahl Apr 27 '12 at 01:31
@ChrisLivdahl So i've posted another question relating to this using a more simple code example. Feel free to check out the question and add your answer. – wigging Apr 27 '12 at 19:42
@Gavin, what's the link to the question? – Chris Livdahl Apr 27 '12 at 23:54
@ChrisLivdahl Here's the link to the new question: [Setting variables in a different class in Cocoa](http://stackoverflow.com/questions/10356822/setting-variables-in-a-different-class-in-cocoa) – wigging Apr 27 '12 at 23:56

score 0 · Answer 2 · answered Apr 27 '12 at 01:16

0

You should create your Current in the nib, as you were doing, and not in code.

As for getting the parser (which I assume is in the same nib) to talk to the Current, create an outlet in the parser to point to the Current, and connect that outlet in the nib.

answered Apr 27 '12 at 01:16

Peter Hosey

95,783
15
211
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Sorry but I'm still confused. I can get an IBOutlet in the xmlparser class to work just fine but my goal is to not do it that way. I want all outlets to be in other class files. Could you provide some code or point to an applicable online example project? – wigging Apr 27 '12 at 01:29
@Gavin: What do you mean by “I want all outlets to be in other class files”? If you don't want an XmlParser to know about Currents (which is reasonable), you might set it up as a delegate protocol, but the XmlParser's delegate property would still be a delegate. If you don't want the XmlParser to talk directly to the Current, then you'll have to make it happen indirectly through a third object. – Peter Hosey Apr 27 '12 at 01:31
So i've posted another question relating to this using a more simple code example. Feel free to check out the question and add your answer. – wigging Apr 27 '12 at 19:41

Setting NSString variables with NSXMLParser

2 Answers2