Parsing XML Feed with Objective-C: A Case Study on Stock Values

In this article, we will delve into the world of Objective-C parsing, focusing on XML feeds as a case study for stock values. We will explore the common pitfalls and mistakes that can occur during parsing and provide practical advice on how to improve code quality.

Introduction

Objective-C is a powerful programming language used primarily for developing iOS, macOS, watchOS, and tvOS apps. When it comes to parsing XML feeds, developers often face challenges due to the complexity of XML structures and the nuances of Objective-C syntax. In this article, we will examine a specific example from Stack Overflow, highlighting common mistakes and providing guidance on how to correct them.

Understanding the Problem

The original code snippet presented is written in Objective-C, and it appears to be intended for parsing an XML feed containing stock values. The goal is to extract the relevant data and store it in an array for further processing.

Code Review

Upon reviewing the provided code, we notice several issues:

1. Incorrect Method Calls: In the parser:didEndElement: method, there’s a typo in the method call [currency setvalue:[[elencoFeed Objectatindex:i] valueforkey:@"rate"] forkey:[[elencoFeed Objectatindex:i] valueforkey:@"currency"]]. The correct signature is objectAtIndex: and valueForKey:.
2. Type Inconsistency: The variable currency is declared as an instance of NSArray, which does not have a text property. This inconsistency will cause a compilation error when trying to access currency.text.

Correcting the Code

To fix these issues, we need to correct the method calls and ensure type consistency.

- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName{
    if ([elementName isEqualToString:@"Cube"]) {
        /* salva tutte le proprietà del feed letto nell'elemento "item", per 
         poi inserirlo nell'array "elencoFeed" */
        [item setObject:currentCube forKey:@"Cube"];

        [elencoFeed addObject:[item copy]];
    }
}

- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string{
    // salva i caratteri per l'elemento corrente
    if ([currentElement isEqualToString:@"Cube"]){
        [currentCube appendString:string];
    }
}

- (void)viewDidLoad {
    [super viewDidLoad];
    convertisseur = [[Convertisseur alloc] init];

    self.title = @"Convertisseur";

    NSString *path = @"http://www.ecb.int/stats/eurofxref/eurofxref-daily.xml";
    [self parseXMLFileAtURL:path];

    // Use the correct index to access the array
    int index = 0;
    if (index < elencoFeed.count) {
        id value = [elencoFeed objectAtIndex:index];
        NSString *rate = [(NSDictionary *)value objectForKey:@"rate"];
        NSString *currency = [(NSDictionary *)value objectForKey:@"currency"];

        euro.text = rate;
    }
}

Additional Advice

1. Use English as the Primary Language: While it’s okay to use your native language in code comments or documentation, it’s recommended to stick with English in your main code for better readability and maintainability.
2. Be Mindful of Type Inconsistencies: Ensure that variable declarations and method calls are consistent in terms of data types.

Conclusion

In this article, we examined a specific example from Stack Overflow, highlighting common mistakes when parsing XML feeds with Objective-C. By correcting the code and following best practices, developers can improve code quality and avoid potential pitfalls. Remember to use English as the primary language, be mindful of type inconsistencies, and strive for clarity in your code.

Last modified on 2024-07-12