Cocoa Touch UITableView Alphabetical ‘#’ Match All Unmatched

In this article, we’ll explore a common requirement for UITableView developers: grouping and sorting objects by their first letter. We’ll also delve into matching any section (‘A’-‘Z’) using the ‘#’ symbol.

Understanding the Problem

When displaying a list of objects in a UITableView, it’s often necessary to group them by their first letter or character. This can be particularly useful when displaying names, addresses, or other types of data that have a common prefix.

In this example, we’re dealing with a specific use case where we want to match any section (‘A’-‘Z’) using the ‘#’ symbol. The problem arises when trying to include the ‘#’ symbol in our matching pattern, as it doesn’t conform to traditional alphabetical characters.

Solution Overview

To solve this issue, we’ll be utilizing a combination of UILocalizedIndexedCollation and a custom array category. We’ll also use a decorator for UILocalizedIndexedCollation to handle search functionality.

Using UILocalizedIndexedCollation

UILocalizedIndexedCollation is a class that provides an efficient way to index and group objects based on their localized values. When using this class, we can take advantage of the built-in logic for indexing and grouping objects in a localized manner.

#import <Foundation/Foundation.h>

// Create a UILocalizedIndexedCollation instance.
UILocalizedIndexedCollation *collation = [UILocalizedIndexedCollation currentCollation];

Custom Array Category

To create an indexed array of our objects, we’ll need to implement a custom array category. This category will provide a method for indexing objects based on their localized values using UILocalizedIndexedCollation.

#import <Foundation/Foundation.h>

// Declare the array category protocol.
@protocol MyArrayCategory <NSObject>
@required
- (NSArray *)indexUsingCollation:(UILocalizedIndexedCollation *)collation withSelector:(SEL)selector;
@end

// Implement the array category.
@interface NSArray (MyArrayCategory)

#pragma mark - Indexing

- (NSArray *)indexUsingCollation:(UILocalizedIndexedCollation *)collation withSelector:(SEL)selector {
    // Create an indexed array based on UILocalizedIndexedCollation's index method.
    return [self indexSetWithDictionary:[self indicesForSelector:selector] collation:collation];
}

#pragma mark - Indices

- (NSDictionary *)indicesForSelector:(SEL)selector {
    // Get the localized values for each object in the array.
    NSMutableDictionary *localizationMap = [NSMutableDictionary dictionary];
    
    for (id obj in self) {
        NSString *localizedValue = [self localizedStringForObject:obj selector:selector];
        
        if (!localizationMap[localizedValue]) {
            localizationMap[localizedValue] = [];
        }
        
        NSMutableArray *objectArray = [localizationMap[localizedValue] mutableCopy];
        [objectArray addObject:obj];
        
        localizationMap[localizedValue] = objectArray;
    }
    
    return localizationMap;
}

#pragma mark - Localization

- (NSString *)localizedStringForObject:(id)object selector:(SEL)selector {
    // Use the UILocalizedIndexedCollation's localizedString method to get the localized string for each object.
    NSString *localizedString = [UILocalizedIndexedCollation localizedStringForKey:object selector:selector];
    
    return localizedString;
}

@end

Collation Decorator

To handle search functionality, we’ll create a decorator class that wraps UILocalizedIndexedCollation. This decorator will include the search symbol and provide offsets for searching.

#import <Foundation/Foundation.h>

// Create a collation decorator instance.
@interface MyUILocalizedIndexedCollation : UILocalizedIndexedCollation

#pragma mark - Search Symbol

- (void)addSearchSymbol:(NSString *)symbol {
    [self addLocalizedKeyPath:@"search" value:symbol];
}

#pragma mark - Offsets

- (NSArray *)offsetsForSearching:(NSString *)searchString {
    // Get the offset for searching using UILocalizedIndexedCollation's index method.
    return [self indexUsingCollation:collation withSelector:@selector(name)];
}

@end

Using the Decorator

To use the decorator, we’ll create an instance of MyUILocalizedIndexedCollation and pass it to our array category.

#import <Foundation/Foundation.h>

// Create a MyUILocalizedIndexedCollation instance.
MyUILocalizedIndexedCollation *collation = [[MyUILocalizedIndexedCollation alloc] init];

// Add the search symbol to the collation.
[collation addSearchSymbol:@"#"];

// Get the indexed array using the array category.
NSArray *indexedArray = [arr indexUsingCollation:collation withSelector:@selector(name)];

Conclusion

In this article, we explored a common requirement for UITableView developers: grouping and sorting objects by their first letter. We also delved into matching any section (‘A’-‘Z’) using the ‘#’ symbol.

By utilizing a combination of UILocalizedIndexedCollation and a custom array category, along with a decorator class for handling search functionality, we were able to efficiently index and group our objects in a localized manner.

Whether you’re working on a project that requires complex data sorting or simply need help with indexing your data, this solution provides a solid foundation for achieving your goals.

Last modified on 2025-02-23