Storing Multiple Selections in Sectioned UITableView

As developers, we’ve all been there - faced with a complex problem that requires creative solutions. In this article, we’ll delve into the world of sectioned UITableViews and explore how to store multiple selections within it.

Understanding the Problem

We’re given a list of people in a UITableView, sectioned by the first letter of their names. Our goal is to allow users to select multiple individuals from this list, with a checkbox next to each name. However, we need a reliable way to store and retrieve these selections, taking into account both section and row indices.

The Challenge

Before diving into solutions, let’s discuss the challenges involved:

• Using NSMutableArray or multidimensional arrays doesn’t seem suitable for storing selections due to their limitations.
• Saving data to a database might be overkill, especially since we don’t need persistent data.
• We want a system that allows efficient storage and retrieval of selection states.

A Solution: Using NSDictionary

After extensive research, our developer decided to use an NSMutableDictionary to store selections. The key to this solution lies in constructing the dictionary key from both section and row indices. Let’s break it down:

• Cell Identifier: We create a unique string for each cell based on its section and row numbers: "Cell-%i-%i". This will serve as our dictionary key.
• Storing Selections: When setting the selection, we use the constructed cell identifier as the key and store a boolean value representing the selection state (BOOLselected).

Here’s the code snippet:

- (void) setSelected:(NSMutableDictionary*)dict forIndexPath:(NSIndexPath*)indexPath withValue:(BOOL)selected{
    NSString *cellIdentifier = [NSString stringWithFormat:@"Cell-%i-%i", (int)indexPath.section, (int)indexPath.row];

    [dict setObject:[NSNumber numberWithBool:selected] forKey:cellIdentifier];
}

• Retrieving Selections: When getting the selection state, we use the same cell identifier to retrieve the corresponding boolean value from the dictionary.

- (BOOL) getSelected:(NSMutableDictionary*)dict forIndexPath:(NSIndexPath*)indexPath {
    NSString *cellIdentifier = [NSString stringWithFormat:@"Cell-%i-%i", (int)indexPath.section, (int)indexPath.row];
    BOOL selected=[[dict objectForKey:cellIdentifier]  boolValue];

    return selected;
}

• Toggling Selections: To toggle the selection state, we simply invert the boolean value and re-store it in the dictionary using setSelected.

- (BOOL) toggleSelected:(NSMutableDictionary*)dict forIndexPath:(NSIndexPath*)indexPath {
    NSString *cellIdentifier = [NSString stringWithFormat:@"Cell-%i-%i", (int)indexPath.section, (int)indexPath.row];

    BOOL selected=[[dict objectForKey:cellIdentifier]  boolValue];
    selected=!selected;

    [self setSelected:dict forIndexPath:indexPath withValue:selected];

    return selected;
}

Benefits and Considerations

Using an NSMutableDictionary offers several benefits:

• Efficient Storage: The dictionary allows for efficient storage and retrieval of selection states, taking into account both section and row indices.
• Simple Code: This implementation is straightforward and easy to understand.

However, there are some considerations to keep in mind:

• Dictionary Performance: Using an NSMutableDictionary might lead to slower performance compared to other data structures. However, for a table view with multiple selections, this may not be a significant concern.
• Memory Management: As the user interacts with the list, the dictionary will grow and shrink dynamically. Make sure to handle memory management accordingly.

Conclusion

Storing multiple selections in a sectioned UITableView is a challenging task that requires creative problem-solving. By leveraging an NSMutableDictionary, we can efficiently store and retrieve selection states while maintaining code simplicity. While there are some considerations to keep in mind, this solution provides a solid foundation for building robust table views with complex selection mechanisms.

Example Use Cases

Here’s an example of how you might use the provided code snippets:

// Initialize an NSMutableDictionary to store selections

NSMutableDictionary *selections = [[NSMutableDictionary alloc] init];

// Set the selection state for a specific cell

NSIndexPath *indexPath = [NSIndexPath indexPathForRow:0 inSection:0];
[self setSelected:selections forIndexPath:indexPath withValue:YES];

// Get the selection state for a specific cell

indexPath = [NSIndexPath indexPathForRow:1 inSection:1];
BOOL selected = [self getSelected:selections forIndexPath:indexPath];
if (selected) {
    NSLog(@"Cell selected!");
} else {
    NSLog(@"Cell not selected.");
}

// Toggle the selection state for a specific cell

indexPath = [NSIndexPath indexPathForRow:2 inSection:0];
[self toggleSelected:selections forIndexPath:indexPath];

Last modified on 2023-07-24