How to expand and collapse rows using header section in a UITableView

Question

I have a table view. Now I want to collapse and expand rows by tapping on the section header. In other words, when I tap the header the rows display for that section. How ca

Answer 1

I draft up some code to give you the idea. The concept is we keep track of collapsed section in NSMutableSet and add/remove it according to the user touch on the section. The collapse/expand animation is actually the animation of adding/removing cells.

#import "ViewController.h"

@interface ViewController () < UITableViewDataSource, UITableViewDelegate> {
    NSMutableSet* _collapsedSections;
}

@property (nonatomic, weak) IBOutlet UITableView* tableView;

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    _collapsedSections = [NSMutableSet new];
}

-(NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return 3;
}

-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return [_collapsedSections containsObject:@(section)] ? 0 : 10;
}

-(NSArray*) indexPathsForSection:(int)section withNumberOfRows:(int)numberOfRows {
    NSMutableArray* indexPaths = [NSMutableArray new];
    for (int i = 0; i < numberOfRows; i++) {
        NSIndexPath* indexPath = [NSIndexPath indexPathForRow:i inSection:section];
        [indexPaths addObject:indexPath];
    }
    return indexPaths;
}

-(void)sectionButtonTouchUpInside:(UIButton*)sender {
    sender.backgroundColor = [UIColor greenColor];
    [self.tableView beginUpdates];
    int section = sender.tag;
    bool shouldCollapse = ![_collapsedSections containsObject:@(section)];
    if (shouldCollapse) {
        int numOfRows = [self.tableView numberOfRowsInSection:section];
        NSArray* indexPaths = [self indexPathsForSection:section withNumberOfRows:numOfRows];
        [self.tableView deleteRowsAtIndexPaths:indexPaths withRowAnimation:UITableViewRowAnimationTop];
        [_collapsedSections addObject:@(section)];
    }
    else {
        int numOfRows = 10;
        NSArray* indexPaths = [self indexPathsForSection:section withNumberOfRows:numOfRows];
        [self.tableView insertRowsAtIndexPaths:indexPaths withRowAnimation:UITableViewRowAnimationTop];
        [_collapsedSections removeObject:@(section)];
    }
    [self.tableView endUpdates];
    //[_tableView reloadData];
}

-(UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section {
    UIButton* result = [UIButton buttonWithType:UIButtonTypeCustom];
    [result addTarget:self action:@selector(sectionButtonTouchUpInside:) forControlEvents:UIControlEventTouchUpInside];
    result.backgroundColor = [UIColor blueColor];
    [result setTitle:[NSString stringWithFormat:@"Section %d", section] forState:UIControlStateNormal];
    result.tag = section;
    return result;
}

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    UITableViewCell* result =  [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"cell"];
    result.textLabel.text = [NSString stringWithFormat:@"Cell %d", indexPath.row];
    return result;
}

@end