<objc/runtime.h> example

objc_runtime_example.mm

//
//  BFViewController.m
//  ObjcRuntimeExample
//
//  Created by Mark Joslin on 3/26/13.
//  Copyright (c) 2013 BitFountain. All rights reserved.
//

#import <objc/runtime.h>
#import "BFTableViewControler.h"

// Example user object
@interface User : NSObject
@property int id;
@end
@implementation User
@end

@interface BFTableViewControler ()
@end

@implementation BFTableViewControler
{
    NSArray *_users;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    // Init our fake users
    User *user = [[User alloc] init];
    user.id = 1;
    User *user1 = [[User alloc] init];
    user1.id = 2;
    User *user2 = [[User alloc] init];
    user2.id = 3;
    _users = @[user, user1, user2];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    // Return the number of sections.
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    // Return the number of rows in the section.
    return _users.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (!cell) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
    }
    
    // Configure the cell with a tap gesture recognizer on the cell's text label
    User *user = _users[indexPath.row];
    cell.textLabel.text = [NSString stringWithFormat:@"User %d", user.id];
    cell.textLabel.font = [UIFont fontWithName:@"Helvetica" size:20.0f];
    cell.textLabel.backgroundColor = [UIColor colorWithWhite:0.8f alpha:0.5f];
    
    // Now let's associate the cell with the user & cell properties on a gesture recognizer to demonstrate
    // how you can chain along attributes this way.
    UITapGestureRecognizer *tapGestureRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(didSelectCellTextLabel:)];
    objc_setAssociatedObject(tapGestureRecognizer, @"user", user, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    objc_setAssociatedObject(tapGestureRecognizer, @"cell", cell, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    [cell addGestureRecognizer:tapGestureRecognizer];
    
    return cell;
}

- (void)didSelectCellTextLabel:(UITapGestureRecognizer *)tapGestureRecognizer
{
    // get the user & text properties
    User *user = objc_getAssociatedObject(tapGestureRecognizer, @"user");
    UITableViewCell *cell = objc_getAssociatedObject(tapGestureRecognizer, @"cell");
    cell.textLabel.text = [NSString stringWithFormat:@"%d user", user.id];
    
    assert(user.id > 0);
    assert(cell != nil);
    NSLog(@"hooray, we've passed metadata inside of our callback object");
}

#pragma mark - Table view delegate

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
}

@end