ADBBackgroundCells allow lazy loading for UITableViewCell objects performing a long time job in background without blocking the UI. NSInvocationOperation are used under the hood in place of GCD (Grand Central Dispatch) since operations put in a NSOperationQueue object can be canceled. This threading fashion allows optimized long scrolling where a lot of cells are displayed and immediately reused/disappeared, without the obligation to execute the job of no more visible cells. ADBBackgroundCells are block-based and use Objective-C runtime.

If you'd like to include this component as a pod using CocoaPods, just add the following line to your Podfile: pod "ADBBackgroundCells"

Try out the included demo project.

Usage:

• copy UITableViewCell+Background.{h|m} and UITableView+Background.{h|m} into your project
• import UITableView+Background.h and UITableViewCell+Background.h in your code
• implement tableView:cellForRowAtIndexPath: similarly as follows:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *reuseCellId = @"reuseCellId";
    MyUITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:reuseCellId];
    if (!cell) {
        cell = [[MyUITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:reuseCellId];
    }

    NSMutableDictionary *info = [NSMutableDictionary dictionary];

    [cell addBackgroundBlock:^{
        // long time job performed on a background thread
        ...
        [info setObject:@"Long job output" forKey:@"output"];
    } callbackBlock:^(id cell){
        MyUITableViewCell *c = (MyUITableViewCell *)cell;
        // callback to update the UI
        c.textLabel.text = [info objectForKey:@"output"];
        ...
    } usingQueue:tableView.operationQueue];

    return cell;
}

• last but not least, create a NSOperationQueue in a safe place (the viewDidLoad method or the designated initializer of the controller containing the table view)

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.tableView.operationQueue = [[NSOperationQueue alloc] init];
    self.tableView.operationQueue.maxConcurrentOperationCount = 1;
    ...
}

License

Licensed under the New BSD License.

Copyright (c) 2012, Alberto De Bortoli All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. * Neither the name of Alberto De Bortoli nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL Alberto De Bortoli BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Resources

Info can be found on my website, and on Twitter.