iPhone – What are reuseIdentifiers (UITableViewCell)?

by

Ok, this is how I believe it works:

Using dequeueReusableCellWithIdentifier for the tableView, you can greatly speed things up. Instead of instantiating a lot of cells, you just instantiate as many as needed, i.e. as many that are visible (this is handled automatically). If scrolling to an area in the list where there are “cells” that haven’t got their visual representation yet, instead of instantiating new ones, you reuse already existing ones.

You can try this yourself by doing this:

static NSString *CellIdentifier = @"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

if (cell == nil)
{
    cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
    NSLog(@"new one");
}
else
{
    NSLog(@"old one");
}

Remember, you only want dequeueReusableCellWithIdentifier to return a cell if it is applicable. So if a cell is going to be reused, make sure it is correct for the situation. That’s what reuseIdentifiers are for. Usually, you will only need one. But there might be a list that uses several different kinds of cells, and in that case, you’d have to keep them separate by providing different reuseIdentifiers. Otherwise you might end up getting a cell that you treat as some other kind of cell (for example, UITableView cell instead of the custom one you wanted).

So basically, as I understand it, use different reuseIdentifiers for different kinds of cells, where kind means class. If you only use standard cells, you probably only need one reuseIdentifier.

This design pattern is known as object pooling.

More Related Contents:

  1. iPhone/iOS JSON parsing tutorial [closed]
  2. Lazy load images in UITableView
  3. UITableViewCell expand on click
  4. Select tableview row programmatically
  5. UITableView issue when using separate delegate/dataSource
  6. UIButton not showing highlight on tap in iOS7
  7. How to use the first character as a section name
  8. How do I make UITableViewCell’s ImageView a fixed size even when the image is smaller
  9. UITableView dequeueReusableCellWithIdentifier Theory
  10. iPhone – dequeueReusableCellWithIdentifier usage
  11. Last In-First Out Stack with GCD?
  12. How to give space between two cells in tableview?
  13. UITableView Scroll event
  14. How to scroll UITableView to specific position
  15. How to Start UITableView on the Last Cell?
  16. iPhone :UITableView CellAccessory Checkmark
  17. UITableView reload data
  18. How to use UITableView inside UIScrollView and receive a cell click?
  19. how to properly use insertRowsAtIndexPaths?
  20. UITableViewCell Accessory Type Checked on Tap & Set other unchecked
  21. Accessing UITextField in a custom UITableViewCell
  22. UISwitch in a UITableView cell
  23. iOS – Get CPU usage from application
  24. HTML Content fit in UIWebview without zooming out
  25. Can I access the keychain on the iPhone?
  26. Add a multiple buttons to a view programmatically, call the same method, determine which button it was
  27. How do I set recipients for UIActivityViewController in iOS 6?
  28. Issue With Code: Format string is not a string literal [duplicate]
  29. How to create a round button?
  30. Making a UIImage to a circle form

Leave a Comment