When to remove subview from UITableViewCell? - ios

Question

I have a UITableView with searchBar and searchDisplayController. What I wanted to do was to show a button when no results were found. So user could search server's database. I have a NSMutableArrayto store searchResults. So my delegate method looks like this:
- (void)filterContentForSearchText:(NSString*)searchText scope:(NSString*)scope
{
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"titulo contains [cd] %#", searchText];
NSArray *filtroUsuario = [self.objects filteredArrayUsingPredicate:predicate];
self.searchResults = [[NSMutableArray alloc] initWithArray:filtroUsuario];
if (self.searchResults.count < 1) {
UIButton *btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
btn.frame = CGRectMake(0, 0, 320, 50);
btn.showsTouchWhenHighlighted = YES;
[btn setTitle:#"Procurar no Banco de Dados" forState:UIControlStateNormal];
btn.tag = 1;
[self.searchResults addObject:btn];
self.adicionar = YES;
}
}
Basically, when there are no results, I create and add a buttonto my results array. Then, in cellForRowAtIndexPath, I have the following:
if (tableView == self.searchDisplayController.searchResultsTableView) {
if (self.adicionar == YES) {
cell.textLabel.text = #"";
[cell.contentView addSubview:self.searchResults[indexPath.row]];
self.adicionar = NO;
}
This shows the buttonexactly the way I want, and when cancelButtonis pressed, or the buttonin question, I just remove it from searchResultsin case user searches again. [self.searchResults removeAllObjects].
The problem was that, since I'm reusing cells, the subview was still there when user searched again. I had a few options to deal with this, I could create a property for the cell and remove subview when buttonwas pressed. But I opted to include the line [[cell.contentView viewWithTag:1] removeFromSuperview];at the beginning of cellForRowAtIndexPath, so when it's called again, it deletes the subViewsbefore continue.
Everything works perfectly now. My question is if this is the best approach or if there's something more simple. Since my app is a complex app, I'm very concerned about memory and performance, besides, I would really like to learn the coolest techniques available.
Any thoughts?

Answer 1

take a look at -prepareForReuse on the UITableViewCell. Probably the best fit for the exact situation you describe. (sketched example below)
#interface CustomCellName : UITableViewCell
#property (strong, nonatomic) UIButton *someButton;
#end
#implementation
- (void)prepareForReuse
{
_someButton.hidden = YES;
//etc...
}
#end
Tags are also perfectly fine, although many people find that approach to be unsatisfying. (*citation needed)
An alternate approach is to subclass UITableViewCell with a UIButton as a property which you can tweak from the tableView by -cellForRowAtIndexPath.

Answer 2

Best is a flexible term - best in what regard...
What you have works, but it isn't a good allocation of responsibility. It would be better to create a custom cell subclass and have it provide an API where a custom button can be added. The cell subclass would handle cleanup of the button in prepareForReuse.
From a memory and performance point of view there is little difference. But using a cell subclass is more correct.
For performance, it's better not to create and destroy button instances. So, it would be better for your cell subclass to create a button but keep it hidden until it's needed, then show it. Now, prepareForReuse would simply hide the button. Generally this would use a little more memory on average - it's a trade off...

Answer 3

First thing, mixing controls with your app data is not a good practice. You can make it work as you already have, but in long term trie to separate UI from application data. Table view should do all the work of presenting data and controls that manipulate your data so it is probably better idea to add string "No Data" to your result array and then handle it in cellForRowAtIndexPath. Create a button on your cell and just hide/show it when you need it. Don't worry about memory consumption, the cells are reusable so you will have very small number of buttons (hidden ones).
Second thing if you really wont to create only one button then tag it, for example, when you decide you need it create it and tag it with say 1000. Then later when you reload and don't want to show it, just ask your cell if it has a view with tag == 1000 and remove it from superview. But again it is an overkill and your memory integrity wont be endangered if you create one button for every visible cell.