IOS: Stop cells being incorrectly reused in UITableView - ios

Question

I have a basic UITableView with four sections. I control the content in each section with a Switch statement.
I programmatically create a button, which should appear in the rows of the first THREE sections, but should NOT appear in the fourth. However, the button is appearing randomly in the fourth section's rows.
I presume this is because a cell is being reused, but as I create each section's rows with the Switch statement, I cannot see how this is happening. Any ideas appreciated.
I am using a custom cell configured so:`
static NSString *CustomCellIdentifier = #"DashboardCell";
DashboardCell *cell = (DashboardCell *)[tableView dequeueReusableCellWithIdentifier: CustomCellIdentifier];
if (cell == nil) { NSArray *nib = [[NSBundle mainBundle] loadNibNamed:#"DashboardCell"
owner:self options:nil];
for (id oneObject in nib) if ([oneObject isKindOfClass:[DashboardCell class]])
cell = (DashboardCell *)oneObject;
}
// Configure the cell.`
The code to create this button is: `
button = [UIButton buttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(200, 11, 50, 50);
UIImage *iConnect = [UIImage imageNamed:#"connect.png"];
[button setImage:iConnect forState:UIControlStateNormal];
[button addTarget:self action:#selector(buttonSelected:) forControlEvents:UIControlEventTouchUpInside];
[cell addSubview:button];`

Answer 1

You need a different reuse identifier for each type of content. So here you have two types of content - cell's that have a UIButton and cells that don't.
Use the indexPath of the tableView:cellForRowAtIndexPath: method to select a reuse identifier of either #"CellWithButton" or #"CellWithoutButton".
What is actually happening in your code is that all cells are given the same reuse identifier, meaning that they all get put into the same object pool. This means that when you use [tableView dequeueReusableCellWithIdentifier: CustomCellIdentifier]; that you are retrieving a cell from this one pool (which potentially contains cells that have no UIButton and cells that do). Therefore the dequeue method can randomly return a cell that has already had a UIButton added to it. If you use two reuse identifiers, the UITableView will setup two object pools and will correctly deposit and retrieve the appropriate cells from each.
Or you can use one reuse pool and check the cell for a UIButton each time you retrieve one using the dequeue method.

Answer 2

In your DashboardCell, create a property #property (nonatomic, assign) BOOL buttonEnabled. Then in your awakeFromNib, always create the button and set button.hidden = YES. Override the setter of your property
- (void)setButtonEnabled:(BOOL)enabled {
buttonEnabled = enabled;
button.hidden = !enabled;
}
And finally override prepareForReuse
- (void)prepareForReuse {
[super prepareForReuse];
self.buttonEnabled = NO;
}
And now you can enbale/disable in your configure part of the method cellForRowAtIndexPath

Answer 3

You can use two different cell identifiers depending on the section. Otherwise you would need to see whether the button existed in the cell that's returned from dequeueReusableCellWithIdentifier: and add one or remove an existing one if necessary.

Answer 4

If you're going to be reusing these cells and there's some simple logic behind showing or hiding each cell's button the first thing I would recommend is that you create the button in Interface Builder and connect it as an outlet to your UITableViewDelegate.
I would then create a setup method for the cell that you can run at any time, any number of times without it breaking it:
-(UITableViewCell*)tableView:(UITableView*)tableView cellForRowAtIndexPath:(NSIndexPath*)indexPath
{
static NSString *CustomCellIdentifier = #"DashboardCell";
DashboardCell *cell = (DashboardCell *)[tableView dequeueReusableCellWithIdentifier: CustomCellIdentifier];
if (cell == nil) { NSArray *nib = [[NSBundle mainBundle] loadNibNamed:#"DashboardCell"
owner:self options:nil];
for (id oneObject in nib) if ([oneObject isKindOfClass:[DashboardCell class]])
cell = (DashboardCell *)oneObject;
}
// Configure the cell.
[cell setupWithSomeConfigOptions:someConfigOptions]
return cell;
}
And in your cell subclass you would have the method -(void)setupWithSomeOptions:(SomeOptions)someOptions, which would be something along the lines of:
-(void)setupWithSomeOptions:(SomeOptions)someOptions
{
// some setup code
self.myButtonOutlet.hidden = someOptions.somePropertyToCheckIfButtonShouldBeHidden;
// some more setup code
}