Cells vanishing and reappearing when scrolling a UITableView - ios

Question

I am having some odd behaviour with my UITableView. When I scroll up and down sometimes the bottom row will vanish and disappear again. Not sure why this is happening. Each of my UITableCells contains 4 buttons like so :
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"cell" forIndexPath:indexPath];
int x,y;
x=5;
y=0;
for(int i = (int)indexPath.row*4; i<(int)indexPath.row*4+4; i++) {
//make sure we don't hit a blank in the array
if(i<[self.buttons count]) {
UIButton *button = [[UIButton alloc] init];
button = self.buttons[i];
button.layer.cornerRadius = button.frame.size.width / 2;
button.clipsToBounds = YES;
[button setFrame:CGRectMake(x, y, 70, 70)];
[cell.contentView addSubview:button];
x+=80;
}
}
return cell;
}
Could this be because I have the same cell reuse identifier for each cell? Does it need to be unique?

Answer 1

In this code:
UIButton *button = [[UIButton alloc] init];
button = self.buttons[i];
You allocate and initialize a button and then reassign the variable to entry i of a buttons array. Was this meant to be something else?
Also you are adding buttons to the cell content as a subview. Cells are reused when you scroll, so you could easily be adding more than 4 buttons to a given cell which will be causing you display issues. When you dequeue a cell it could already have 4 buttons in it.
Can you not just have 4 buttons in the cell prototype, saving you all this effort in the code.

Answer 2

No, cell reuse identifier need to be constant for a tableView. However you should use is as a static variable.
Change to static NSString *cellID = [NSString stringWithFormat:#"cellID",indexPath.row]; instead of
NSString *cellID = [NSString stringWithFormat:#"cell%d",indexPath.row];
Also are you making any changes in willDisplayCell or didEndDisplayingCell delegate methods. If yes Plz post that code too.

Answer 3

Re-write like this:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"cell" forIndexPath:indexPath];
if (cell.contentView.subviews.count == 0) {
int x,y;
x=5;
y=0;
for (int i = 0; i < 4; i++) {
UIButton *button = [[UIButton alloc] init];
button = self.buttons[i];
button.layer.cornerRadius = button.frame.size.width / 2;
button.clipsToBounds = YES;
[button setFrame:CGRectMake(x, y, 70, 70)];
[cell.contentView addSubview:button];
x+=80;
}
}
return cell;
}

Answer 4

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *cellIdentifier=#"cell";
UITableViewCell *cell=[tableView dequeueReusableCellWithIdentifier:cellIdentifier];
if (cell==nil)
{
cell=[[UITableViewCell alloc]initWithStyle:UITableViewCellStyleValue1 reuseIdentifier:cellIdentifier];
return cell;
}
}