How do I clear a cell completely when I reuse it? - objective-c

Question

When I call [table reloaddata];
The cells get redrawn with new data, but my UILabels get messed up because they are drawn over the old UILabels, so its a mess.
static NSString* PlaceholderCellIdentifier = #"PlaceholderCell";
UITableViewCell* cell = [tableView dequeueReusableCellWithIdentifier:PlaceholderCellIdentifier];
if (cell == nil)
{
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:PlaceholderCellIdentifier] autorelease];
cell.detailTextLabel.textAlignment = UITextAlignmentCenter;
cell.selectionStyle = UITableViewCellSelectionStyleNone;
cell.contentView.backgroundColor = [UIColor clearColor];
}
Is my Init of the cell.
I add a UILabel like so
UILabel *theDateLabel = [[UILabel alloc] initWithFrame:CGRectMake(140, 35,140, 20)];
[theDateLabel setBackgroundColor:[UIColor clearColor]];
[theDateLabel setTextColor:[UIColor lightGrayColor]];
[theDateLabel setText:[dateFormatter stringFromDate:theDate]];
[theDateLabel setFont:[UIFont fontWithName:#"TrebuchetMS-Bold" size:15]];
[cell addSubview:theDateLabel];
[theDateLabel release];
There are a few more labels in the cell, same thing.
What I would like to happen is that the old labels disappear from the cell so that they are no longer visible.

Answer 1

You should not add theDateLabel as a subview of cell. You should add it as a subview of cell.contentView.
As yuji suggests, one way to implement this is to create a subclass of UITableViewCell with a property for each custom subview. That way you can easily get to the date label of a reused cell to set its text for the new row.
Another common approach is to use the tag property that every UIView has. For example:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString* PlaceholderCellIdentifier = #"PlaceholderCell";
static const int DateLabelTag = 1;
UITableViewCell* cell = [tableView dequeueReusableCellWithIdentifier:PlaceholderCellIdentifier];
if (!cell) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:PlaceholderCellIdentifier] autorelease];
UILabel *theDateLabel = [[UILabel alloc] initWithFrame:CGRectMake(140, 35,140, 20)];
theDateLabel.tag = DateLabelTag;
theDateLabel.backgroundColor = [UIColor clearColor];
theDateLabel.textColor = [UIColor lightGrayColor];
theDateLabel.font = [UIFont fontWithName:#"TrebuchetMS-Bold" size:15];
[cell.contentView addSubview:theDateLabel];
[theDateLabel release];
}
NSDate *theDate = [self dateForRowAtIndexPath:indexPath];
UILabel *theDateLabel = [cell.contentView viewWithTag:DateLabelTag];
theDateLabel.text = [dateFormatter stringFromDate:theDate];
return cell;
}

Answer 2

While Richard's solution will work, if your cells have any other subviews they'll get removed as well. Also, allocating and initializing your subviews every time you draw a cell isn't necessarily optimal.
The standard solution here is to create a subclass of UITableViewCell with a property #dateLabel (and so on for the other labels). Then, when you're initializing a cell, if it doesn't have a #dateLabel yet you can give it a new one, otherwise you only have to set its text.