Question

in my iPhone app I’m using an UITableView with custom cells. These cells contain different labels, mainly just representing text. But I’m using one of the labels as some sort of status indicator, by giving it different colors.
Since the scrolling became pretty slow I wanted to reuse the cells. Doing that gives me a good performance boost but the “status label” is beeing displayed wrong. The colors are not correct anymore for the different cells (All other labels are correct).

Anyone has experienced such problems and can give me a hint?

Edit:
The code for the custom tablecell

- (void)setIncident:(Incident *)_incident{
[self setSelectionStyle:UITableViewCellEditingStyleNone];
incident = _incident;

streamNameLbl.text = incident.streamName;
jobNameLbl.text = incident.jobName;
workInProgressByLbl.text = incident.workInProgressBy;
NSDateFormatter *tempFormatter = [[NSDateFormatter alloc] init];
[tempFormatter setDateFormat:@"hh:mm"];
errorTimeLbl.text = [NSString stringWithFormat:@"%@", [tempFormatter stringFromDate:incident.errorTime]];

[tempFormatter setDateFormat:@"dd. MMM"];
plandateLbl.text = [NSString stringWithFormat:@"%@", [tempFormatter stringFromDate:incident.planDate]];

returnCodeLbl.text = [@"RC: " stringByAppendingString: incident.returnCode];
runNumberLbl.text = [@"Run: " stringByAppendingString: incident.runNumber];
severityLbl.text = incident.severity;
restartStatusLblValue.text = incident.restartStatus;

    NSString * color = incident.severityColor;
    NSString * colorR = [color substringWithRange:NSMakeRange(1, 2)];
    NSString * colorG = [color substringWithRange:NSMakeRange(3, 2)];
    NSString * colorB = [color substringWithRange:NSMakeRange(5, 2)];

    unsigned intColorR = 0;
    unsigned intColorG = 0;
    unsigned intColorB = 0;

    NSScanner *scanner = [NSScanner scannerWithString:colorR];
    [scanner scanHexInt:&intColorR];
    scanner = [NSScanner scannerWithString:colorG];
    [scanner scanHexInt:&intColorG];
    scanner = [NSScanner scannerWithString:colorB];
    [scanner scanHexInt:&intColorB];

    incidentStatusLbl.backgroundColor = [UIColor clearColor];

    CAGradientLayer *gradient = [CAGradientLayer layer];
    gradient.frame = incidentStatusLbl.bounds;
    gradient.startPoint = CGPointMake(0, 0.5);
    gradient.endPoint = CGPointMake(1, 0.5);
    UIColor * startColor = [UIColor colorWithRed:1 green:1 blue:1 alpha:1];
    UIColor * endColor = [UIColor colorWithRed:intColorR/255.0 green:intColorG/255.0 blue:intColorB/255.0 alpha:1];
    gradient.colors = [NSArray arrayWithObjects:(id)[startColor CGColor], (id)[endColor CGColor], nil];

    [incidentStatusLbl.layer insertSublayer:gradient atIndex:0];
}

cellForRowAtIndexPath in the UITableView

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

incidentCell = (IncidentCell *)[tableView dequeueReusableCellWithIdentifier:@"IncidentCell"];
if (incidentCell == nil) {
    NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"IncidentCell" owner:self options:nil];
    incidentCell = [nib objectAtIndex:0];
     NSLog(@"Loading cell from xib file");
    }
else{
    NSLog(@"Reusing cell");    
     }

NSMutableArray *sectionDetails = ((NSMutableArray *)[incidentDic objectForKey:[self.sortedSections objectAtIndex:[indexPath section]]]);

Incident *incident = [sectionDetails objectAtIndex:[indexPath row]];

[incidentCell setIncident:incident];

return incidentCell;
}

Answer 1

As you are reusing cells, when a cell is asked in - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath it is not reloaded from your nib.
So if you set the label color to black in the nib for example, and you do in your code

if (some_condition) {
   cell.myLabel.textcolor= myStatusColor;
}

when a label has a myStatusColor color once, it will keep it when you’ll reuse it.

So you’ll have to do

if (some_condition) {
   cell.myLabel.textcolor= myStatusColor;
} else {
   cell.myLabel.textcolor= [UIColor black];
}

In fact your problem come from [incidentStatusLbl.layer insertSublayer:gradient atIndex:0];

If you use it once, you’ll have a subLayer, (let’s call it subLayer1). When you’ll reuse your cell, you’ll add another sublayer at index 0, BEHIND subLayer1. You may want to remove your old custom subLayer before.