Strange bug on dequeuing collectionviewcell

Question

I have a calendarView made up of collectionView. It is a custom calendarView derived using mathematical calculations. The seventh row marks Saturday and it's holiday so the font color is red for the all the labels of seventh column. However, when I swipe or navigate to other days, the red color labels are scattered in random order which is untraceable. A screenshot is herewith:

How did this occur? In my dequeueReusableCell method I have cell configured for holiday as:

cell.isHoliday = (indexPath.row + 1) % 7 == 0 ? true : false

And this is the logic for holiday in my custom collectionViewCell.

@IBOutlet var dateLabel: UILabel!
@IBOutlet var englishDateLabel: UILabel!
@IBOutlet var tithiLabel: UILabel!

var isToday: Bool = false {
    didSet {
        self.contentView.backgroundColor = isToday ? Colors.Palette.LightGreen : UIColor.white
    }
}

var isHoliday: Bool = false {
    didSet {
        if isHoliday {
            tithiLabel.textColor = Colors.Palette.DarkRed
            dateLabel.textColor = Colors.Palette.DarkRed
            englishDateLabel.textColor = Colors.Palette.DarkRed
        }
        else {
            dateLabel.textColor = UIColor.black
            englishDateLabel.textColor = UIColor.black
        }
    }
}

The number of red labels on top of each collectionview cells goes on increasing as I swipe to next month. Why is this happening and how can I stop this from happening?

Happens because cells are reused after dequeuing, use `prepareForReuese` to clear out old values. — saurabh, May 16 '17 at 10:58

score 1 · Accepted Answer · answered May 16 '17 at 10:59

You are missing else part:

var isHoliday: Bool = false {
    didSet {
        if isHoliday {
            tithiLabel.textColor = Colors.Palette.DarkRed
            dateLabel.textColor = Colors.Palette.DarkRed
            englishDateLabel.textColor = Colors.Palette.DarkRed
        }
        else {
            tithiLabel.textColor = UIColor.black
            dateLabel.textColor = UIColor.black
            englishDateLabel.textColor = UIColor.black
        }
    }
}

score 1 · Answer 2 · answered May 16 '17 at 11:00

1

This may be because the cell is being reused and you are not implemented any logic in prepareForReuse method of your custom cell class. In this method try setting text colour properties to nil.

answered May 16 '17 at 11:00

jegadeesh

875
9
22

saurabh · Answer 3 · 2017-05-16T11:07:32.200

The right way to deal with old data showing up in reused cells is to override prepeareForReuse in your custom cell

open override func prepareForReuse() {
    super.prepareForReuse()

     tithiLabel.textColor = UIColor.black
     dateLabel.textColor = UIColor.black
     englishDateLabel.textColor = UIColor.black
}

Clear out old values (by assigning them to nil) or set defaults to all values that might not necessarily be set after the cell is reused. This way, even if the new value(s) are not explicitly set to the cell, you are sure that old values are not being retained.

Strange bug on dequeuing collectionviewcell

3 Answers3