Swift UICollectionView Cell being rendered twice

Question

I am writing a customer calendar as a challenge for me to practice UICollectionView. This issue has been puzzled me for few days. So the problem is when it reuses the cell, the load data source function has been called twice or three times, then it leads to:

Sometimes it's called three times and my calendar days become 100 110 etc.

Here is the delegate and datasource code:

extension CalendarViewController: UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return self.calendarPages.count
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath) as! CalendarCell
        cell.calendarPage = self.calendarPages[self.currentPageIndex]
        
        cell.contentView.addSubview(self.buildCalendarPage(index: indexPath.row, frame: cell.contentView.frame)) // this is where it add new month page to the calendar, and it's randomly called multiple times 
  
        print("cell called")
        return cell
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: collectionView.frame.width, height: collectionView.frame.height)
    }
}

Answer 1

I know what's going one there, so basically I made it too complicated, there is a calendar UICollectionView in another UICollectionView, (I just want to make it scrollable), so each time when the cell is reused, I forget to reload the UI

Solution, keep only one UICollectionView, each cell is a day, and create another UICollectionViewCell class to control the reusable cell, thanks for the Babar's help