[UI-Kit] CollectionView Cell Selection / Deselection

 

 

 

 

# shouldSelecItemAt

    func collectionView(_ collectionView: UICollectionView, shouldSelectItemAt indexPath: IndexPath) -> Bool {
        guard let cell = collectionView.cellForItem(at: indexPath) as? SelectPlanetCollectionViewCell else {
            return true
        }
        
        if cell.isSelected {
            // TODO: 탐색 모드로 변환
            cell.planetNameLabel.textColor = .white
            cell.backgroundView = nil
            self.navigationController?.topViewController?.title = "빠르게 천체 찾기"
            collectionView.deselectItem(at: indexPath, animated: true)
            return false
        } else {
            return true
        }
    }

 

 

 

# didSelectItemAt

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        guard let cell = collectionView.cellForItem(at: indexPath) as? SelectPlanetCollectionViewCell else { return }
           
        if cell.isSelected {
            cell.planetNameLabel.textColor = .black
            cell.backgroundView = cell.planetBackgroundView
            
            // navigation title 변경
            self.navigationController?.topViewController?.title = "\(cell.planetNameLabel.text ?? "천체") 탐색 중"
            self.navigationController?.navigationBar.titleTextAttributes = [ NSAttributedString.Key.foregroundColor: UIColor.white]
            self.navigationController?.navigationBar.backgroundColor = .black
        }
    }

 

 

 

# didDeselectItemAt

    func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
        if let cell = collectionView.cellForItem(at: indexPath) as? SelectPlanetCollectionViewCell {
            cell.planetNameLabel.textColor = .white
            cell.backgroundView = nil
        }
    }

 

 

 

 

 

 

shouldSelectItemAt

true -> didSelectItemAt을 호출

동일한 cell을 재선택했을 때, 취소 동작 (false return)

true를 return하면 선택을 허용 / false를 return하면 선택을 허용하지 않음

 

 

didDeselectItemAt

Programmatically 호출을 안한다.

다른 cell을 선택했을 때, 취소 동작

This method doesn’t cause any selection-related delegate methods to be called.

-> 이게 계속 나왔던 programmatically 선택 . 선택 취소를 의미하는 것 같은데?

- programmatically에서는 shouldSelectItemAt, didSelectItemAt, didDeselectItemAt 이런 함수들 호출 안한다는 내용

 

 

 

 

 

 

# 공식 문서 공부

1. didSelectItemAt

The collection view calls this method when the user successfully selects an item in the collection view.

It does not call this method when you programmatically set the selection.

https://developer.apple.com/documentation/uikit/uicollectionviewdelegate/1618032-collectionview

 

 

 

 

2. didDeselectItemAt

The collection view calls this method when the user successfully deselects an item in the collection view.

It does not call this method when you programmatically deselect items.

deselect : 다른 cell을 선택하게 되면, 기존에 선택된 cell이 deselect 되는 것 (즉 선택이라는 행위의 끝을 의미함)

우리는 다른 cell을 택할 때 / 선택된 cell을 다시 택할 때 (두가지 모두 '선택'에 집중된 동작)

Deselct 에서 구현할 것이 아니라, select의 순서에 주의해야 했다. (bool List -> Should Select item at)

https://developer.apple.com/documentation/uikit/uicollectionviewdelegate/1618035-collectionview

 

 

 

3. shouldSelectItemAt

Asks the delegate if the specified item should be selected. 

The collection view calls this method when the user tries to select an item in the collection view.
It does not call this method when you programmatically set the selection. 
true if the item should be selected or false if it should not. 
아이템이 선택되어야 한다면 -> true 반환 / 아이템이 선택되어야 하지 않는다면 -> false 반환

언제 아이템이 선택되면 안된다는건데? -> 이미 선택된 아이템에 대하여

넌 이미 선택 동작이 이루어진 이후니까, 재선택 관련 코드들과 함께, return false
If you do not implement this method, the default return value is true.

https://developer.apple.com/documentation/uikit/uicollectionviewdelegate/1618095-collectionview

 

 

 

 

4. deselectItem

Deselects the item at the specified index.

If the allowsSelection property is false, calling this method has no effect. 
This method doesn’t cause any selection-related delegate methods to be called.
이게 의미하는 바 -> deselectItem == Programmatically deselect items 의미!  
https://developer.apple.com/documentation/uikit/uicollectionview/1618040-deselectitem

 

 

 

5. selectItem

Selects the item at the specified index path and optionally scrolls it into view.

func selectItem(
    at indexPath: IndexPath?,
    animated: Bool,
    scrollPosition: UICollectionView.ScrollPosition
)

 

 

scrollPosition : An option that specifies where the item should be positioned when scrolling finishes.
If the allowsSelection property is false, calling this method has no effect.
If there’s an existing selection with a different index path and the allowsMultipleSelection property is false, calling this method replaces the previous selection.
This method doesn’t cause any selection-related delegate methods to be called.
https://developer.apple.com/documentation/uikit/uicollectionview/1618057-selectitem