iOS 解決鍵盤遮擋輸入框問題，輸入框隨鍵盤彈起上移，切換輸入法時動態調整 (Swift)

最近在專案中需要解決蘋果系統輸入法遮擋輸入框的問題，預期結果為：

1. 若鍵盤彈出后會遮擋輸入框，則輸入框隨鍵盤彈起上移，輸入法切換時輸入框始終保持在距鍵盤上方 4pt 處;
2. 若鍵盤彈出后不會遮擋輸入框，但切換輸入法后會遮擋輸入框，則輸入框需要在切換后上移，隨后輸入法切換時輸入框始終保持在鍵盤上方 4pt 處，

效果示意：/待補充/

一. 背景

開發環境：iOS14.2 + Xcode v12.2 + Swift5
設備：iPhoneSE（其他機型測驗有效）
頁面采用自動布局

頁面結構：/待補充/

二. 實作方式

在viewWillAppear中添加鍵盤彈出、收起、frame變化的通知

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    // 鍵盤彈出監聽，解決鍵盤擋住輸入框的問題
    NotificationCenter.default.addObserver(self,
                                           selector: #selector(keyboardWillAppear),
                                           name: UIResponder.keyboardWillShowNotification,
                                           object: nil)
    NotificationCenter.default.addObserver(self,
                                           selector: #selector(keyboardHasAppear),
                                           name: UIResponder.keyboardDidShowNotification,
                                           object: nil)
    NotificationCenter.default.addObserver(self,
                                           selector: #selector(keyboardWillDisappear),
                                           name: UIResponder.keyboardWillHideNotification,
                                           object: nil)
    NotificationCenter.default.addObserver(self,
                                           selector: #selector(keyboardFrameDidChange),
                                           name: UIResponder.keyboardDidChangeFrameNotification,
                                           object: nil)
}

（相關鏈接：iOS鍵盤通知）

添加成員變數：

private var keyboardFlag: Int = 0 // 鍵盤彈起情況，收起=0
private var deltaHeight: CGFloat = 0 // 鍵盤與輸入框間距
private var nameFieldBottomHeight: CGFloat = 0 // 輸入框底部到頁面底部距離
private var transformDistance: CGFloat = 0 // 頁面移動距離

實作 keyboardWillAppear：

@objc
func keyboardWillAppear(noti: Notification) {
    // 獲得軟鍵盤的高
    let keyboardSize = (noti.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue
    let keyboardHeight = keyboardSize?.height

    // 計算輸入框和軟鍵盤的高度差
    let rect = self.nickNameEditView.containerView
        .convert(self.nickNameEditView.containerView.bounds,
                 to: self.view) // 將rect由rect所在視圖轉換到目標視圖view中，回傳在目標視圖view中的rect

    self.nameFieldBottomHeight = self.view.bounds.height - (rect.origin.y + rect.size.height)
    self.deltaHeight = (keyboardHeight ?? 0) - self.nameFieldBottomHeight

    if self.keyboardFlag == 0, self.deltaHeight > 0 { // 鍵盤原來是收起的，且遮擋輸入框
        self.pageContainerView.transform = CGAffineTransform(a: 1, b: 0, c: 0, d: 1,
                                                             tx: 0, ty: -self.deltaHeight - 4)
        self.transformDistance = -self.deltaHeight - 4
        /* -4：為了使鍵盤距離輸入框底部距離為4pt，該值可改 */
    }
}

實作keyboardHasAppear：

@objc
func keyboardHasAppear() {
    self.keyboardFlag = 1 // 鍵盤已彈出
}

實作keyboardWillDisappear：

@objc
func keyboardWillDisappear() {
    if self.keyboardFlag == 0 {
		// 軟鍵盤收起的時候恢復原始偏移
		self.pageContainerView.transform = CGAffineTransform.identity
		self.transformDistance = 0
	}
}

實作 keyboardFrameDidChange，解決切換輸入法動態調整：

@objc
func keyboardFrameDidChange(noti: Notification) {
    // 獲得軟鍵盤的高
    let keyboardSize = (noti.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue
    let keyboardHeight = keyboardSize?.height

    // 計算輸入框和軟鍵盤的高度差
    self.deltaHeight = (keyboardHeight ?? 0) - (self.nameFieldBottomHeight + self.transformDistance)

    // 鍵盤在彈出的情況下如果frame有變化就改變輸入框位置
    if self.keyboardFlag == 1 {
        // 如果頁面之前沒有上移，鍵盤遮擋輸入框，頁面上移; 頁面之前有上移，輸入框下降到鍵盤上方4pt處
        if (self.transformDistance == 0 && self.deltaHeight > 0) || (self.transformDistance != 0) {
            self.pageContainerView.transform = CGAffineTransform(a: 1, b: 0, c: 0, d: 1,
                                                                 tx: 0, ty: -self.deltaHeight - 4)
            self.transformDistance = -self.deltaHeight - 4
        }
    }
}

點擊空白區域收取鍵盤：

// 收起鍵盤
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    if self.nickNameEditView.nameTextField.isFirstResponder {
        self.keyboardFlag = 0
        self.nickNameEditView.nameTextField.resignFirstResponder()
    }
}

在 viewWillDisappear 中移除通知：

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    
    NotificationCenter.default.removeObserver(self, name: UIResponder.keyboardWillShowNotification, object: nil)
    NotificationCenter.default.removeObserver(self, name: UIResponder.keyboardDidShowNotification, object: nil)
    NotificationCenter.default.removeObserver(self, name: UIResponder.keyboardWillHideNotification, object: nil)
    NotificationCenter.default.removeObserver(self, name: UIResponder.keyboardDidChangeFrameNotification, object: nil)
}