//從Xib中加載View
protocol NibLoadable {
}
extension NibLoadable where Self:UIView  {
    static func loadViewFromNib() -> Self {
        return Bundle.main.loadNibNamed("\(self)", owner: nil, options: nil)?.first as! Self
    }
}

//注冊UITableViewCell 
protocol RegisterCellOrNib {
}
extension RegisterCellOrNib {
    static var identifier:String {
        return "\(self)"
    }
    static var nib:UINib? {
        return UINib(nibName: "\(self)", bundle: nil)
    }
}

extension UITableView {

    func registerCell<T:UITableViewCell>(cell:T.Type) where T:RegisterCellOrNib {
        if let nib = T.nib { register(nib, forCellReuseIdentifier: T.identifier) }
        else { register(cell, forCellReuseIdentifier: T.identifier) }
    }
    /// 從緩存池池出隊已經(jīng)存在的 cell
    func dequeueReusableCell<T: UITableViewCell>(indexPath: IndexPath) -> T where T: RegisterCellOrNib {
        return dequeueReusableCell(withIdentifier: T.identifier, for: indexPath) as! T
    }
    func reloadRow(at indexPath:IndexPath, with animation: UITableView.RowAnimation) {
        reloadRows(at: [indexPath], with: animation)
    }
}

extension UICollectionView {
    /// 注冊 cell 的方法
    func registerCell<T: UICollectionViewCell>(cell: T.Type) where T: RegisterCellOrNib {
        if let nib = T.nib { register(nib, forCellWithReuseIdentifier: T.identifier) }
        else { register(cell, forCellWithReuseIdentifier: T.identifier) }
    }
    
    /// 從緩存池池出隊已經(jīng)存在的 cell
    func dequeueReusableCell<T: UICollectionViewCell>(indexPath: IndexPath) -> T where T: RegisterCellOrNib {
        return dequeueReusableCell(withReuseIdentifier: T.identifier, for: indexPath) as! T
    }
    
    /// 注冊頭部
    func registerSupplementaryHeaderView<T: UICollectionReusableView>(reusableView: T.Type) where T: RegisterCellOrNib {
        // T 遵守了 RegisterCellOrNib 協(xié)議，所以通過 T 就能取出 identifier 這個屬性
        if let nib = T.nib {
            register(nib, forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: T.identifier)
        } else {
            register(reusableView, forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: T.identifier)
        }
    }
    
    /// 獲取可重用的頭部
    func dequeueReusableSupplementaryHeaderView<T: UICollectionReusableView>(indexPath: IndexPath) -> T where T: RegisterCellOrNib {
        return dequeueReusableSupplementaryView(ofKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: T.identifier, for: indexPath) as! T
    }
}