Mixins.swift

protocol TableViewFooter:class {
    
    var footerActivityIndicator:UIActivityIndicatorView! {get set}
    var tableView:UITableView! {get set}
    func setupTableViewFooter()
}

extension TableViewFooter {
    
    func setupTableViewFooter() {
        
        let footerView = UIView(frame:CGRectMake(0, 0, 0, 44))
        
        // set up activity indicator
        footerActivityIndicator = UIActivityIndicatorView(frame:CGRectMake(0, 0, 44, 44))
        footerActivityIndicator.translatesAutoresizingMaskIntoConstraints = false
        footerActivityIndicator.hidesWhenStopped = true
        footerActivityIndicator.activityIndicatorViewStyle = .Gray
        
        footerView.addSubview(footerActivityIndicator)
        
        // Center Vertically
        let centerYConstraint = NSLayoutConstraint(item:self.footerActivityIndicator,attribute:.CenterY,relatedBy:.Equal,
                                                                                                        toItem:footerView,attribute:.CenterY,multiplier:1.0,constant:0.0)
        footerView.addConstraint(centerYConstraint)
        
        // Center Horizontally
        let centerXConstraint = NSLayoutConstraint(item:self.footerActivityIndicator,attribute:.CenterX,relatedBy:.Equal,
                                                                                                        toItem:footerView, attribute:.CenterX,multiplier:1.0,constant:0.0)
        footerView.addConstraint(centerXConstraint)
        
        tableView.tableFooterView = footerView
    }
}