Swift 類方法 和OC類似，就是通過類本身調用方法，在方法（func）關鍵字前面用static修飾，如果父類允許子類重載方法，就用關鍵字class修飾

import UIKit
import Foundation
class MsgToolBox: NSObject {
    static public func showAlert(title: String, content: String) -> () {
        //保證在主線程上執行
        if Thread.isMainThread == true {
            let alertView = UIAlertView.init(title: title, message: content, delegate: self, cancelButtonTitle: "已閱")
            alertView.show()
        } else {
            DispatchQueue.main.async {
                let alertView = UIAlertView.init(title: title, message: content, delegate: self, cancelButtonTitle: "已閱")
                alertView.show()
            }
        }
    }
}

//調用
MsgToolBox.showAlert(title: "溫馨提示", content: "請輸入標簽！")