单例与sharedpreference的应用

单例配合sharedpreference实现存储密码：

//    私有化构造方法
class sharePrefre private constructor(){
    private val FILE_NAME = "passward"
    private val KEY = "passwardKey"
//    伴生对象
    companion object{
        private var instant: sharePrefre? = null
        private var mContext:Context? = null

        fun  getInstance(context: Context):sharePrefre{
            mContext = context
            if (instant == null){
                instant = sharePrefre()
            }
            return instant!!
        }
    }
//    保存密码
    fun savePassward(passward: String){
        mContext?.getSharedPreferences(FILE_NAME,Context.MODE_PRIVATE).also {
            it?.edit().also {
                it?.putString(KEY,passward)
                it?.apply()
            }
        }
    }
//    获取密码
    fun getPassward():String?{
        mContext?.getSharedPreferences(FILE_NAME,Context.MODE_PRIVATE).also {
            return it?.getString(KEY,null)
         }
    }
}

调用：
rPassward = sharePrefre.getInstance(this).getPassward()
sharePrefre.getInstance(this).savePassward(firstParssward!!)