kotlin - 构造函数可见性仅限于文件

Question

我想创建一种更简单的方法来处理 SharedPreferences。我想这样调用它

获取偏好:

val email = SharedPrefs.userdata.email
val wifiOnly = SharedPrefs.connections.wifiOnly

设置偏好:

SharedPrefs.userdata.email = "someone@example.com"
SharedPrefs.connections.wifiOnly = true

我可以这样做:

App.instance 在以下代码段中返回一个 Context 对象

object SharedPrefs {

    val userdata by lazy { UserPreferences() }
    val connections by lazy { ConnectionPreferences() }

    class UserPreferences {

        private val prefs: SharedPreferences = App.instance.getSharedPreferences("userdata", Context.MODE_PRIVATE)

        var email: String
            get() = prefs.getString("email", null)
            set(value) = prefs.edit().putString("email", value).apply()
    }

    class ConnectionPreferences {

        private val prefs: SharedPreferences = App.instance.getSharedPreferences("connections", Context.MODE_PRIVATE)

        var wifyOnly: Boolean
            get() = prefs.getBoolean("wifiOnly", false)
            set(value) = prefs.edit().putBoolean("wifyOnly", value).apply()
    }

}

问题是这仍然可以调用:SharedPrefs.UserPreferences()我能否使此构造函数仅对此文件或对象私有(private)？

Answer 1

可以把接口(interface)和实现类分开，让后者private给对象:

object SharedPrefs {
    val userdata: UserPreferences by lazy { UserPreferencesImpl() }

    interface UserPreferences {
        var email: String
    }

    private class UserPreferencesImpl : UserPreferences {
        private val prefs: SharedPreferences = 
            App.instance.getSharedPreferences("userdata", Context.MODE_PRIVATE)

        override var email: String
            get() = prefs.getString("email", null)
            set(value) = prefs.edit().putString("email", value).apply()
    }


    // ...
}

或者，如果您正在开发一个库或者您有一个模块化架构，您可以使用 internal visibility限制模块可见性的修饰符:

class UserPreferences internal constructor() { /* ... */ }