Question

以下代码来自关于Kotlin的示例项目，我可以使用代码1来获取共享首选项的值，但我可以设置共享首选项的值吗？

我无法在示例项目中找到这些代码，您能告诉我我该怎么做吗？谢谢！

代码1

class SettingsActivity : AppCompatActivity() {

    companion object {
        val ZIP_CODE = "zipCode"
        val DEFAULT_ZIP = 94043L
    }

    var zipCode: Long by DelegatesExt.preference(this, ZIP_CODE, DEFAULT_ZIP)
}

代码2

object DelegatesExt {
    fun <T> notNullSingleValue() = NotNullSingleValueVar<T>()
    fun <T> preference(context: Context, name: String, default: T) = Preference(context, name, default)
}

class NotNullSingleValueVar<T> {

    private var value: T? = null

    operator fun getValue(thisRef: Any?, property: KProperty<*>): T {
        return value ?: throw IllegalStateException("${property.name} not initialized")
    }

    operator fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
        this.value = if (this.value == null) value
        else throw IllegalStateException("${property.name} already initialized")
    }
}

class Preference<T>(val context: Context, val name: String, val default: T) {

    val prefs: SharedPreferences by lazy { context.getSharedPreferences("default", Context.MODE_PRIVATE) }

    operator fun getValue(thisRef: Any?, property: KProperty<*>): T {
        return findPreference(name, default)
    }

    operator fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
        putPreference(name, value)
    }

    @Suppress("UNCHECKED_CAST")
    private fun findPreference(name: String, default: T): T = with(prefs) {
        val res: Any = when (default) {
            is Long -> getLong(name, default)
            is String -> getString(name, default)
            is Int -> getInt(name, default)
            is Boolean -> getBoolean(name, default)
            is Float -> getFloat(name, default)
            else -> throw IllegalArgumentException("This type can be saved into Preferences")
        }

        res as T
    }

    private fun putPreference(name: String, value: T) = with(prefs.edit()) {
        when (value) {
            is Long -> putLong(name, value)
            is String -> putString(name, value)
            is Int -> putInt(name, value)
            is Boolean -> putBoolean(name, value)
            is Float -> putFloat(name, value)
            else -> throw IllegalArgumentException("This type can't be saved into Preferences")
        }.apply()
    }
}

以及

如果函数putPreference是公共的，我可以使用下面的代码设置共享首选项的值，但它很难看

class SettingsActivity : AppCompatActivity() {

    companion object {
        val ZIP_CODE = "zipCode"
        val DEFAULT_ZIP = 94043L
    }

   DelegatesExt.Preference(this, ZIP_CODE, DEFAULT_ZIP).putPreference( ZIP_CODE,"99999L");
}

Answer 1

这就是operator fun setValue的用途：你只需写

activity.zipCode = 1L

（其中activity是SettingsActivity）或

zipCode = 1L

（在SettingsActivity内或扩展它的类），它会调用setValue(activity, activity::zipCode, 1L)来调用putPreference("zipCode", 1L)。有关详情，请参阅https://kotlinlang.org/docs/reference/delegated-properties.html。

如何在Kotlin中设置值偏好？

1 个答案: