在没有实例的情况下访问Kotlin委托类型

Question

class Example
{
    var nonDelegatedProperty = "I don't care about this property"
    var delegatedProperty1 by lazy { "I don't care about this too" }
    var delegatedProperty2 by CustomDelegate("I care about this one")
}

Answer 1

如果我有Kclass ,但不是Example的实例,我如何获得委托给CustomDelegate的所有属性？

根据你的需要，你可以用两种方法来做。

首先，必须在build.gradle文件中包含Kotlin-Reflection依赖项：

compile "org.jetbrains.kotlin:kotlin-reflect:1.1.51"

// Loop on the properties of this class.
Example::class.declaredMemberProperties.filter { property ->
    // If the type of field is CustomDelegate or the delegate is an instance of CustomDelegate,
    // it will return true.
    CustomDelegate::class.java == property.javaField?.type
}

class Example {
    var nonDelegatedProperty = "I don't care about this property"
    val delegatedProperty1 by lazy { "I don't care about this too" }
    val delegatedProperty2 by CustomDelegate("I care about this one")
    val customDelegate = CustomDelegate("jdo")
}

您将获得DelegatedProperty2和CustomDelegate。如果您只想获得delegatedproperty2，我找到了一个可怕的解决方案，如果需要管理这种情况，您可以使用它。

第二

如果检查KPropertyImpl的源代码，就可以看到委派是如何实现的。所以，你可以这样做：

// Loop on the properties of this class.
Example::class.declaredMemberProperties.filter { property ->
    // You must check in all superclasses till you find the right method.
    property::class.allSuperclasses.find {
        val computeField = try {
            // Find the protected method "computeDelegateField".
            it.declaredFunctions.find { it.name == "computeDelegateField" } ?: return@find false
        } catch (t: Throwable) {
            // Catch KotlinReflectionInternalError.
            return@find false
        }

        // Get the delegate or null if the delegate is not present.
        val delegateField = computeField.call(property) as? Field
        // If the delegate was null or the type is different from CustomDelegate, it will return false.
        CustomDelegate::class.java == delegateField?.type
    } != null
}