什么时候创建属性实例?

问题描述

属性是否与应用它们的类的实例同时实例化?

Are attributes instantiated at the same time as instances of the class to which they are applied?

推荐答案

在调用 Type.GetCustomAttributes() 时会加载属性.如果只是实例化类，甚至获取类型，属性还没有加载.

Attributes are loaded when the Type.GetCustomAttributes() is called. If you just instantiate the class or even get the type, the attributes are not yet loaded.

看这个例子:

class Program
{
    static void Main()
    {
        Console.WriteLine("Calling AttributeLoadTest.TestStatic():");
        AttributeLoadTest.TestStatic();
        Console.WriteLine("Loading class");
        var x = new AttributeLoadTest();
        Console.WriteLine("Loading type..");
        var t = typeof (AttributeLoadTest);
        Console.WriteLine("Calling GetCustomAttributes()");
        var ats = t.GetCustomAttributes(false);
    }
}

[ConsoleTest]
class AttributeLoadTest
{
    public static void TestStatic()
    {

    }
}

[AttributeUsage(AttributeTargets.Class)]
class ConsoleTestAttribute : Attribute
{
    public ConsoleTestAttribute()
    {
        Console.WriteLine("ConsoleTestAttribute Constructor");
    }
}

打印出来:

调用 AttributeLoadTest.TestStatic():

Calling AttributeLoadTest.TestStatic():

加载类

加载类型..

调用 GetCustomAttributes()

Calling GetCustomAttributes()

ConsoleTestAttribute 构造函数

ConsoleTestAttribute Constructor

所以调用静态方法，实例化类，获取类型，并没有实例化属性.调用 GetCustomAttributes() 可以.

So calling a static method, instantiating the class, getting the type, does not instantiate the attribute. Calling GetCustomAttributes() does.

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