构造函数何时运行？尝试一个示例：

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("Creating MyClass instance");
        MyClass mc = new MyClass();
        Console.WriteLine("Setting value in MyClass instance");
        mc.Value = 1;
        Console.WriteLine("Getting attributes for MyClass type");
        object[] attributes = typeof(MyClass).GetCustomAttributes(true);
    }

}

[AttributeUsage(AttributeTargets.All)]
public class MyAttribute : Attribute
{
    public MyAttribute()
    {
        Console.WriteLine("Running constructor");
    }
}

[MyAttribute]
class MyClass
{
    public int Value { get; set; }
}

输出是什么？

Creating MyClass instance
Setting value in MyClass instance
Getting attributes for MyClass type
Running constructor

因此，当我们开始检查属性时，将运行属性构造函数。请注意，属性是从类型而不是类型的实例中获取的。