这节我们要讨论的是PostSharp的LocationInterceptionAspect，PostSharp官方把Property和Field成为Location。所以LocationInterceptionAspect就是为了实现Property和Field的拦截。在我们前面讨论了关于方法OnMethodBoundaryAspect的aspect，我们很容易想到，在c#中Property就是一个编译时分为Get和Set两个方法，对于property的aspect就类似于了我们的Method的aspect。而对于Field的aspect同样可以转换为对Property的aspect。
下面我们用反编译工具来证实一下我的说法.
LocationInterceptionAspect的使用方法和我们的OnMethodBoundaryAspect和类似，使用方式也一样，对于使用对不重要，鄙人觉得更重要的是我们的设计思想。
我暂时能想到的很好的LocationInterceptionAspect使用场景则是LazyLoad，对于3.5表达式的出现，我们到处都可以简单这个词，在c#类库中也加入了这个类。
[Serializable]
public class LazyLoadAttribute : LocationInterceptionAspect
{
public string MethodName
{
get;
private set;
}
public string PrivoderFullName
{
get;
private set;
}
public LazyLoadAttribute(
string MethodName,
string PrivoderFullName)
{
Green.Utility.Guard.ArgumentNotNullOrEmpty(MethodName,
" MethodName ");
Green.Utility.Guard.ArgumentNotNullOrEmpty(PrivoderFullName,
" PrivoderFullName ");
this.MethodName = MethodName;
this.PrivoderFullName = PrivoderFullName;
}
public override void OnGetValue(LocationInterceptionArgs args)
{
if (args.GetCurrentValue() ==
null)
{
Console.WriteLine(
" Loading.... ");
var value =
this.LoadProperty(args.Instance);
if (value !=
null)
{
args.Value = value;
args.ProceedSetValue();
}
}
args.ProceedGetValue();
}
private object LoadProperty(
object p)
{
var type = Type.GetType(
this.PrivoderFullName);
// 具体加载程序集需要自定义需求，这里仅为了测试简化。 if (type !=
null)
{
var method = type.GetMethod(
this.MethodName);
if (method !=
null)
{
object[] ps =
null;
if (p !=
null)
{
ps =
new object[] { p };
}
object entity =
null;
if (!method.IsStatic)
{
entity = System.Activator.CreateInstance(type);
}
return method.Invoke(entity, ps);
}
}
return null;
}
}
class Program
{
static void Main(
string[] args)
{
/* * demo4 */ Student stu =
new Student();
stu.ID =
10;
Console.WriteLine(stu.Name);
Console.WriteLine(stu.Name);
Console.WriteLine(Student.TestStaticProperty);
Console.WriteLine(Student.TestStaticProperty);
Console.Read();
}
public static string TextLazyLoadStaticMenthod(Student stu)
{
return " Student " + stu.ID;
}
public string TextLazyLoadInstacnceMenthod(Student stu)
{
return " Student " + stu.ID;
}
public string TextLazyLoadStaticPropertyMenthod()
{
return " 测试 ";
}
}
public class Student
{
// [LazyLoad("TextLazyLoadStaticMenthod", "PostSharpDemo.Program,PostSharpDemo")] [LazyLoad(
" TextLazyLoadInstacnceMenthod ",
" PostSharpDemo.Program,PostSharpDemo ")]
public string Name
{
get;
set; }
public string Sex
{
get;
set; }
[LazyLoad(
" TextLazyLoadStaticPropertyMenthod ",
" PostSharpDemo.Program,PostSharpDemo ")]
public static string TestStaticProperty
{
get;
set; }
public int ID
{
get;
set; }
}
