例如存在下列代码：
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namespace ExtensionMethods{ public static class MyExtensions { public static int zzyhost(this String str) { return 0; } } } |
那么在其他类下只需要 using ExtensionMethods;，所有 string 类型的对象就都拥有了 zzyhost() 这个方法，而无需你重写一个 string 类，比如：
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string s = "Hello zzyhost";int i = s.zzyhost(); |
像题主这段代码就是使得 Bitmap 这个类型多了一个 function() 方法。
C#动态调用泛型类、泛型方法
在制作一个批量序列化工具时遇到了如下问题，在此记录一下，仅供参考。
主程序加载另一个程序集，将其中的所有类取出，然后对这些类分别调用泛型类或泛型方法。控制台程序解决方案如下：
- Main工程：提供Worker类进行数据操作，XMLTool<T>泛型类将数据集序列化为.xml文档，RootCollection<T>类封装数据集
- Worker类
提供成员方法void DoWork<T>()、List<T> GetList<T>()、静态成员方法StaticDoWork<T>()，代码如下：
1 public class Worker
2 {
3 public Worker()
4 {
5 }
6
7 public void DoWork<T>()
8 {
9 Type t = typeof(T);
10 Console.WriteLine("Get Class: {0}", t.Name);
11 PropertyInfo[] properties = t.GetProperties();
12 foreach (PropertyInfo property in properties)
13 {
14 Console.WriteLine(" property.Name: " + property.Name + " property.MemberType: " + property.PropertyType);
15 }
16 }
17
18 public static void StaticDoWork<T>()
19 {
20 Type t = typeof(T);
21 Console.WriteLine("Get Class: {0}", t.Name);
22 PropertyInfo[] properties = t.GetProperties();
23 foreach (PropertyInfo property in properties)
24 {
25 Console.WriteLine(" property.Name: " + property.Name + " property.MemberType: " + property.PropertyType);
26 }
27 }
28
29 public List<T> GetList<T>()
30 {
31 Console.WriteLine("Generate List for [{0}]", typeof(T).Name);
32 return new List<T>()
33 {
34 Activator.CreateInstance<T>(),
35 Activator.CreateInstance<T>()
36 };
37 }
38 } - XMLTool<T>类
1publicclass XMLTool<T>
2 {
3publicstaticvoid XmlSerialize_Save(List<T> needSerializedList, string xmlDirPath, string xmlFileName)
4 {
5 RootCollection<T> collection = new RootCollection<T>();
6 collection.ItemList = needSerializedList;
7if (!Directory.Exists(xmlDirPath))
8 Directory.CreateDirectory(xmlDirPath);
9using (System.IO.FileStream stream = new System.IO.FileStream(xmlFileName, System.IO.FileMode.Create))
10 {
11 System.Xml.Serialization.XmlSerializer serializer = new System.Xml.Serialization.XmlSerializer(collection.GetType());
12 serializer.Serialize(stream, collection);
13 }
14 }
15 } - RootCollection<T>类：
1 [Serializable]
2 public class RootCollection<T>
3 {
4 public RootCollection()
5 {
6 itemList = new List<T>();
7 }
8
9 private List<T> itemList;
10
11 public List<T> ItemList
12 {
13 get { return itemList; }
14 set { itemList = value; }
15 }
16 } - MockClassLib工程：提供BaseEntity、Apple、Cat和Person类
- BaseEntity类：抽象类，负责初始化类成员
1 public abstract class BaseEntity
2 {
3 public BaseEntity()
4 {
5 InitiaWithNull();
6 }
7
8 private void InitiaWithNull()
9 {
10 Type type = this.GetType();
11 PropertyInfo[] properties = type.GetProperties();
12 string[] PropNames = new string[properties.Length];
13 Dictionary<string, PropertyInfo> PropNameToInfo = new Dictionary<string, PropertyInfo>();
14 for (int i = 0; i < properties.Length; i++)
15 {
16 PropNames[i] = properties[i].Name;
17 PropNameToInfo.Add(PropNames[i], properties[i]);
18 }
19
20 foreach (string propname in PropNames)
21 {
22 string proptype = PropNameToInfo[propname].PropertyType.Name;
23
24 object value = null;
25 if (NullValue.Keys.Contains(proptype))
26 value = NullValue[proptype];
27
28 type.GetProperty(propname).SetValue(this, value, null);
29 }
30 }
31
32 private static readonly Dictionary<string, object> NullValue = new Dictionary<string, object>()
33 {
34 { "String", String.Empty },
35 { "DateTime", DateTime.MinValue},
36 { "Decimal", Decimal.MinValue}
37 };
38 } - Apple、Cat和Person类：测试类，继承于BaseEntity
1 public class Apple : BaseEntity
2 {
3 public string Color { get; set; }
4 }
5
6 public class Cat : BaseEntity
7 {
8 public string Type { get; set; }
9 }
10
11 public class Person : BaseEntity
12 {
13 public int ID { get; set; }
14 public string Name { get; set; }
15 }
Main工程的Program的Main方法中，一般情况下，调用Worker的泛型方法来处理测试类的话，可以写为：
Worker worker = new Worker();
worker.DoWork<Apple>();
worker.DoWork<Cat>();
worker.DoWork<Person>();
但是，如果MockClassLib中需要处理的类型非常多时，这样显示调用必然是不灵活的，应当怎样向泛型方法DoWork<T>()的尖括号中动态传入类型呢？
考虑代码：
//Load assembly
Assembly mockAssembly = Assembly.LoadFrom("MockClassLibrary.dll");
Type[] typeArray = mockAssembly.GetTypes();
//Create instance of Worker
Worker worker = new Worker();
foreach(Type curType in typeArray)
{
worker.DoWork<curType>(); //Error
}
可以看到，Type类型的实例是无法直接传入泛型方法的尖括号中的，T要求显式指明类型名。
下面通过反射方式来获取泛型方法，并创建特定类型的泛型方法。
- 对于非静态方法：public void DoWork<T>()
对于非静态方法，调用MethodInfo.Invoke(object, object[])时，第一个参数需要指明泛型方法的所有者（即这里创建的worker对象），第二个参数为泛
型方法的参数列表，DoWork<T>()没有输入参数，所以设为null
//Create an instance of Worker
Worker worker = new Worker();
//Get type of Worker
Type workerType = typeof(Worker);
//Get Generic Method
MethodInfo doWorkMethod = workerType.GetMethod("DoWork");
//Invoke DoWork<T> with different Type
foreach (Type curType in typeArray)
{
if (curType.IsClass && !curType.IsAbstract)//Filter BaseEntity
{
MethodInfo curMethod = doWorkMethod.MakeGenericMethod(curType);
curMethod.Invoke(worker, null);//Member method，use instance
}
}
- 对于静态方法：public static void StaticDoWork<T>()
不同于非静态方法，这里直接反射的类静态方法，所以Invoke()的第一个参数设为null
//Get type of Worker
Worker worker = new Worker();
//Get Generic Method
MethodInfo staticDoWorkMethod = workerType.GetMethod("StaticDoWork");
//Invoke StaticDoWork<T>
foreach (Type curType in typeArray)
{
if (curType.IsClass && !curType.IsAbstract)
{
MethodInfo curMethod = staticDoWorkMethod.MakeGenericMethod(curType);
curMethod.Invoke(null, null);//Static method
}
}
- 对于有返回值的非静态方法：public List<T> GetList()
如同动态调用DoWork<T>()方法一样，只是在处理返回值时，可以使用下面的方法
1 IList tempList = (IList)curMethod.Invoke(worker, null);
2 //Or
3 IEnumerable tempList = (IEnumerable)curMethod.Invoke(worker, null);
- 对于泛型类：XMLTool<T>
下面要使用泛型类XMLTool<T>的静态方法public static void XmlSerialize_Save(List<T> list, string dirPath, string fileName)方法。
首先应通过反射构造出指定类型的泛型类XMLTool<T>，再反射出其中的XmlSerialize_Save方法并使用。
1 //Use Generic Class
2 Type xmlToolType = typeof(XMLTool<>).MakeGenericType(curType);
3
4 //Get method
5 MethodInfo saveMethod = xmlToolType.GetMethod("XmlSerialize_Save");
6
7 //Invoke
8 saveMethod.Invoke
9 (
10 null, //Static method
11 new object[] { resultList, @"c:", @"c:Test_" + curType.Name + ".xml" }
12 );
Program-->Main()方法的全部代码：
1 namespace RetrieveUnknownClass
2 {
3 class Program
4 {
5 static void Main(string[] args)
6 {
7 //Load assembly
8 Assembly mockAssembly = Assembly.LoadFrom("MockClassLibrary.dll");
9 Type[] typeArray = mockAssembly.GetTypes();
10
11 //Create instance of Worker
12 Type workerType = typeof(Worker);
13 Worker worker = new Worker();
14
15 #region Member method
16
17 Console.WriteLine(">>>>>>>>>Use Generic Method：");
18 MethodInfo doWorkMethod = workerType.GetMethod("DoWork");
19
20 //Invoke DoWork<T>
21 foreach (Type curType in typeArray)
22 {
23 if (curType.IsClass && !curType.IsAbstract)
24 {
25 MethodInfo curMethod = doWorkMethod.MakeGenericMethod(curType);
26 curMethod.Invoke(worker, null);//Member method，use instance
27 }
28 }
29
30 #endregion
31
32 #region Static method
33
34 Console.WriteLine(" >>>>>>>>>Use Static Generic Method：");
35 MethodInfo staticDoWorkMethod = workerType.GetMethod("StaticDoWork");
36
37 //Invoke StaticDoWork<T>
38 foreach (Type curType in typeArray)
39 {
40 if (curType.IsClass && !curType.IsAbstract)
41 {
42 MethodInfo curMethod = staticDoWorkMethod.MakeGenericMethod(curType);
43 curMethod.Invoke(null, null);//Static method
44 }
45 }
46
47 #endregion
48
49 #region Get A List & Serialize It to Xml File With Generic
50
51 Console.WriteLine(" >>>>>>>>>Get List By Generic Method：");
52 MethodInfo getListMethod = workerType.GetMethod("GetList");
53
54 foreach (Type curType in typeArray)
55 {
56 if (curType.IsClass && !curType.IsAbstract)
57 {
58 MethodInfo curMethod = getListMethod.MakeGenericMethod(curType);
59 //Generate List
60 IList resultList = (IList)curMethod.Invoke(worker, null);
61 //Show List
62 ShowList(resultList);
63 //Use Generic Class
64 Type xmlToolType = typeof(XMLTool<>).MakeGenericType(curType);
65 MethodInfo saveMethod = xmlToolType.GetMethod("XmlSerialize_Save");
66
67 saveMethod.Invoke
68 (
69 null, //Static method
70 new object[] { resultList, @"c:", @"c:Test_" + curType.Name + ".xml" }
71 );
72 }
73 }
74
75 Console.WriteLine("Serialization Completed... ");
76 #endregion
77 }
78
79 public static void ShowList(IList list)
80 {
81 Console.WriteLine("Type of list: {0} Count of current list: {1} Type of item in list: {2} ",
82 list.GetType(),
83 list.Count,
84 list[0].GetType());
85 }
86 }
87 }