反射-动态加载和使用类型
1
反射提供语言编译器（如 Microsoft Visual Basic
2005
和 JScript）用于实现隐式后期绑定的基础结构。绑定是查找与唯一指定的类型相对应的声明（即实现）的过程。如果此过程是在运行时而不是在编译时发生，则称其为“后期绑定”。利用 Visual Basic
2005
，可以在代码中使用隐式后期绑定；Visual Basic 编译器会调用一个帮助器方法，该方法使用反射来获取对象类型。传递给帮助器方法的参数有助于在运行时调用正确的方法。这些参数包括：对其调用方法的实例（对象），被调用方法的名称（字符串），以及传递给被调用方法的参数（对象数组）。
2
3在下面的示例中，Visual Basic 编译器使用反射隐式地对其类型在编译时未知的对象调用方法。HelloWorld 类具有一个 PrintHello 方法，它输出与传递给 PrintHello 方法的某些文本串联的“Hello World”。在此示例中调用的 PrintHello 方法实际上是 Type..::.InvokeMember；Visual Basic 代码允许按照对象 (helloObj) 的类型在编译时已知（早期绑定）而不是在运行时已知（后期绑定）的方式来调用 PrintHello 方法。
4
5 复制代码
6Imports System
7Module Hello
8 Sub Main()
9
'
Sets up the variable.
10
Dim helloObj As Object
11
'
Creates the object.
12
helloObj
=
new
HelloWorld()
13
'
Invokes the print method as if it was early bound
14
'
even though it is really late bound.
15
helloObj.PrintHello(
"
Visual Basic Late Bound
"
)
16 End Sub
17End Module
18
19
20自定义绑定
21除了由编译器隐式地用来进行后期绑定之外，反射还可以在代码中显式地用来完成后期绑定。
22
23公共语言运行库支持多种编程语言，但这些语言的绑定规则各不相同。在早期绑定的情况下，代码生成器可以完全控制此绑定。但是，当通过反射进行后期绑定时，必须用自定义绑定来控制绑定。Binder 类提供了对成员选择和调用的自定义控制。
24
25利用自定义绑定，您可以在运行时加载程序集，获取有关该程序集中类型的信息，然后对该类型调用方法或访问该类型的字段或属性。如果您在编译时（例如当对象类型依赖于用户输入时）不知道对象的类型，就可以使用这种方法。
26
27下面的示例说明不提供参数类型转换的简单的自定义联编程序。Simple_Type.dll 的代码位于示例主体之前。确保生成 Simple_Type.dll，然后在生成时在项目中包括对它的引用。
28
29Visual Basic 复制代码
30
'
Code for building Simple_Type.dll.
31
Imports System
32
33Namespace Simple_Type
34 Public Class MySimpleClass
35 Public Overloads Sub MyMethod(ByVal str As String,
36 ByVal i As Integer)
37 Console.WriteLine(
"
MyMethod parameters: {0}, {1}
"
, str, i)
38 End Sub
'
MyMethod
39
40 Public Overloads Sub MyMethod(ByVal str As String,
41 ByVal i As Integer, ByVal j As Integer)
42 Console.WriteLine(
"
MyMethod parameters: {0}, {1}, {2}
"
, str,
43 i, j)
44 End Sub
'
MyMethod
45
End Class
'
MySimpleClass
46
End Namespace
'
Simple_Type
47
48Imports System
49Imports System.Reflection
50Imports System.Globalization
51Imports Simple_Type.Simple_Type
52
53Namespace Custom_Binder
54 Class MyMainClass
55 Shared Sub Main()
56
'
Get the type of MySimpleClass.
57
Dim myType As Type
=
GetType(MySimpleClass)
58
'
Get an instance of MySimpleClass.
59
Dim myInstance As New MySimpleClass()
60 Dim myCustomBinder As New MyCustomBinder()
61
'
Get the method information for the overload being sought.
62
Dim myMethod As MethodInfo
=
myType.GetMethod(
"
MyMethod
"
,
63 BindingFlags.Public Or BindingFlags.Instance,
64
myCustomBinder, New Type()
{GetType(String),
65
GetType(Integer)}
, Nothing)
66 Console.WriteLine(myMethod.ToString())
67
'
Invoke the overload.
68
myType.InvokeMember(
"
MyMethod
"
, BindingFlags.InvokeMethod,
69 myCustomBinder, myInstance,
70 New [Object]()
{"Testing
", CInt(32)}
)
71 End Sub
'
Main
72
End Class
'
MyMainClass
73
74
'
****************************************************
75
'
A simple custom binder that provides no
76
'
argument type conversion.
77
'
****************************************************
78
Class MyCustomBinder
79 Inherits Binder
80
81 Public Overrides Function BindToMethod(ByVal bindingAttr As
82 BindingFlags, ByVal match() As MethodBase, ByRef args() As
83 Object, ByVal modifiers() As ParameterModifier, ByVal
84 culture As CultureInfo, ByVal names() As String, ByRef
85 state As Object) As MethodBase
86 If match Is Nothing Then
87 Throw New ArgumentNullException(
"
match
"
)
88 End If
89
'
Arguments are not being reordered.
90
state
=
Nothing
91
'
Find a parameter match and return the first method with
92
'
parameters that match the request.
93
Dim mb As MethodBase
94 For Each mb In match
95 Dim parameters As ParameterInfo()
=
mb.GetParameters()
96 If ParametersMatch(parameters, args) Then
97 Return mb
98 End If
99 Next mb
100 Return Nothing
101 End Function
'
BindToMethod
102
103 Public Overrides Function BindToField(ByVal bindingAttr As
104 BindingFlags, ByVal match() As FieldInfo, ByVal value As
105 Object, ByVal culture As CultureInfo) As FieldInfo
106 If match Is Nothing Then
107 Throw New ArgumentNullException(
"
match
"
)
108 End If
109 Dim fi As FieldInfo
110 For Each fi In match
111 If fi.GetType() Is value.GetType() Then
112 Return fi
113 End If
114 Next fi
115 Return Nothing
116 End Function
'
BindToField
117
118 Public Overrides Function SelectMethod(ByVal bindingAttr As
119 BindingFlags, ByVal match() As MethodBase, ByVal types() As
120 Type, ByVal modifiers() As ParameterModifier) As
121 MethodBase
122 If match Is Nothing Then
123 Throw New ArgumentNullException(
"
match
"
)
124 End If
125
'
Find a parameter match and return the first method with
126
'
parameters that match the request.
127
Dim mb As MethodBase
128 For Each mb In match
129 Dim parameters As ParameterInfo()
=
mb.GetParameters()
130 If ParametersMatch(parameters, types) Then
131 Return mb
132 End If
133 Next mb
134 Return Nothing
135 End Function
'
SelectMethod
136
137 Public Overrides Function SelectProperty(ByVal bindingAttr As
138 BindingFlags, ByVal match() As PropertyInfo, ByVal returnType
139 As Type, ByVal indexes() As Type, ByVal modifiers() As
140 ParameterModifier) As PropertyInfo
141 If match Is Nothing Then
142 Throw New ArgumentNullException(
"
match
"
)
143 End If
144 Dim pi As PropertyInfo
145 For Each pi In match
146 If pi.GetType() Is returnType And
147 ParametersMatch(pi.GetIndexParameters(), indexes) Then
148 Return pi
149 End If
150 Next pi
151 Return Nothing
152 End Function
'
SelectProperty
153
154 Public Overrides Function ChangeType(ByVal value As Object,
155 ByVal myChangeType As Type, ByVal culture As CultureInfo)
156 As Object
157 Try
158 Dim newType As Object
159 newType
=
Convert.ChangeType(value, myChangeType)
160
161 Return newType
162
'
Throw an InvalidCastException if the conversion cannot
163
'
be done by the Convert.ChangeType method.
164
Catch
165 End Try
166 End Function
'
ChangeType
167
168 Public Overrides Sub ReorderArgumentArray(ByRef args() As Object,
169 ByVal state As Object)
170
'
No operation is needed here because BindToMethod does not
171
'
reorder the args array. The most common implementation
172
'
of this method is shown below.
173
174
'
((BinderState)state).args.CopyTo(args, 0);
175
End Sub
'
ReorderArgumentArray
176
177
'
Returns true only if the type of each object in a matches
178
'
the type of each corresponding object in b.
179
Private Overloads Function ParametersMatch(ByVal a() As
180 ParameterInfo, ByVal b() As Object) As Boolean
181 If a.Length
<>
b.Length Then
182 Return False
183 End If
184 Dim i As Integer
185 For i
=
0
To a.Length
-
1
186 If Not (a(i).ParameterType Is b(i).GetType()) Then
187 Return False
188 End If
189 Next i
190 Return True
191 End Function
'
ParametersMatch
192
193
'
Returns true only if the type of each object in a matches
194
'
the type of each corresponding entry in b.
195
Private Overloads Function ParametersMatch(ByVal a() As
196 ParameterInfo, ByVal b() As Type) As Boolean
197 If a.Length
<>
b.Length Then
198 Return False
199 End If
200 Dim i As Integer
201 For i
=
0
To a.Length
-
1
202 If Not (a(i).ParameterType Is b(i)) Then
203 Return False
204 End If
205 Next i
206 Return True
207 End Function
'
ParametersMatch
208
End Class
'
MyCustomBinder
209
End Namespace
'
Custom_Binder
210
211
212
213
214C# 复制代码
215
//
Code for building SimpleType.dll.
216
using
System;
217
218
namespace
Simple_Type
219
{
220
public class MySimpleClass
221
{
222 public void MyMethod(string str, int i)
223 {
224 Console.WriteLine("MyMethod parameters: {0}, {1}", str, i);
225
}
226
227 public void MyMethod(string str, int i, int j)
228 {
229 Console.WriteLine("MyMethod parameters: {0}, {1}, {2}",
230 str, i, j);
231 }
232 }
233}
234
235
236
using
System;
237
using
System.Reflection;
238
using
System.Globalization;
239
using
Simple_Type;
240
namespace
Custom_Binder
241
{
242 class MyMainClass
243 {
244 static void Main()
245 {
246 // Get the type of MySimpleClass.
247 Type myType = typeof(MySimpleClass);
248
249 // Get an instance of MySimpleClass.
250 MySimpleClass myInstance = new MySimpleClass();
251 MyCustomBinder myCustomBinder = new MyCustomBinder();
252
253 // Get the method information for the particular overload
254 // being sought.
255 MethodInfo myMethod = myType.GetMethod("MyMethod",
256 BindingFlags.Public | BindingFlags.Instance,
257 myCustomBinder, new Type[] {typeof(string),
258 typeof(int)}, null);
259 Console.WriteLine(myMethod.ToString());
260
261 // Invoke the overload.
262 myType.InvokeMember("MyMethod", BindingFlags.InvokeMethod,
263 myCustomBinder, myInstance,
264 new Object[] {"Testing", (int)32});
265 }
266 }
267
268 //****************************************************
269 // A simple custom binder that provides no
270 // argument type conversion.
271 //****************************************************
272 class MyCustomBinder : Binder
273 {
274 public override MethodBase BindToMethod(
275 BindingFlags bindingAttr,
276 MethodBase[] match,
277 ref object[] args,
278 ParameterModifier[] modifiers,
279 CultureInfo culture,
280 string[] names,
281 out object state)
282 {
283 if(match == null)
284 throw new ArgumentNullException("match");
285 // Arguments are not being reordered.
286 state = null;
287 // Find a parameter match and return the first method with
288 // parameters that match the request.
289 foreach(MethodBase mb in match)
290 {
291 ParameterInfo[] parameters = mb.GetParameters();
292
293 if(ParametersMatch(parameters, args))
294 return mb;
295 }
296 return null;
297 }
298
299 public override FieldInfo BindToField(BindingFlags bindingAttr,
300 FieldInfo[] match, object value, CultureInfo culture)
301 {
302 if(match == null)
303 throw new ArgumentNullException("match");
304 foreach(FieldInfo fi in match)
305 {
306 if(fi.GetType() == value.GetType())
307 return fi;
308 }
309 return null;
310 }
311
312 public override MethodBase SelectMethod(
313 BindingFlags bindingAttr,
314 MethodBase[] match,
315 Type[] types,
316 ParameterModifier[] modifiers)
317 {
318 if(match == null)
319 throw new ArgumentNullException("match");
320
321 // Find a parameter match and return the first method with
322 // parameters that match the request.
323 foreach(MethodBase mb in match)
324 {
325 ParameterInfo[] parameters = mb.GetParameters();
326 if(ParametersMatch(parameters, types))
327 return mb;
328 }
329
330 return null;
331 }
332
333 public override PropertyInfo SelectProperty(
334 BindingFlags bindingAttr,
335 PropertyInfo[] match,
336 Type returnType,
337 Type[] indexes,
338 ParameterModifier[] modifiers)
339 {
340 if(match == null)
341 throw new ArgumentNullException("match");
342 foreach(PropertyInfo pi in match)
343 {
344 if(pi.GetType() == returnType &&
345 ParametersMatch(pi.GetIndexParameters(), indexes))
346 return pi;
347 }
348 return null;
349 }
350
351 public override object ChangeType(
352 object value,
353 Type myChangeType,
354 CultureInfo culture)
355 {
356 try
357 {
358 object newType;
359 newType = Convert.ChangeType(value, myChangeType);
360 return newType;
361 }
362 // Throw an InvalidCastException if the conversion cannot
363 // be done by the Convert.ChangeType method.
364 catch(InvalidCastException)
365 {
366 return null;
367 }
368 }
369
370 public override void ReorderArgumentArray(ref object[] args,
371 object state)
372 {
373 // No operation is needed here because BindToMethod does not
374 // reorder the args array. The most common implementation
375 // of this method is shown below.
376
377 // ((BinderState)state).args.CopyTo(args, 0);
378 }
379
380 // Returns true only if the type of each object in a matches
381 // the type of each corresponding object in b.
382 private bool ParametersMatch(ParameterInfo[] a, object[] b)
383 {
384 if(a.Length != b.Length)
385 return false;
386 for(int i = 0; i < a.Length; i++)
387 {
388 if(a[i].ParameterType != b[i].GetType())
389 return false;
390 }
391 return true;
392 }
393
394 // Returns true only if the type of each object in a matches
395 // the type of each corresponding entry in b.
396 private bool ParametersMatch(ParameterInfo[] a, Type[] b)
397 {
398 if(a.Length != b.Length)
399 return false;
400 for(int i = 0; i < a.Length; i++)
401 {
402 if(a[i].ParameterType != b[i])
403 return false;
404 }
405 return true;
406 }
407 }
408}
409
410
411InvokeMember 和 CreateInstance
412使用 Type..::.InvokeMember 可调用类型的成员。各个类（如 System.Activator 和 System.Reflection.Assembly）的 CreateInstance 方法是 InvokeMember 的特殊形式，它们可新建特定类型的实例。Binder 类用于在这些方法中进行重载决策和参数强制。
413
414下面的示例显示参数强制（类型转换）和成员选择的三种可能的组合。在第
1
种情况中，不需要任何参数强制或成员选择。在第
2
种情况中，只需要成员选择。在第
3
种情况中，只需要参数强制。
415
416C# 复制代码
417
public
class
CustomBinderDriver
418
{
419 public static void Main (string[] arguments)
420 {
421 Type t = typeof (CustomBinderDriver);
422 CustomBinder binder = new CustomBinder();
423 BindingFlags flags = BindingFlags.InvokeMethod|BindingFlags.Instance|
424 BindingFlags.Public|BindingFlags.Static;
425
426 // Case 1. Neither argument coercion nor member selection is needed.
427 args = new Object[] {};
428 t.InvokeMember ("PrintBob", flags, binder, null, args);
429
430 // Case 2. Only member selection is needed.
431 args = new Object[] {42};
432 t.InvokeMember ("PrintValue", flags, binder, null, args);
433
434 // Case 3. Only argument coercion is needed.
435 args = new Object[] {"5.5"};
436 t.InvokeMember ("PrintNumber", flags, binder, null, args);
437 }
438
439 public static void PrintBob ()
440 {
441 Console.WriteLine ("PrintBob");
442 }
443
444 public static void PrintValue (long value)
445 {
446 Console.WriteLine ("PrintValue ({0})", value);
447 }
448 public static void PrintValue (String value)
449 {
450 Console.WriteLine ("PrintValue\"{0}\")", value);
451 }
452
453 public static void PrintNumber (double value)
454 {
455 Console.WriteLine ("PrintNumber ({0})", value);
456 }
457}
458
459
460当多个成员具有相同的名称时，将需要重载决策。Binder..::.BindToMethod 和 Binder..::.BindToField 方法用于解析与单个成员的绑定。Binder.BindToMethod 还通过
get
和
set
属性访问器提供了属性解析。
461
462BindToMethod 返回要调用的 MethodBase；如果无法进行这种调用，则返回
null
引用（在 Visual Basic 中为 Nothing）。虽然 MethodBase 返回值通常是 match 参数中所包含的值之一，但它并不必如此。
463
464当存在 ByRef 参数时，调用方可能需要取回这些参数。因此，如果 BindToMethod 已经操作参数数组，Binder 会允许客户端将参数数组映射回它的初始形式。为了实现这一目的，必须向调用方保证参数的顺序不会改变。当按名称传递参数时，Binder 将重新排列参数数组，这就是调用方所见的参数。有关更多信息，请参见 Binder..::.ReorderArgumentArray。
465
466可用成员集包括在类型和任何基类型中定义的成员。如果指定 BindingFlags.NonPublic，将返回该成员集中具有任何可访问性的成员。如果未指定 BindingFlags.NonPublic，联编程序就必须强制可访问性规则。当指定 Public 或 NonPublic 绑定标志时，还必须指定 Instance 或 Static 绑定标志，否则不会返回任何成员。
467
468如果只有一个成员具有给定名称，则不必进行回调，而在该方法上进行绑定。代码示例的第
1
种情况说明了这一点：只有一个 PrintBob 方法可用，因此不需要进行回调。
469
470如果可用集中有多个成员，所有这些方法都将传递给 BindToMethod，它将选择正确的方法并将其返回。在代码示例的第
2
种情况下，有两个名为 PrintValue 的方法。对 BindToMethod 的调用将选择正确的方法。
471
472ChangeType 执行参数强制转换（类型转换），以便将实参转换为选定方法的形参的类型。即使类型完全匹配，也会为每个参数调用 ChangeType。
473
474在代码示例的第
3
种情况下，将类型为 String 值为“
5.5
”的实参传递给了具有类型为 Double 的形参的方法。要使调用成功，必须将字符串值“
5.5
”转换为
double
值。ChangeType 会执行此转换。
475
476ChangeType 仅执行无损或扩大强制，如下表所示。
477
478源类型
479 目标类型
480
481任何类型
482 它的基类型
483
484任何类型
485 它所实现的接口
486
487Char
488 UInt16、UInt32、Int32、UInt64、Int64、Single、Double
489
490Byte
491 Char、UInt16、Int16、UInt32、Int32、UInt64、Int64、Single、Double
492
493SByte
494 Int16、Int32、Int64、Single、Double
495
496UInt16
497 UInt32、Int32、UInt64、Int64、Single、Double
498
499Int16
500 Int32、Int64、Single、Double
501
502UInt32
503 UInt64、Int64、Single、Double
504
505Int32
506 Int64、Single、Double
507
508UInt64
509 Single、Double
510
511Int64
512 Single、Double
513
514Single
515 Double
516
517非引用类型
518 引用类型
519
520
521Type 类具有 Get 方法，这些方法使用 Binder 类型的参数来解析对特定成员的引用。Type..::.GetConstructor、Type..::.GetMethod 和 Type..::.GetProperty 通过为当前类型的特定成员提供签名信息来搜索该成员。对 Binder..::.SelectMethod 和 Binder..::.SelectProperty 进行回调以选择相应方法的给定签名信息。
522
反射提供语言编译器（如 Microsoft Visual Basic
2005
和 JScript）用于实现隐式后期绑定的基础结构。绑定是查找与唯一指定的类型相对应的声明（即实现）的过程。如果此过程是在运行时而不是在编译时发生，则称其为“后期绑定”。利用 Visual Basic
2005
，可以在代码中使用隐式后期绑定；Visual Basic 编译器会调用一个帮助器方法，该方法使用反射来获取对象类型。传递给帮助器方法的参数有助于在运行时调用正确的方法。这些参数包括：对其调用方法的实例（对象），被调用方法的名称（字符串），以及传递给被调用方法的参数（对象数组）。2
3
在下面的示例中，Visual Basic 编译器使用反射隐式地对其类型在编译时未知的对象调用方法。HelloWorld 类具有一个 PrintHello 方法，它输出与传递给 PrintHello 方法的某些文本串联的“Hello World”。在此示例中调用的 PrintHello 方法实际上是 Type..::.InvokeMember；Visual Basic 代码允许按照对象 (helloObj) 的类型在编译时已知（早期绑定）而不是在运行时已知（后期绑定）的方式来调用 PrintHello 方法。4
5
复制代码 6
Imports System7
Module Hello8
Sub Main()9
'
Sets up the variable.
10
Dim helloObj As Object11
'
Creates the object.
12
helloObj
=
new
HelloWorld()13
'
Invokes the print method as if it was early bound
14
'
even though it is really late bound.
15
helloObj.PrintHello(
"
Visual Basic Late Bound
"
)16
End Sub17
End Module18
19
20
自定义绑定21
除了由编译器隐式地用来进行后期绑定之外，反射还可以在代码中显式地用来完成后期绑定。22
23
公共语言运行库支持多种编程语言，但这些语言的绑定规则各不相同。在早期绑定的情况下，代码生成器可以完全控制此绑定。但是，当通过反射进行后期绑定时，必须用自定义绑定来控制绑定。Binder 类提供了对成员选择和调用的自定义控制。24
25
利用自定义绑定，您可以在运行时加载程序集，获取有关该程序集中类型的信息，然后对该类型调用方法或访问该类型的字段或属性。如果您在编译时（例如当对象类型依赖于用户输入时）不知道对象的类型，就可以使用这种方法。26
27
下面的示例说明不提供参数类型转换的简单的自定义联编程序。Simple_Type.dll 的代码位于示例主体之前。确保生成 Simple_Type.dll，然后在生成时在项目中包括对它的引用。28
29
Visual Basic 复制代码 30
'
Code for building Simple_Type.dll.
31
Imports System32
33
Namespace Simple_Type34
Public Class MySimpleClass35
Public Overloads Sub MyMethod(ByVal str As String, 36
ByVal i As Integer)37
Console.WriteLine(
"
MyMethod parameters: {0}, {1}
"
, str, i)38
End Sub
'
MyMethod
39
40
Public Overloads Sub MyMethod(ByVal str As String, 41
ByVal i As Integer, ByVal j As Integer)42
Console.WriteLine(
"
MyMethod parameters: {0}, {1}, {2}
"
, str, 43
i, j)44
End Sub
'
MyMethod
45
End Class
'
MySimpleClass
46
End Namespace
'
Simple_Type
47
48
Imports System49
Imports System.Reflection50
Imports System.Globalization51
Imports Simple_Type.Simple_Type52
53
Namespace Custom_Binder54
Class MyMainClass55
Shared Sub Main()56
'
Get the type of MySimpleClass.
57
Dim myType As Type
=
GetType(MySimpleClass)58
'
Get an instance of MySimpleClass.
59
Dim myInstance As New MySimpleClass()60
Dim myCustomBinder As New MyCustomBinder()61
'
Get the method information for the overload being sought.
62
Dim myMethod As MethodInfo
=
myType.GetMethod(
"
MyMethod
"
, 63
BindingFlags.Public Or BindingFlags.Instance, 64
myCustomBinder, New Type()
{GetType(String), 
myCustomBinder, New Type() 65
GetType(Integer)}
, Nothing)66
Console.WriteLine(myMethod.ToString())67
'
Invoke the overload.
68
myType.InvokeMember(
"
MyMethod
"
, BindingFlags.InvokeMethod, 69
myCustomBinder, myInstance, 70
New [Object]()
{"Testing", CInt(32)}
)71
End Sub
'
Main
72
End Class
'
MyMainClass
73
74
'
****************************************************
75
'
A simple custom binder that provides no
76
'
argument type conversion.
77
'
****************************************************
78
Class MyCustomBinder79
Inherits Binder80
81
Public Overrides Function BindToMethod(ByVal bindingAttr As 82
BindingFlags, ByVal match() As MethodBase, ByRef args() As 83
Object, ByVal modifiers() As ParameterModifier, ByVal 84
culture As CultureInfo, ByVal names() As String, ByRef 85
state As Object) As MethodBase86
If match Is Nothing Then87
Throw New ArgumentNullException(
"
match
"
)88
End If89
'
Arguments are not being reordered.
90
state
=
Nothing91
'
Find a parameter match and return the first method with
92
'
parameters that match the request.
93
Dim mb As MethodBase94
For Each mb In match95
Dim parameters As ParameterInfo()
=
mb.GetParameters()96
If ParametersMatch(parameters, args) Then97
Return mb98
End If99
Next mb100
Return Nothing101
End Function
'
BindToMethod
102
103
Public Overrides Function BindToField(ByVal bindingAttr As 104
BindingFlags, ByVal match() As FieldInfo, ByVal value As 105
Object, ByVal culture As CultureInfo) As FieldInfo106
If match Is Nothing Then107
Throw New ArgumentNullException(
"
match
"
)108
End If109
Dim fi As FieldInfo110
For Each fi In match111
If fi.GetType() Is value.GetType() Then112
Return fi113
End If114
Next fi115
Return Nothing116
End Function
'
BindToField
117
118
Public Overrides Function SelectMethod(ByVal bindingAttr As 119
BindingFlags, ByVal match() As MethodBase, ByVal types() As 120
Type, ByVal modifiers() As ParameterModifier) As 121
MethodBase122
If match Is Nothing Then123
Throw New ArgumentNullException(
"
match
"
)124
End If125
'
Find a parameter match and return the first method with
126
'
parameters that match the request.
127
Dim mb As MethodBase128
For Each mb In match129
Dim parameters As ParameterInfo()
=
mb.GetParameters()130
If ParametersMatch(parameters, types) Then131
Return mb132
End If133
Next mb134
Return Nothing135
End Function
'
SelectMethod
136
137
Public Overrides Function SelectProperty(ByVal bindingAttr As 138
BindingFlags, ByVal match() As PropertyInfo, ByVal returnType 139
As Type, ByVal indexes() As Type, ByVal modifiers() As 140
ParameterModifier) As PropertyInfo141
If match Is Nothing Then142
Throw New ArgumentNullException(
"
match
"
)143
End If144
Dim pi As PropertyInfo145
For Each pi In match146
If pi.GetType() Is returnType And 147
ParametersMatch(pi.GetIndexParameters(), indexes) Then148
Return pi149
End If150
Next pi151
Return Nothing152
End Function
'
SelectProperty
153
154
Public Overrides Function ChangeType(ByVal value As Object, 155
ByVal myChangeType As Type, ByVal culture As CultureInfo) 156
As Object157
Try158
Dim newType As Object159
newType
=
Convert.ChangeType(value, myChangeType)160
161
Return newType162
'
Throw an InvalidCastException if the conversion cannot
163
'
be done by the Convert.ChangeType method.
164
Catch165
End Try166
End Function
'
ChangeType
167
168
Public Overrides Sub ReorderArgumentArray(ByRef args() As Object, 169
ByVal state As Object)170
'
No operation is needed here because BindToMethod does not
171
'
reorder the args array. The most common implementation
172
'
of this method is shown below.
173
174
'
((BinderState)state).args.CopyTo(args, 0);
175
End Sub
'
ReorderArgumentArray
176
177
'
Returns true only if the type of each object in a matches
178
'
the type of each corresponding object in b.
179
Private Overloads Function ParametersMatch(ByVal a() As 180
ParameterInfo, ByVal b() As Object) As Boolean181
If a.Length
<>
b.Length Then182
Return False183
End If184
Dim i As Integer185
For i
=
0
To a.Length
-
1
186
If Not (a(i).ParameterType Is b(i).GetType()) Then187
Return False188
End If189
Next i190
Return True191
End Function
'
ParametersMatch
192
193
'
Returns true only if the type of each object in a matches
194
'
the type of each corresponding entry in b.
195
Private Overloads Function ParametersMatch(ByVal a() As 196
ParameterInfo, ByVal b() As Type) As Boolean197
If a.Length
<>
b.Length Then198
Return False199
End If200
Dim i As Integer201
For i
=
0
To a.Length
-
1
202
If Not (a(i).ParameterType Is b(i)) Then203
Return False204
End If205
Next i206
Return True207
End Function
'
ParametersMatch
208
End Class
'
MyCustomBinder
209
End Namespace
'
Custom_Binder
210
211
212
213
214
C# 复制代码 215
//
Code for building SimpleType.dll.
216
using
System;217
218
namespace
Simple_Type219
{220
public class MySimpleClass221
{
222
public void MyMethod(string str, int i)223
{224
Console.WriteLine("MyMethod parameters: {0}, {1}", str, i);225
}226
227
public void MyMethod(string str, int i, int j)228
{229
Console.WriteLine("MyMethod parameters: {0}, {1}, {2}", 230
str, i, j);231
}232
}233
}
234
235
236
using
System;237
using
System.Reflection;238
using
System.Globalization;239
using
Simple_Type;240
namespace
Custom_Binder241
{242
class MyMainClass243
{244
static void Main()245
{246
// Get the type of MySimpleClass.247
Type myType = typeof(MySimpleClass);248
249
// Get an instance of MySimpleClass.250
MySimpleClass myInstance = new MySimpleClass();251
MyCustomBinder myCustomBinder = new MyCustomBinder();252
253
// Get the method information for the particular overload 254
// being sought.255
MethodInfo myMethod = myType.GetMethod("MyMethod", 256
BindingFlags.Public | BindingFlags.Instance,257
myCustomBinder, new Type[] {typeof(string), 258
typeof(int)}, null);259
Console.WriteLine(myMethod.ToString());260
261
// Invoke the overload.262
myType.InvokeMember("MyMethod", BindingFlags.InvokeMethod, 263
myCustomBinder, myInstance, 264
new Object[] {"Testing", (int)32});265
}266
}267
268
//****************************************************269
// A simple custom binder that provides no270
// argument type conversion.271
//****************************************************272
class MyCustomBinder : Binder273
{274
public override MethodBase BindToMethod(275
BindingFlags bindingAttr,276
MethodBase[] match,277
ref object[] args,278
ParameterModifier[] modifiers,279
CultureInfo culture,280
string[] names,281
out object state)282
{283
if(match == null)284
throw new ArgumentNullException("match");285
// Arguments are not being reordered.286
state = null;287
// Find a parameter match and return the first method with288
// parameters that match the request.289
foreach(MethodBase mb in match)290
{291
ParameterInfo[] parameters = mb.GetParameters();292
293
if(ParametersMatch(parameters, args))294
return mb;295
}296
return null;297
}298
299
public override FieldInfo BindToField(BindingFlags bindingAttr, 300
FieldInfo[] match, object value, CultureInfo culture)301
{302
if(match == null)303
throw new ArgumentNullException("match");304
foreach(FieldInfo fi in match)305
{306
if(fi.GetType() == value.GetType())307
return fi;308
}309
return null;310
}311
312
public override MethodBase SelectMethod(313
BindingFlags bindingAttr,314
MethodBase[] match,315
Type[] types,316
ParameterModifier[] modifiers)317
{318
if(match == null)319
throw new ArgumentNullException("match");320
321
// Find a parameter match and return the first method with322
// parameters that match the request.323
foreach(MethodBase mb in match)324
{325
ParameterInfo[] parameters = mb.GetParameters();326
if(ParametersMatch(parameters, types))327
return mb;328
}329
330
return null;331
}332
333
public override PropertyInfo SelectProperty(334
BindingFlags bindingAttr,335
PropertyInfo[] match,336
Type returnType,337
Type[] indexes,338
ParameterModifier[] modifiers)339
{340
if(match == null)341
throw new ArgumentNullException("match");342
foreach(PropertyInfo pi in match)343
{344
if(pi.GetType() == returnType && 345
ParametersMatch(pi.GetIndexParameters(), indexes))346
return pi;347
}348
return null;349
}350
351
public override object ChangeType(352
object value,353
Type myChangeType,354
CultureInfo culture)355
{356
try357
{358
object newType;359
newType = Convert.ChangeType(value, myChangeType);360
return newType;361
}362
// Throw an InvalidCastException if the conversion cannot363
// be done by the Convert.ChangeType method.364
catch(InvalidCastException)365
{366
return null;367
}368
}369
370
public override void ReorderArgumentArray(ref object[] args, 371
object state)372
{373
// No operation is needed here because BindToMethod does not374
// reorder the args array. The most common implementation375
// of this method is shown below.376
377
// ((BinderState)state).args.CopyTo(args, 0);378
}379
380
// Returns true only if the type of each object in a matches381
// the type of each corresponding object in b.382
private bool ParametersMatch(ParameterInfo[] a, object[] b)383
{384
if(a.Length != b.Length)385
return false;386
for(int i = 0; i < a.Length; i++)387
{388
if(a[i].ParameterType != b[i].GetType())389
return false;390
}391
return true;392
}393
394
// Returns true only if the type of each object in a matches395
// the type of each corresponding entry in b.396
private bool ParametersMatch(ParameterInfo[] a, Type[] b)397
{398
if(a.Length != b.Length)399
return false;400
for(int i = 0; i < a.Length; i++)401
{402
if(a[i].ParameterType != b[i])403
return false;404
}405
return true;406
}407
}408
}
409
410
411
InvokeMember 和 CreateInstance412
使用 Type..::.InvokeMember 可调用类型的成员。各个类（如 System.Activator 和 System.Reflection.Assembly）的 CreateInstance 方法是 InvokeMember 的特殊形式，它们可新建特定类型的实例。Binder 类用于在这些方法中进行重载决策和参数强制。413
414
下面的示例显示参数强制（类型转换）和成员选择的三种可能的组合。在第
1
种情况中，不需要任何参数强制或成员选择。在第
2
种情况中，只需要成员选择。在第
3
种情况中，只需要参数强制。415
416
C# 复制代码 417
public
class
CustomBinderDriver418
{419
public static void Main (string[] arguments)420
{421
Type t = typeof (CustomBinderDriver);422
CustomBinder binder = new CustomBinder();423
BindingFlags flags = BindingFlags.InvokeMethod|BindingFlags.Instance|424
BindingFlags.Public|BindingFlags.Static;425
426
// Case 1. Neither argument coercion nor member selection is needed.427
args = new Object[] {};428
t.InvokeMember ("PrintBob", flags, binder, null, args);429
430
// Case 2. Only member selection is needed.431
args = new Object[] {42};432
t.InvokeMember ("PrintValue", flags, binder, null, args);433
434
// Case 3. Only argument coercion is needed.435
args = new Object[] {"5.5"};436
t.InvokeMember ("PrintNumber", flags, binder, null, args);437
}438
439
public static void PrintBob ()440
{441
Console.WriteLine ("PrintBob");442
}443
444
public static void PrintValue (long value)445
{446
Console.WriteLine ("PrintValue ({0})", value);447
}448
public static void PrintValue (String value)449
{450
Console.WriteLine ("PrintValue\"{0}\")", value);451
}452
453
public static void PrintNumber (double value)454
{455
Console.WriteLine ("PrintNumber ({0})", value);456
}457
}
458
459
460
当多个成员具有相同的名称时，将需要重载决策。Binder..::.BindToMethod 和 Binder..::.BindToField 方法用于解析与单个成员的绑定。Binder.BindToMethod 还通过
get
和
set
属性访问器提供了属性解析。461
462
BindToMethod 返回要调用的 MethodBase；如果无法进行这种调用，则返回
null
引用（在 Visual Basic 中为 Nothing）。虽然 MethodBase 返回值通常是 match 参数中所包含的值之一，但它并不必如此。463
464
当存在 ByRef 参数时，调用方可能需要取回这些参数。因此，如果 BindToMethod 已经操作参数数组，Binder 会允许客户端将参数数组映射回它的初始形式。为了实现这一目的，必须向调用方保证参数的顺序不会改变。当按名称传递参数时，Binder 将重新排列参数数组，这就是调用方所见的参数。有关更多信息，请参见 Binder..::.ReorderArgumentArray。465
466
可用成员集包括在类型和任何基类型中定义的成员。如果指定 BindingFlags.NonPublic，将返回该成员集中具有任何可访问性的成员。如果未指定 BindingFlags.NonPublic，联编程序就必须强制可访问性规则。当指定 Public 或 NonPublic 绑定标志时，还必须指定 Instance 或 Static 绑定标志，否则不会返回任何成员。467
468
如果只有一个成员具有给定名称，则不必进行回调，而在该方法上进行绑定。代码示例的第
1
种情况说明了这一点：只有一个 PrintBob 方法可用，因此不需要进行回调。469
470
如果可用集中有多个成员，所有这些方法都将传递给 BindToMethod，它将选择正确的方法并将其返回。在代码示例的第
2
种情况下，有两个名为 PrintValue 的方法。对 BindToMethod 的调用将选择正确的方法。471
472
ChangeType 执行参数强制转换（类型转换），以便将实参转换为选定方法的形参的类型。即使类型完全匹配，也会为每个参数调用 ChangeType。473
474
在代码示例的第
3
种情况下，将类型为 String 值为“
5.5
”的实参传递给了具有类型为 Double 的形参的方法。要使调用成功，必须将字符串值“
5.5
”转换为
double
值。ChangeType 会执行此转换。475
476
ChangeType 仅执行无损或扩大强制，如下表所示。477
478
源类型479
目标类型480
481
任何类型482
它的基类型483
484
任何类型485
它所实现的接口486
487
Char488
UInt16、UInt32、Int32、UInt64、Int64、Single、Double489
490
Byte491
Char、UInt16、Int16、UInt32、Int32、UInt64、Int64、Single、Double492
493
SByte494
Int16、Int32、Int64、Single、Double495
496
UInt16497
UInt32、Int32、UInt64、Int64、Single、Double498
499
Int16500
Int32、Int64、Single、Double501
502
UInt32503
UInt64、Int64、Single、Double504
505
Int32506
Int64、Single、Double507
508
UInt64509
Single、Double510
511
Int64512
Single、Double513
514
Single515
Double516
517
非引用类型518
引用类型519
520
521
Type 类具有 Get 方法，这些方法使用 Binder 类型的参数来解析对特定成员的引用。Type..::.GetConstructor、Type..::.GetMethod 和 Type..::.GetProperty 通过为当前类型的特定成员提供签名信息来搜索该成员。对 Binder..::.SelectMethod 和 Binder..::.SelectProperty 进行回调以选择相应方法的给定签名信息。522