仅反射加载上下文允许您检查为其他平台或其他版本的 .NET 编译的程序集。 只能检查加载到此上下文中的代码;无法执行。 这意味着无法创建对象，因为无法执行构造函数。 由于无法执行代码，因此不会自动加载依赖项。 如果需要检查它们，则必须自行加载它们。
将程序集加载到仅反射加载上下文中
ReflectionOnlyLoad(String)方法重载来加载程序集，给定其显示名称，或使用ReflectionOnlyLoadFrom方法给定其路径来加载程序集。 如果程序集是二进制映像，请使用 ReflectionOnlyLoad(Byte[]) 方法重载。
注释
不能使用仅反射上下文从执行上下文中版本以外的 .NET Framework 版本加载 mscorlib.dll 版本。
如果程序集具有依赖项，则 ReflectionOnlyLoad 该方法不会加载它们。 如果需要检查它们，则必须自行加载它们。
使用程序集的 ReflectionOnly 属性来确定该程序集是否已加载到仅限反射上下文中。
如果特性已应用于程序集或程序集中的类型，请使用 CustomAttributeData 类检查这些属性，以确保不会尝试在仅反射上下文中执行代码。 要使用适当的CustomAttributeData.GetCustomAttributes方法重载来获取表示CustomAttributeData应用于程序集、成员、模块或参数的属性对象。
注释
应用于程序集或其内容的属性可能在程序集中定义，也可以在加载到仅反射上下文的另一个程序集中定义它们。 无法提前判断属性的定义位置。
示例
下面的代码示例演示如何检查应用于加载到仅反射上下文中的程序集的属性。
该代码示例使用两个构造函数和一个属性定义自定义属性。 该特性应用于程序集、程序集中声明的类型、类型的方法以及方法的参数。 在执行时，程序集将自身加载到仅供反射使用的上下文中，并显示应用于它以及其包含的类型和成员的自定义属性信息。
注释
为了简化代码示例，程序集将加载并检查自身。 通常，你不会期望在执行上下文和仅供反射的上下文中加载同一程序集。
using namespace System;
using namespace System::Reflection;
using namespace System::Collections::Generic;
using namespace System::Collections::ObjectModel;
// An enumeration used by the ExampleAttribute class.
public enum class ExampleKind
{
FirstKind, SecondKind, ThirdKind, FourthKind
};
// An example attribute. The attribute can be applied to all
// targets, from assemblies to parameters.
//
[AttributeUsage(AttributeTargets::All)]
public ref class ExampleAttribute: public Attribute
{
private:
// Data for properties.
ExampleKind kindValue;
String^ noteValue;
array<String^>^ arrayStrings;
array<int>^ arrayNumbers;
// Constructors.
void ExampleAttributeInitialize( ExampleKind initKind, array<String^>^ initStrings )
{
kindValue = initKind;
arrayStrings = initStrings;
}
public:
ExampleAttribute()
{
ExampleAttributeInitialize( ExampleKind::FirstKind, nullptr );
}
ExampleAttribute( ExampleKind initKind )
{
ExampleAttributeInitialize( initKind, nullptr );
}
ExampleAttribute( ExampleKind initKind, array<String^>^ initStrings )
{
ExampleAttributeInitialize( initKind, initStrings );
}
// Properties. The Note and Numbers properties must be read/write, so they
// can be used as named parameters.
//
property ExampleKind Kind
{
ExampleKind get()
{
return kindValue;
}
}
property array<String^>^ Strings
{
array<String^>^ get()
{
return arrayStrings;
}
}
property String^ Note
{
String^ get()
{
return noteValue;
}
void set( String^ value )
{
noteValue = value;
}
}
property array<int>^ Numbers
{
array<int>^ get()
{
return arrayNumbers;
}
void set( array<int>^ value )
{
arrayNumbers = value;
}
}
};
// The example attribute is applied to the assembly.
[assembly:Example(ExampleKind::ThirdKind,Note="This is a note on the assembly.")];
// The example attribute is applied to the test class.
//
[Example(ExampleKind::SecondKind,
gcnew array<String^> { "String array argument, line 1",
"String array argument, line 2",
"String array argument, line 3" },
Note="This is a note on the class.",
Numbers = gcnew array<int> { 53, 57, 59 })]
public ref class Test
{
public:
// The example attribute is applied to a method, using the
// parameterless constructor and supplying a named argument.
// The attribute is also applied to the method parameter.
//
[Example(Note="This is a note on a method.")]
void TestMethod( [Example] Object^ arg ){}
// Main() gets objects representing the assembly, the test
// type, the test method, and the method parameter. Custom
// attribute data is displayed for each of these.
//
static void Main()
{
Assembly^ assembly = Assembly::ReflectionOnlyLoad( "Source" );
Type^ t = assembly->GetType( "Test" );
MethodInfo^ m = t->GetMethod( "TestMethod" );
array<ParameterInfo^>^p = m->GetParameters();
Console::WriteLine( "\r\nAttributes for assembly: '{0}'", assembly );
ShowAttributeData( CustomAttributeData::GetCustomAttributes( assembly ) );
Console::WriteLine( "\r\nAttributes for type: '{0}'", t );
ShowAttributeData( CustomAttributeData::GetCustomAttributes( t ) );
Console::WriteLine( "\r\nAttributes for member: '{0}'", m );
ShowAttributeData( CustomAttributeData::GetCustomAttributes( m ) );
Console::WriteLine( "\r\nAttributes for parameter: '{0}'", p );
ShowAttributeData( CustomAttributeData::GetCustomAttributes( p[ 0 ] ) );
}
private:
static void ShowValueOrArray(CustomAttributeTypedArgument^ cata)
{
if (cata->Value->GetType() == ReadOnlyCollection<CustomAttributeTypedArgument>::typeid)
{
Console::WriteLine(" Array of '{0}':", cata->ArgumentType);
for each (CustomAttributeTypedArgument^ cataElement in
(ReadOnlyCollection<CustomAttributeTypedArgument>^) cata->Value)
{
Console::WriteLine(" Type: '{0}' Value: '{1}'",
cataElement->ArgumentType, cataElement->Value);
}
}
else
{
Console::WriteLine( " Type: '{0}' Value: '{1}'",
cata->ArgumentType, cata->Value );
}
}
static void ShowAttributeData( IList< CustomAttributeData^ >^ attributes )
{
for each ( CustomAttributeData^ cad in attributes )
{
Console::WriteLine( " {0}", cad );
Console::WriteLine( " Constructor: '{0}'", cad->Constructor );
Console::WriteLine( " Constructor arguments:" );
for each ( CustomAttributeTypedArgument^ cata in cad->ConstructorArguments )
{
ShowValueOrArray(cata);
}
Console::WriteLine( " Named arguments:" );
for each ( CustomAttributeNamedArgument cana in cad->NamedArguments )
{
Console::WriteLine( " MemberInfo: '{0}'", cana.MemberInfo );
ShowValueOrArray(cana.TypedValue);
}
}
}
};
int main()
{
Test::Main();
}
/* This code example produces output similar to the following:
Attributes for assembly: 'source, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null'
[System.Runtime.CompilerServices.CompilationRelaxationsAttribute((Int32)8)]
Constructor: 'Void .ctor(Int32)'
Constructor arguments:
Type: 'System.Int32' Value: '8'
Named arguments:
[System.Runtime.CompilerServices.RuntimeCompatibilityAttribute(WrapNonExceptionThrows = True)]
Constructor: 'Void .ctor()'
Constructor arguments:
Named arguments:
MemberInfo: 'Boolean WrapNonExceptionThrows'
Type: 'System.Boolean' Value: 'True'
[ExampleAttribute((ExampleKind)2, Note = "This is a note on the assembly.")]
Constructor: 'Void .ctor(ExampleKind)'
Constructor arguments:
Type: 'ExampleKind' Value: '2'
Named arguments:
MemberInfo: 'System.String Note'
Type: 'System.String' Value: 'This is a note on the assembly.'
Attributes for type: 'Test'
[ExampleAttribute((ExampleKind)1, new String[3] { "String array argument, line 1", "String array argument, line 2", "String array argument, line 3" }, Note = "This is a note on the class.", Numbers = new Int32[3] { 53, 57, 59 })]
Constructor: 'Void .ctor(ExampleKind, System.String[])'
Constructor arguments:
Type: 'ExampleKind' Value: '1'
Array of 'System.String[]':
Type: 'System.String' Value: 'String array argument, line 1'
Type: 'System.String' Value: 'String array argument, line 2'
Type: 'System.String' Value: 'String array argument, line 3'
Named arguments:
MemberInfo: 'System.String Note'
Type: 'System.String' Value: 'This is a note on the class.'
MemberInfo: 'Int32[] Numbers'
Array of 'System.Int32[]':
Type: 'System.Int32' Value: '53'
Type: 'System.Int32' Value: '57'
Type: 'System.Int32' Value: '59'
Attributes for member: 'Void TestMethod(System.Object)'
[ExampleAttribute(Note = "This is a note on a method.")]
Constructor: 'Void .ctor()'
Constructor arguments:
Named arguments:
MemberInfo: 'System.String Note'
Type: 'System.String' Value: 'This is a note on a method.'
Attributes for parameter: 'System.Object arg'
[ExampleAttribute()]
Constructor: 'Void .ctor()'
Constructor arguments:
Named arguments:
*/
using System;
using System.Reflection;
using System.Collections.Generic;
using System.Collections.ObjectModel;
// The example attribute is applied to the assembly.
[assembly:Example(ExampleKind.ThirdKind, Note="This is a note on the assembly.")]
// An enumeration used by the ExampleAttribute class.
public enum ExampleKind
{
FirstKind,
SecondKind,
ThirdKind,
FourthKind
};
// An example attribute. The attribute can be applied to all
// targets, from assemblies to parameters.
//
[AttributeUsage(AttributeTargets.All)]
public class ExampleAttribute : Attribute
{
// Data for properties.
private ExampleKind kindValue;
private string noteValue;
private string[] arrayStrings;
private int[] arrayNumbers;
// Constructors. The parameterless constructor (.ctor) calls
// the constructor that specifies ExampleKind and an array of
// strings, and supplies the default values.
//
public ExampleAttribute(ExampleKind initKind, string[] initStrings)
{
kindValue = initKind;
arrayStrings = initStrings;
}
public ExampleAttribute(ExampleKind initKind) : this(initKind, null) {}
public ExampleAttribute() : this(ExampleKind.FirstKind, null) {}
// Properties. The Note and Numbers properties must be read/write, so they
// can be used as named parameters.
//
public ExampleKind Kind { get { return kindValue; }}
public string[] Strings { get { return arrayStrings; }}
public string Note
{
get { return noteValue; }
set { noteValue = value; }
}
public int[] Numbers
{
get { return arrayNumbers; }
set { arrayNumbers = value; }
}
}
// The example attribute is applied to the test class.
//
[Example(ExampleKind.SecondKind,
new string[] { "String array argument, line 1",
"String array argument, line 2",
"String array argument, line 3" },
Note="This is a note on the class.",
Numbers = new int[] { 53, 57, 59 })]
public class Test
{
// The example attribute is applied to a method, using the
// parameterless constructor and supplying a named argument.
// The attribute is also applied to the method parameter.
//
[Example(Note="This is a note on a method.")]
public void TestMethod([Example] object arg) { }
// Main() gets objects representing the assembly, the test
// type, the test method, and the method parameter. Custom
// attribute data is displayed for each of these.
//
public static void Main()
{
Assembly asm = Assembly.ReflectionOnlyLoad("Source");
Type t = asm.GetType("Test");
MethodInfo m = t.GetMethod("TestMethod");
ParameterInfo[] p = m.GetParameters();
Console.WriteLine($"\r\nAttributes for assembly: '{asm}'");
ShowAttributeData(CustomAttributeData.GetCustomAttributes(asm));
Console.WriteLine($"\r\nAttributes for type: '{t}'");
ShowAttributeData(CustomAttributeData.GetCustomAttributes(t));
Console.WriteLine($"\r\nAttributes for member: '{m}'");
ShowAttributeData(CustomAttributeData.GetCustomAttributes(m));
Console.WriteLine($"\r\nAttributes for parameter: '{p}'");
ShowAttributeData(CustomAttributeData.GetCustomAttributes(p[0]));
}
private static void ShowAttributeData(
IList<CustomAttributeData> attributes)
{
foreach( CustomAttributeData cad in attributes )
{
Console.WriteLine($" {cad}");
Console.WriteLine($" Constructor: '{cad.Constructor}'");
Console.WriteLine(" Constructor arguments:");
foreach( CustomAttributeTypedArgument cata
in cad.ConstructorArguments )
{
ShowValueOrArray(cata);
}
Console.WriteLine(" Named arguments:");
foreach( CustomAttributeNamedArgument cana
in cad.NamedArguments )
{
Console.WriteLine($" MemberInfo: '{cana.MemberInfo}'");
ShowValueOrArray(cana.TypedValue);
}
}
}
private static void ShowValueOrArray(CustomAttributeTypedArgument cata)
{
if (cata.Value.GetType() == typeof(ReadOnlyCollection<CustomAttributeTypedArgument>))
{
Console.WriteLine($" Array of '{cata.ArgumentType}':");
foreach (CustomAttributeTypedArgument cataElement in
(ReadOnlyCollection<CustomAttributeTypedArgument>) cata.Value)
{
Console.WriteLine($" Type: '{cataElement.ArgumentType}' Value: '{cataElement.Value}'");
}
}
else
{
Console.WriteLine($" Type: '{cata.ArgumentType}' Value: '{cata.Value}'");
}
}
}
/* This code example produces output similar to the following:
Attributes for assembly: 'source, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null'
[System.Runtime.CompilerServices.CompilationRelaxationsAttribute((Int32)8)]
Constructor: 'Void .ctor(Int32)'
Constructor arguments:
Type: 'System.Int32' Value: '8'
Named arguments:
[System.Runtime.CompilerServices.RuntimeCompatibilityAttribute(WrapNonExceptionThrows = True)]
Constructor: 'Void .ctor()'
Constructor arguments:
Named arguments:
MemberInfo: 'Boolean WrapNonExceptionThrows'
Type: 'System.Boolean' Value: 'True'
[ExampleAttribute((ExampleKind)2, Note = "This is a note on the assembly.")]
Constructor: 'Void .ctor(ExampleKind)'
Constructor arguments:
Type: 'ExampleKind' Value: '2'
Named arguments:
MemberInfo: 'System.String Note'
Type: 'System.String' Value: 'This is a note on the assembly.'
Attributes for type: 'Test'
[ExampleAttribute((ExampleKind)1, new String[3] { "String array argument, line 1", "String array argument, line 2", "String array argument, line 3" }, Note = "This is a note on the class.", Numbers = new Int32[3] { 53, 57, 59 })]
Constructor: 'Void .ctor(ExampleKind, System.String[])'
Constructor arguments:
Type: 'ExampleKind' Value: '1'
Array of 'System.String[]':
Type: 'System.String' Value: 'String array argument, line 1'
Type: 'System.String' Value: 'String array argument, line 2'
Type: 'System.String' Value: 'String array argument, line 3'
Named arguments:
MemberInfo: 'System.String Note'
Type: 'System.String' Value: 'This is a note on the class.'
MemberInfo: 'Int32[] Numbers'
Array of 'System.Int32[]':
Type: 'System.Int32' Value: '53'
Type: 'System.Int32' Value: '57'
Type: 'System.Int32' Value: '59'
Attributes for member: 'Void TestMethod(System.Object)'
[ExampleAttribute(Note = "This is a note on a method.")]
Constructor: 'Void .ctor()'
Constructor arguments:
Named arguments:
MemberInfo: 'System.String Note'
Type: 'System.String' Value: 'This is a note on a method.'
Attributes for parameter: 'System.Object arg'
[ExampleAttribute()]
Constructor: 'Void .ctor()'
Constructor arguments:
Named arguments:
*/
Imports System.Reflection
Imports System.Collections.Generic
Imports System.Collections.ObjectModel
' The example attribute is applied to the assembly.
<Assembly: Example(ExampleKind.ThirdKind, Note:="This is a note on the assembly.")>
' An enumeration used by the ExampleAttribute class.
Public Enum ExampleKind
FirstKind
SecondKind
ThirdKind
FourthKind
End Enum
' An example attribute. The attribute can be applied to all
' targets, from assemblies to parameters.
'
<AttributeUsage(AttributeTargets.All)> _
Public Class ExampleAttribute
Inherits Attribute
' Data for properties.
Private kindValue As ExampleKind
Private noteValue As String
Private arrayStrings() As String
Private arrayNumbers() As Integer
' Constructors. The parameterless constructor (.ctor) calls
' the constructor that specifies ExampleKind and an array of
' strings, and supplies the default values.
'
Public Sub New(ByVal initKind As ExampleKind, ByVal initStrings() As String)
kindValue = initKind
arrayStrings = initStrings
End Sub
Public Sub New(ByVal initKind As ExampleKind)
Me.New(initKind, Nothing)
End Sub
Public Sub New()
Me.New(ExampleKind.FirstKind, Nothing)
End Sub
' Properties. The Note and Numbers properties must be read/write, so they
' can be used as named parameters.
'
Public ReadOnly Property Kind As ExampleKind
Get
Return kindValue
End Get
End Property
Public ReadOnly Property Strings As String()
Get
Return arrayStrings
End Get
End Property
Public Property Note As String
Get
Return noteValue
End Get
Set
noteValue = value
End Set
End Property
Public Property Numbers As Integer()
Get
Return arrayNumbers
End Get
Set
arrayNumbers = value
End Set
End Property
End Class
' The example attribute is applied to the test class.
'
<Example(ExampleKind.SecondKind, _
New String() {"String array argument, line 1", _
"String array argument, line 2", _
"String array argument, line 3"}, _
Note:="This is a note on the class.", _
Numbers:=New Integer() {53, 57, 59})> _
Public Class Test
' The example attribute is applied to a method, using the
' parameterless constructor and supplying a named argument.
' The attribute is also applied to the method parameter.
'
<Example(Note:="This is a note on a method.")> _
Public Sub TestMethod(<Example()> ByVal arg As Object)
End Sub
' Sub Main gets objects representing the assembly, the test
' type, the test method, and the method parameter. Custom
' attribute data is displayed for each of these.
'
Public Shared Sub Main()
Dim asm As [Assembly] = Assembly.ReflectionOnlyLoad("source")
Dim t As Type = asm.GetType("Test")
Dim m As MethodInfo = t.GetMethod("TestMethod")
Dim p() As ParameterInfo = m.GetParameters()
Console.WriteLine(vbCrLf & "Attributes for assembly: '{0}'", asm)
ShowAttributeData(CustomAttributeData.GetCustomAttributes(asm))
Console.WriteLine(vbCrLf & "Attributes for type: '{0}'", t)
ShowAttributeData(CustomAttributeData.GetCustomAttributes(t))
Console.WriteLine(vbCrLf & "Attributes for member: '{0}'", m)
ShowAttributeData(CustomAttributeData.GetCustomAttributes(m))
Console.WriteLine(vbCrLf & "Attributes for parameter: '{0}'", p)
ShowAttributeData(CustomAttributeData.GetCustomAttributes(p(0)))
End Sub
Private Shared Sub ShowAttributeData( _
ByVal attributes As IList(Of CustomAttributeData))
For Each cad As CustomAttributeData _
In CType(attributes, IEnumerable(Of CustomAttributeData))
Console.WriteLine(" {0}", cad)
Console.WriteLine(" Constructor: '{0}'", cad.Constructor)
Console.WriteLine(" Constructor arguments:")
For Each cata As CustomAttributeTypedArgument _
In CType(cad.ConstructorArguments, IEnumerable(Of CustomAttributeTypedArgument))
ShowValueOrArray(cata)
Next
Console.WriteLine(" Named arguments:")
For Each cana As CustomAttributeNamedArgument _
In CType(cad.NamedArguments, IEnumerable(Of CustomAttributeNamedArgument))
Console.WriteLine(" MemberInfo: '{0}'", _
cana.MemberInfo)
ShowValueOrArray(cana.TypedValue)
Next
Next
End Sub
Private Shared Sub ShowValueOrArray(ByVal cata As CustomAttributeTypedArgument)
If cata.Value.GetType() Is GetType(ReadOnlyCollection(Of CustomAttributeTypedArgument)) Then
Console.WriteLine(" Array of '{0}':", cata.ArgumentType)
For Each cataElement As CustomAttributeTypedArgument In cata.Value
Console.WriteLine(" Type: '{0}' Value: '{1}'", _
cataElement.ArgumentType, cataElement.Value)
Next
Else
Console.WriteLine(" Type: '{0}' Value: '{1}'", _
cata.ArgumentType, cata.Value)
End If
End Sub
End Class
' This code example produces output similar to the following:
'
'Attributes for assembly: 'source, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null'
' [System.Runtime.CompilerServices.CompilationRelaxationsAttribute((Int32)8)]
' Constructor: 'Void .ctor(Int32)'
' Constructor arguments:
' Type: 'System.Int32' Value: '8'
' Named arguments:
' [System.Runtime.CompilerServices.RuntimeCompatibilityAttribute(WrapNonExceptionThrows = True)]
' Constructor: 'Void .ctor()'
' Constructor arguments:
' Named arguments:
' MemberInfo: 'Boolean WrapNonExceptionThrows'
' Type: 'System.Boolean' Value: 'True'
' [ExampleAttribute((ExampleKind)2, Note = "This is a note on the assembly.")]
' Constructor: 'Void .ctor(ExampleKind)'
' Constructor arguments:
' Type: 'ExampleKind' Value: '2'
' Named arguments:
' MemberInfo: 'System.String Note'
' Type: 'System.String' Value: 'This is a note on the assembly.'
'
'Attributes for type: 'Test'
' [ExampleAttribute((ExampleKind)1, new String[3] { "String array argument, line 1", "String array argument, line 2", "String array argument, line 3" }, Note = "This is a note on the class.", Numbers = new Int32[3] { 53, 57, 59 })]
' Constructor: 'Void .ctor(ExampleKind, System.String[])'
' Constructor arguments:
' Type: 'ExampleKind' Value: '1'
' Array of 'System.String[]':
' Type: 'System.String' Value: 'String array argument, line 1'
' Type: 'System.String' Value: 'String array argument, line 2'
' Type: 'System.String' Value: 'String array argument, line 3'
' Named arguments:
' MemberInfo: 'System.String Note'
' Type: 'System.String' Value: 'This is a note on the class.'
' MemberInfo: 'Int32[] Numbers'
' Array of 'System.Int32[]':
' Type: 'System.Int32' Value: '53'
' Type: 'System.Int32' Value: '57'
' Type: 'System.Int32' Value: '59'
'
'Attributes for member: 'Void TestMethod(System.Object)'
' [ExampleAttribute(Note = "This is a note on a method.")]
' Constructor: 'Void .ctor()'
' Constructor arguments:
' Named arguments:
' MemberInfo: 'System.String Note'
' Type: 'System.String' Value: 'This is a note on a method.'
'
'Attributes for parameter: 'System.Object arg'
' [ExampleAttribute()]
' Constructor: 'Void .ctor()'
' Constructor arguments:
' Named arguments:
