FieldInfo.GetFieldFromHandle 方法

Source:

FieldInfo.CoreCLR.cs

Source:

FieldInfo.CoreCLR.cs

Source:

FieldInfo.CoreCLR.cs

public:
 static System::Reflection::FieldInfo ^ GetFieldFromHandle(RuntimeFieldHandle handle);

public static System.Reflection.FieldInfo GetFieldFromHandle (RuntimeFieldHandle handle);

static member GetFieldFromHandle : RuntimeFieldHandle -> System.Reflection.FieldInfo

Public Shared Function GetFieldFromHandle (handle As RuntimeFieldHandle) As FieldInfo

参数

返回

FieldInfo 对象，表示由 handle 指定的字段。

例外

示例

下面的代码示例使用 Type.GetFields 方法获取FieldInfo类型字段的对象，获取RuntimeFieldHandle每个字段的结构，然后使用 方法的GetFieldFromHandle此重载从句柄检索FieldInfo对象。

using namespace System;
using namespace System::Reflection;

public ref class FieldInfo_GetFieldFromHandle
{
public:
   String^ x;
   Char y;
   float a;
   int b;
};

int main()
{
   // Get the type of the FieldInfo_GetFieldFromHandle class.
   Type^ myType = FieldInfo_GetFieldFromHandle::typeid;

   // Get the fields of the FieldInfo_GetFieldFromHandle class.
   array<FieldInfo^>^myFieldInfoArray = myType->GetFields();
   Console::WriteLine( "\nThe field information of the declared  fields x, y, a, and b is:\n" );
   RuntimeFieldHandle myRuntimeFieldHandle;
   for ( int i = 0; i < myFieldInfoArray->Length; i++ )
   {
      // Get the RuntimeFieldHandle of myFieldInfoArray.
      myRuntimeFieldHandle = myFieldInfoArray[ i ]->FieldHandle;

      // Call the GetFieldFromHandle method. 
      FieldInfo^ myFieldInfo = FieldInfo::GetFieldFromHandle( myRuntimeFieldHandle );

      // Display the FieldInfo of myFieldInfo.
      Console::WriteLine( " {0}", myFieldInfo );
   }
}

using System;
using System.Reflection;

public class FieldInfo_GetFieldFromHandle
{
    public string x;
    public char y;
    public float a;
    public int b;

    public static void Main()
    {
        // Get the type of the FieldInfo_GetFieldFromHandle class.
        Type myType = typeof(FieldInfo_GetFieldFromHandle);
        // Get the fields of the FieldInfo_GetFieldFromHandle class.
        FieldInfo [] myFieldInfoArray = myType.GetFields();
        Console.WriteLine("\nThe field information of the declared" +
            " fields x, y, a, and b is:\n");
        RuntimeFieldHandle myRuntimeFieldHandle;
        for(int i = 0; i < myFieldInfoArray.Length; i++)
        {
            // Get the RuntimeFieldHandle of myFieldInfoArray.
            myRuntimeFieldHandle = myFieldInfoArray[i].FieldHandle;
            // Call the GetFieldFromHandle method.
            FieldInfo myFieldInfo = FieldInfo.GetFieldFromHandle(myRuntimeFieldHandle);
            // Display the FieldInfo of myFieldInfo.
            Console.WriteLine("{0}", myFieldInfo);
        }
    }
}

Imports System.Reflection

Public Class FieldInfo_GetFieldFromHandle
    Public x As String
    Public y As Char
    Public a As Single
    Public b As Integer

    Public Shared Sub Main()
        ' Get the type of the FieldInfo_GetFieldFromHandle class.
        Dim myType As Type = GetType(FieldInfo_GetFieldFromHandle)
        ' Get the fields of the FieldInfo_GetFieldFromHandle class.
        Dim myFieldInfoArray As FieldInfo() = myType.GetFields()
        Console.WriteLine(ControlChars.NewLine & _
           "The field information of the declared" & _
           " fields x, y, a, and b is:" & ControlChars.NewLine)
        Dim myRuntimeFieldHandle As RuntimeFieldHandle
        Dim i As Integer
        For i = 0 To myFieldInfoArray.Length - 1
            ' Get the RuntimeFieldHandle of myFieldInfoArray.
            myRuntimeFieldHandle = myFieldInfoArray(i).FieldHandle
            ' Call the GetFieldFromHandle method. 
            Dim myFieldInfo As FieldInfo = FieldInfo.GetFieldFromHandle(myRuntimeFieldHandle)
            ' Display the FieldInfo of myFieldInfo.
            Console.WriteLine("{0}", myFieldInfo)
        Next i
    End Sub
End Class

注解

句柄仅在获取这些句柄的应用程序域中有效。

Source:

FieldInfo.CoreCLR.cs

Source:

FieldInfo.CoreCLR.cs

Source:

FieldInfo.CoreCLR.cs

public:
 static System::Reflection::FieldInfo ^ GetFieldFromHandle(RuntimeFieldHandle handle, RuntimeTypeHandle declaringType);

public static System.Reflection.FieldInfo GetFieldFromHandle (RuntimeFieldHandle handle, RuntimeTypeHandle declaringType);

[System.Runtime.InteropServices.ComVisible(false)]
public static System.Reflection.FieldInfo GetFieldFromHandle (RuntimeFieldHandle handle, RuntimeTypeHandle declaringType);

static member GetFieldFromHandle : RuntimeFieldHandle * RuntimeTypeHandle -> System.Reflection.FieldInfo

[<System.Runtime.InteropServices.ComVisible(false)>]
static member GetFieldFromHandle : RuntimeFieldHandle * RuntimeTypeHandle -> System.Reflection.FieldInfo

Public Shared Function GetFieldFromHandle (handle As RuntimeFieldHandle, declaringType As RuntimeTypeHandle) As FieldInfo

参数

返回

FieldInfo 对象，表示由 handle 指定的字段，该字段的类型为 declaringType 指定的泛型类型。

属性

ComVisibleAttribute

例外

示例

以下示例演示如何检索 FieldInfo 构造的泛型类上的字段的对象。 该示例定义 Visual Basic) Test(Of T) 中的泛型类型 Test<T> (，其类型T为 ，名为 TestField。 该示例获取 RuntimeFieldHandle 的 和 RuntimeTypeHandle （如果 T 为 String），并演示了以下内容：

• 如果使用方法重载， GetFieldFromHandle(RuntimeFieldHandle) 则会引发异常。 即使字段不是 类型 T，也是如此。

• FieldInfo如果运行时类型句柄来自与运行时字段句柄相同的构造，则成功检索 ，在本例Test<string>中为 。

• 如果运行时类型句柄来自兼容构造，则在本例 Test<object>中， FieldInfo 将检索兼容构造上的 字段的 。

• 如果运行时类型句柄不是来自兼容的构造，则会引发异常。 在这种情况下，为 T指定了值类型。

using System;
using System.Reflection;

// A generic class with a field whose type is specified by the
// generic type parameter of the class.
public class Test<T>
{
    public T TestField;
}

public class Example
{
    public static void Main()
    {
        // Get type handles for Test<String> and its field.
        RuntimeTypeHandle rth = typeof(Test<string>).TypeHandle;
        RuntimeFieldHandle rfh = typeof(Test<string>).GetField("TestField").FieldHandle;

        // When a field belongs to a constructed generic type,
        // such as Test<String>, retrieving the field from the
        // field handle requires the type handle of the constructed
        // generic type. An exception is thrown if the type is not
        // included.
        try
        {
            FieldInfo f1 = FieldInfo.GetFieldFromHandle(rfh);
        }
        catch(Exception ex)
        {
            Console.WriteLine("{0}: {1}", ex.GetType().Name, ex.Message);
        }

        // To get the FieldInfo for a field on a generic type, use the
        // overload that specifies the type handle.
        FieldInfo fi = FieldInfo.GetFieldFromHandle(rfh, rth);
        Console.WriteLine("\r\nThe type of {0} is: {1}", fi.Name, fi.FieldType);

        // All constructions of Test<T> for which T is a reference
        // type share the same implementation, so the same runtime
        // field handle can be used to retrieve the FieldInfo for
        // TestField on any such construction. Here the runtime field
        // handle is used with Test<Object>.
        fi = FieldInfo.GetFieldFromHandle(rfh, typeof(Test<object>).TypeHandle);
        Console.WriteLine("\r\nThe type of {0} is: {1}", fi.Name, fi.FieldType);

        // Each construction of Test<T> for which T is a value type
        // has its own unique implementation, and an exception is thrown
        // if you supply a constructed type other than the one that
        // the runtime field handle belongs to.
        try
        {
            fi = FieldInfo.GetFieldFromHandle(rfh, typeof(Test<int>).TypeHandle);
        }
        catch(Exception ex)
        {
            Console.WriteLine("\r\n{0}: {1}", ex.GetType().Name, ex.Message);
        }
    }
}

/* This code example produces output similar to the following:

ArgumentException: Cannot resolve field TestField because the declaring type of
the field handle Test`1[T] is generic. Explicitly provide the declaring type to
GetFieldFromHandle.

The type of TestField is: System.String

The type of TestField is: System.Object

ArgumentException: Type handle 'Test`1[System.Int32]' and field handle with decl
aring type 'Test`1[System.__Canon]' are incompatible. Get RuntimeFieldHandle and
 declaring RuntimeTypeHandle off the same FieldInfo.
 */

Imports System.Reflection

' A generic class with a field whose type is specified by the 
' generic type parameter of the class.
Public Class Test(Of T)
    Public TestField As T 
End Class

Public Class Example

    Public Shared Sub Main()

        ' Get type handles for Test(Of String) and its field.
        Dim rth As RuntimeTypeHandle = _
            GetType(Test(Of String)).TypeHandle
        Dim rfh As RuntimeFieldHandle = _
            GetType(Test(Of String)).GetField("TestField").FieldHandle

        ' When a field belongs to a constructed generic type, 
        ' such as Test(Of String), retrieving the field from the
        ' field handle requires the type handle of the constructed
        ' generic type. An exception is thrown if the type is not
        ' included.
        Try
            Dim f1 As FieldInfo = FieldInfo.GetFieldFromHandle(rfh)
        Catch ex As Exception
            Console.WriteLine("{0}: {1}", ex.GetType().Name, ex.Message)
        End Try

        ' To get the FieldInfo for a field on a generic type, use the
        ' overload that specifies the type handle.
        Dim fi As FieldInfo = FieldInfo.GetFieldFromHandle(rfh, rth)
        Console.WriteLine(vbCrLf & "The type of {0} is: {1}", _
            fi.Name, fi.FieldType)

        ' All constructions of Test(Of T) for which T is a reference
        ' type share the same implementation, so the same runtime 
        ' field handle can be used to retrieve the FieldInfo for 
        ' TestField on any such construction. Here the runtime field
        ' handle is used with Test(Of Object).
        fi = FieldInfo.GetFieldFromHandle(rfh, _
                               GetType(Test(Of Object)).TypeHandle)
        Console.WriteLine(vbCrLf & "The type of {0} is: {1}", _
            fi.Name, fi.FieldType)

        ' Each construction of Test(Of T) for which T is a value type
        ' has its own unique implementation, and an exception is thrown
        ' if you supply a constructed type other than the one that 
        ' the runtime field handle belongs to.  
        Try
            fi = FieldInfo.GetFieldFromHandle(rfh, _
                               GetType(Test(Of Integer)).TypeHandle)
        Catch ex As Exception
            Console.WriteLine(vbCrLf & "{0}: {1}", ex.GetType().Name, ex.Message)
        End Try

    End Sub
End Class

' This code example produces output similar to the following:
'
'ArgumentException: Cannot resolve field TestField because the declaring type of
'the field handle Test`1[T] is generic. Explicitly provide the declaring type to
'GetFieldFromHandle.
'
'The type of TestField is: System.String
'
'The type of TestField is: System.Object
'
'ArgumentException: Type handle 'Test`1[System.Int32]' and field handle with decl
'aring type 'Test`1[System.__Canon]' are incompatible. Get RuntimeFieldHandle and
' declaring RuntimeTypeHandle off the same FieldInfo.

注解

句柄仅在获取这些句柄的应用程序域中有效。

建议的做法是， declaringType 应始终是属于的构造类型的运行时类型 handle 句柄。 也就是说，如果 handle 是属于 Visual Basic) 中 (MyType(Of Integer) 的字段的运行时字段MyType<int>句柄，declaringType则 为 的MyType<int>运行时类型句柄。 请勿使用泛型类型定义的运行时类型句柄，除非运行时字段句柄表示泛型类型定义上的字段。

在某些情况下，实现是兼容的。 例如，单个实现由使用泛型类型参数的引用类型从特定泛型类型定义构造的所有类型共享。 例如， MyType<string>、 MyType<object>和 MyType<ArrayList> 都共享相同的实现。 在这种情况下， FieldInfo 返回的对象表示类型 declaringType 上的字段，该字段指定，而不考虑 的原始源 handle。 不建议这样做，因为它仅在构造类型的泛型类型参数是引用类型时才有效。

如果泛型参数是值类型，则构造类型的运行时类型句柄与引用类型位于同一泛型参数位置或该位置中具有不同值类型的构造中的运行时字段句柄不兼容。 在这种情况下，使用 FieldInfo.GetFieldFromHandle(RuntimeFieldHandle, RuntimeTypeHandle) 重载的唯一方法是确保 declaringType 是属于的已构造类型的运行时类型 handle 句柄。