无法获取PropertyInfo SetValue以用于结构 [英] Cannot get PropertyInfo SetValue to Work for a Structure
问题描述
我已经从PropertyInfo的MSDN帮助中调整了以下代码
SetValue。在原始代码中，结构MyStructure被定义为
类MyProperty，并且它按预期工作。我已经注释了
类Mypropertyinfo的微小变化。
但是，当使用结构时，第二次调用GetValue会返回
"默认标题。谁能告诉我为什么，以及如何使这项工作？
< code>
进口系统
进口系统.Reflection
公共结构MyStructure
私人myCaption字符串
公共财产标题（）作为String
获取
返回myCaption
结束获取
设置（ByVal Value As String）
如果myCaption<>价值然后
myCaption =价值
结束如果
结束套件
结束物业
结束结构
类Mypropertyinfo
公共共享功能Main（）为整数
控制台.WriteLine（Reflection.PropertyInfo）
''''昏暗的af新的MyProperty''原版
昏暗af作为MyStructure
af.Caption ="默认标题"
''获取类型和PropertyInfo
Dim MyType As Type = af .GetType
Dim Mypropertyinfo As PropertyInfo = MyType.GetProperty（" Caption"）
''获取并显示GetValue方法
Console.WriteLine（" GetValue - "& Mypropertyinfo.GetValue（af，
Nothing）.ToString（））
''使用更改标题的SetValue方法
Mypropertyinfo.SetValue（af，此标题已更改。，
Nothin g）
''再次获取标题并显示它
Console.WriteLine（" GetValue - " &安培; Mypropertyinfo.GetValue（af，
没什么）.ToString（））
Console.ReadLine（）
返回0
结束功能
结束课程
< / code>
TIA
Charles
I have adapted the following code from the MSDN help for PropertyInfo
SetValue. In the original code, the structure MyStructure is defined as a
class MyProperty, and it works as expected. There is also a minor change in
class Mypropertyinfo, which I have commented out.
When using a structure, however, the second call to GetValue returns
"Default caption". Can anyone tell me why, and how I can make this work?
<code>
Imports System
Imports System.Reflection
Public Structure MyStructure
Private myCaption As String
Public Property Caption() As String
Get
Return myCaption
End Get
Set(ByVal Value As String)
If myCaption <> Value Then
myCaption = Value
End If
End Set
End Property
End Structure
Class Mypropertyinfo
Public Shared Function Main() As Integer
Console.WriteLine("Reflection.PropertyInfo")
''''Dim af As New MyProperty '' original
Dim af As MyStructure
af.Caption = "Default caption"
'' Get the type and PropertyInfo
Dim MyType As Type = af.GetType
Dim Mypropertyinfo As PropertyInfo = MyType.GetProperty("Caption")
'' Get and display the GetValue method
Console.WriteLine("GetValue - " & Mypropertyinfo.GetValue(af,
Nothing).ToString())
'' Use the SetValue method to change the caption
Mypropertyinfo.SetValue(af, "This caption has been changed.",
Nothing)
'' Get the caption again and display it
Console.WriteLine("GetValue - " & Mypropertyinfo.GetValue(af,
Nothing).ToString())
Console.ReadLine()
Return 0
End Function
End Class
</code>
TIA
Charles
推荐答案
这是因为结构是一种值类型，同时包含SetValue和GetValue
expect对象导致参数被装箱。因此，GetValue和
SetValue正在处理盒装对象而不是实际结构。我相信这种技术不会对结构起作用 - 虽然我可能错了。
希望有帮助......
Imran。
" Charles Law" < BL *** @ nowhere.com>在消息中写道
news：et ************* @ TK2MSFTNGP11.phx.gbl ...
This is because a structure is a value type and both SetValue and GetValue
expect Objects causing the arguments to boxed. As a result, the GetValue and
SetValue are working the boxed object rather than on the actual structure. I
believe this technique won''t work on structures - I could be wrong though.
hope that helps..
Imran.
"Charles Law" <bl***@nowhere.com> wrote in message
news:et*************@TK2MSFTNGP11.phx.gbl...
我改编了以下代码来自PropertyInfo的MSDN帮助
SetValue。在原始代码中，结构MyStructure被定义为一个类MyProperty，它按预期工作。在Mypropertyinfo类中还有一个小的变化
，我已经注释掉了。
当使用结构时，第二次调用GetValue会返回
默认标题。 。任何人都可以告诉我为什么，以及我如何使这项工作？
< code>
进口系统
进口System.Reflection
公共结构MyStructure
私人myCaption为字符串
公共属性标题（）为字符串
获取
返回myCaption
结束获取
设置（ByVal Value As String）
如果myCaption<>价值然后
myCaption =价值
结束如果
结束设置
结束属性
结束结构
类Mypropertyinfo
公共共享功能Main（）作为整数
Console.WriteLine（" Reflection.PropertyInfo"）
''''昏暗af作为新MyProperty''原创
af.Caption ="默认标题
''获取类型和PropertyInfo
Dim MyType As Type = af.GetType
Dim Mypropertyinfo As PropertyInfo = MyType.GetProperty（Caption）
''获取并显示GetValue方法
Console.WriteLine（" GetValue - "& Mypropertyinfo.GetValue（af，
Nothing）.ToString（））
''使用SetValue方法更改标题
Mypropertyinfo.SetValue（af，此标题有陈ged。"，
没什么。
''再次获取标题并显示它
Console.WriteLine（" GetValue - " &安培; Mypropertyinfo.GetValue（af，
没什么）.ToString（））
Console.ReadLine（）
返回0
结束功能
结束班
< / code>
TIA
I have adapted the following code from the MSDN help for PropertyInfo
SetValue. In the original code, the structure MyStructure is defined as a
class MyProperty, and it works as expected. There is also a minor change in class Mypropertyinfo, which I have commented out.
When using a structure, however, the second call to GetValue returns
"Default caption". Can anyone tell me why, and how I can make this work?
<code>
Imports System
Imports System.Reflection
Public Structure MyStructure
Private myCaption As String
Public Property Caption() As String
Get
Return myCaption
End Get
Set(ByVal Value As String)
If myCaption <> Value Then
myCaption = Value
End If
End Set
End Property
End Structure
Class Mypropertyinfo
Public Shared Function Main() As Integer
Console.WriteLine("Reflection.PropertyInfo")
''''Dim af As New MyProperty '' original
Dim af As MyStructure
af.Caption = "Default caption"
'' Get the type and PropertyInfo
Dim MyType As Type = af.GetType
Dim Mypropertyinfo As PropertyInfo = MyType.GetProperty("Caption")
'' Get and display the GetValue method
Console.WriteLine("GetValue - " & Mypropertyinfo.GetValue(af,
Nothing).ToString())
'' Use the SetValue method to change the caption
Mypropertyinfo.SetValue(af, "This caption has been changed.",
Nothing)
'' Get the caption again and display it
Console.WriteLine("GetValue - " & Mypropertyinfo.GetValue(af,
Nothing).ToString())
Console.ReadLine()
Return 0
End Function
End Class
</code>
TIA
Charles
您好伊姆兰
感谢您的快速回复。它确实有道理，但遗憾的是，如果它是真的，我有点卡住了，因为我需要能够使用这个或类似的技术来设置
物业价值。
您或其他任何人知道某种解决方法或其他方式吗？
Charles
" Imran Koradia" <无**** @ microsoft.com>在消息中写道
新闻：OE ************** @ TK2MSFTNGP10.phx.gbl ...
Hi Imran
Thanks for a quick response. It does make sense, but sadly, if it is true, I
am a bit stuck, as I need to be able to use this or a similar technique to
set property values.
Do you, or anyone else know of a workaround, or another way of doing it?
Charles
"Imran Koradia" <no****@microsoft.com> wrote in message
news:OE**************@TK2MSFTNGP10.phx.gbl...
这是因为一个结构是一个值类型，SetValue和GetValue都希望对象导致参数被装箱。因此，GetValue
和SetValue正在处理盒装对象而不是实际结构。
我相信这种技术不适用于结构 - 我可以虽然错了。
希望有所帮助..
伊姆兰。
查尔斯劳 < BL *** @ nowhere.com>在消息中写道
新闻：et ************* @ TK2MSFTNGP11.phx.gbl ...
This is because a structure is a value type and both SetValue and GetValue
expect Objects causing the arguments to boxed. As a result, the GetValue
and
SetValue are working the boxed object rather than on the actual structure.
I
believe this technique won''t work on structures - I could be wrong though.
hope that helps..
Imran.
"Charles Law" <bl***@nowhere.com> wrote in message
news:et*************@TK2MSFTNGP11.phx.gbl...
我已经从MSDN帮助改编了以下代码对于PropertyInfo
SetValue。在原始代码中，结构MyStructure被定义为一个类MyProperty，它按预期工作。在
I have adapted the following code from the MSDN help for PropertyInfo
SetValue. In the original code, the structure MyStructure is defined as a
class MyProperty, and it works as expected. There is also a minor change
类Mypropertyinfo中也有一个小的改动
in
我已经注释掉了。
当使用结构时，第二次调用GetValue返回
默认标题。任何人都可以告诉我为什么，以及我如何使这项工作？
< code>
进口系统
进口System.Reflection
公共结构MyStructure
私人myCaption为字符串
公共属性标题（）为字符串
获取
返回myCaption
结束获取
设置（ByVal Value As String）
如果myCaption<>价值然后
myCaption =价值
结束如果
结束设置
结束属性
结束结构
类Mypropertyinfo
公共共享功能Main（）作为整数
Console.WriteLine（" Reflection.PropertyInfo"）
''''昏暗af作为新MyProperty''原创
af.Caption ="默认标题
''获取类型和PropertyInfo
Dim MyType As Type = af.GetType
Dim Mypropertyinfo As PropertyInfo =
MyType.GetProperty（Caption）
''获取并显示GetValue方法
Console.WriteLine（" GetValue - && Mypropertyinfo.GetValue（af，
Nothing）.ToString（））
''使用SetValue方法更改标题
Mypropertyinfo.SetValue（af，& ;这个标题有蜜蜂n改了。，没什么。
''再次获取标题并显示它
Console.WriteLine（" GetValue - " &安培; Mypropertyinfo.GetValue（af，
没什么）.ToString（））
Console.ReadLine（）
返回0
结束功能
结束班
< / code>
TIA
class Mypropertyinfo, which I have commented out.
When using a structure, however, the second call to GetValue returns
"Default caption". Can anyone tell me why, and how I can make this work?
<code>
Imports System
Imports System.Reflection
Public Structure MyStructure
Private myCaption As String
Public Property Caption() As String
Get
Return myCaption
End Get
Set(ByVal Value As String)
If myCaption <> Value Then
myCaption = Value
End If
End Set
End Property
End Structure
Class Mypropertyinfo
Public Shared Function Main() As Integer
Console.WriteLine("Reflection.PropertyInfo")
''''Dim af As New MyProperty '' original
Dim af As MyStructure
af.Caption = "Default caption"
'' Get the type and PropertyInfo
Dim MyType As Type = af.GetType
Dim Mypropertyinfo As PropertyInfo =
MyType.GetProperty("Caption")
'' Get and display the GetValue method
Console.WriteLine("GetValue - " & Mypropertyinfo.GetValue(af,
Nothing).ToString())
'' Use the SetValue method to change the caption
Mypropertyinfo.SetValue(af, "This caption has been changed.",
Nothing)
'' Get the caption again and display it
Console.WriteLine("GetValue - " & Mypropertyinfo.GetValue(af,
Nothing).ToString())
Console.ReadLine()
Return 0
End Function
End Class
</code>
TIA
Charles
Charles，
最简单的方法是不使用结构。
否则我相信你需要使用C＃，因为VB.NET添加了对
RuntimeHelpers.GetObjectValue的调用每当你尝试用
对象变量做某事时。
问题使用Structure是一个结构是一个值类型，因此调用GetObjectValue，其中包装了一个值类型。 GetObjectValue
用于确保当您在对象变量中指定值类型
另一个对象变量时，会生成该值的副本，而不是对<的引用br />
相同的实例。这与类型化值类型的工作方式保持一致。
您可以使用ILDASM.EXE查看VB.NET何时添加调用
RuntimeHelpers.GetObjectValue。
我建议您尝试使用CallByName，但是它似乎首先调用
RuntimeHelpers.GetObjectValue ...
希望这有帮助
Jay
" Charles Law" < BL *** @ nowhere.com>在消息中写道
新闻：％2 **************** @ TK2MSFTNGP10.phx.gbl ...
Charles,
The "easiest" way would be not to use a Structure.
Otherwise I believe you will need to use C#, as VB.NET adds calls to a
RuntimeHelpers.GetObjectValue whenever you try to do something with an
object variable.
The "problem" with using a Structure is that a Structure is a value type,
hence the call to GetObjectValue which "boxes a value type". GetObjectValue
is used to ensure that when you assign a value type in an object variable to
another object variable a copy of the value is made, not a reference to the
same instance. Which is in keeping with how typed value types work.
You can use ILDASM.EXE to see when VB.NET adds calls to
RuntimeHelpers.GetObjectValue.
I would suggest you try CallByName, however it appears to call
RuntimeHelpers.GetObjectValue first also...
Hope this helps
Jay
"Charles Law" <bl***@nowhere.com> wrote in message
news:%2****************@TK2MSFTNGP10.phx.gbl...
Hi Imran
感谢您的快速回复。它确实有意义，但遗憾的是，如果它是真的，
我有点卡住了，因为我需要能够使用这个或类似的技术来设置属性值。
<你或其他任何人都知道一种解决方法或其他方式吗？
Charles
Imran Koradia <无**** @ microsoft.com>在消息中写道
新闻：OE ************** @ TK2MSFTNGP10.phx.gbl ...
Hi Imran
Thanks for a quick response. It does make sense, but sadly, if it is true,
I am a bit stuck, as I need to be able to use this or a similar technique
to set property values.
Do you, or anyone else know of a workaround, or another way of doing it?
Charles
"Imran Koradia" <no****@microsoft.com> wrote in message
news:OE**************@TK2MSFTNGP10.phx.gbl...
这是因为结构是值类型并且SetValue和
GetValue
期望对象导致参数被装箱。因此，GetValue
和SetValue正在处理盒装对象而不是实际的结构。我相信这种技术不会对结构起作用 - 我可能错了。
希望有所帮助..
Imran。
<查尔斯·劳斯（Charles Law） < BL *** @ nowhere.com>在消息中写道
新闻：et ************* @ TK2MSFTNGP11.phx.gbl ...
This is because a structure is a value type and both SetValue and
GetValue
expect Objects causing the arguments to boxed. As a result, the GetValue
and
SetValue are working the boxed object rather than on the actual
structure. I
believe this technique won''t work on structures - I could be wrong
though.
hope that helps..
Imran.
"Charles Law" <bl***@nowhere.com> wrote in message
news:et*************@TK2MSFTNGP11.phx.gbl...
我已经从MSDN帮助改编了以下代码对于PropertyInfo
SetValue。在原始代码中，结构MyStructure被定义为类MyProperty，它按预期工作。在
I have adapted the following code from the MSDN help for PropertyInfo
SetValue. In the original code, the structure MyStructure is defined as
a
class MyProperty, and it works as expected. There is also a minor change
类Mypropertyinfo中也有一个小的改动
in
我已经注释掉了。
当使用结构时，第二次调用GetValue返回
默认标题。任何人都可以告诉我为什么，以及我如何使这项工作？
< code>
进口系统
进口System.Reflection
公共结构MyStructure
私人myCaption为字符串
公共属性标题（）为字符串
获取
返回myCaption
结束获取
设置（ByVal Value As String）
如果myCaption<>价值然后
myCaption =价值
结束如果
结束设置
结束属性
结束结构
类Mypropertyinfo
公共共享功能Main（）作为整数
Console.WriteLine（" Reflection.PropertyInfo"）
''''昏暗af作为新MyProperty''原创
af.Caption ="默认标题
''获取类型和PropertyInfo
Dim MyType As Type = af.GetType
Dim Mypropertyinfo As PropertyInfo =
MyType.GetProperty（Caption）
''获取并显示GetValue方法
Console.WriteLine（" GetValue - && Mypropertyinfo.GetValue（af，
Nothing）.ToString（））
''使用SetValue方法更改标题
Mypropertyinfo.SetValue（af，& ;这个标题有蜜蜂n改了。，没什么。
''再次获取标题并显示它
Console.WriteLine（" GetValue - " &安培; Mypropertyinfo.GetValue（af，
没什么）.ToString（））
Console.ReadLine（）
返回0
结束功能
结束班
< / code>
TIA
class Mypropertyinfo, which I have commented out.
When using a structure, however, the second call to GetValue returns
"Default caption". Can anyone tell me why, and how I can make this work?
<code>
Imports System
Imports System.Reflection
Public Structure MyStructure
Private myCaption As String
Public Property Caption() As String
Get
Return myCaption
End Get
Set(ByVal Value As String)
If myCaption <> Value Then
myCaption = Value
End If
End Set
End Property
End Structure
Class Mypropertyinfo
Public Shared Function Main() As Integer
Console.WriteLine("Reflection.PropertyInfo")
''''Dim af As New MyProperty '' original
Dim af As MyStructure
af.Caption = "Default caption"
'' Get the type and PropertyInfo
Dim MyType As Type = af.GetType
Dim Mypropertyinfo As PropertyInfo =
MyType.GetProperty("Caption")
'' Get and display the GetValue method
Console.WriteLine("GetValue - " & Mypropertyinfo.GetValue(af,
Nothing).ToString())
'' Use the SetValue method to change the caption
Mypropertyinfo.SetValue(af, "This caption has been changed.",
Nothing)
'' Get the caption again and display it
Console.WriteLine("GetValue - " & Mypropertyinfo.GetValue(af,
Nothing).ToString())
Console.ReadLine()
Return 0
End Function
End Class
</code>
TIA
Charles
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