473,320 Members | 1,933 Online
Bytes | Software Development & Data Engineering Community
Post Job

Home Posts Topics Members FAQ

Join Bytes to post your question to a community of 473,320 software developers and data experts.

A Reflection Puzzle:(

HI, all,
I just want to invoke an internal method named 'ResolveClientUrl', which
is defined in class System.Web.UI.Control, using an instance object of a
type that derives from Control.

Let's see the following code snippet (class MyControl is a sub class that
derives directly from System.Web.UI.Control):
//...
MyControl instance = new MyControl();
Type type = instance.GetType();
object[] args = new object[] {"images/test.gif"};
string path = (string)type.InvokeMember("ResolveClientUrl",
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance |
BindingFlags.GetProperty,
null, instance, args);
//...

Actually, I intended to use the type object of MyControl to invoke the inherited
method 'ResolveClientUrl', but an Exception occured, described as "Method
LaserWeb.Presentation.MyControl.ResolveClientUrl not found." It seems that
reflection didn't search in the inherited members up the class hierarchy,
since 'ResolveClientUrl' is a declared method in the base class Control.

This action, I guess, should only be taken when BindingFlags.DeclaredOnly
is specified for invoking a method, otherwise inherited members derived from
base class should be considered. However, in this sample code, it didn't
work:( I did not pass the BindingFlags.DeclaredOnly flag. Then why? How could
it happen? I was puzzled:( Help!

Regards,
Laser Lu
Nov 17 '05 #1
6 1450
Laser Lu <la******@hotmail.com> wrote:
HI, all,
I just want to invoke an internal method named 'ResolveClientUrl', which
is defined in class System.Web.UI.Control, using an instance object of a
type that derives from Control.

Let's see the following code snippet (class MyControl is a sub class that
derives directly from System.Web.UI.Control):
//...
MyControl instance = new MyControl();
Type type = instance.GetType();
object[] args = new object[] {"images/test.gif"};
string path = (string)type.InvokeMember("ResolveClientUrl",
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance |
BindingFlags.GetProperty,
null, instance, args);
//...

Actually, I intended to use the type object of MyControl to invoke the inherited
method 'ResolveClientUrl', but an Exception occured, described as "Method
LaserWeb.Presentation.MyControl.ResolveClientUrl not found." It seems that
reflection didn't search in the inherited members up the class hierarchy,
since 'ResolveClientUrl' is a declared method in the base class Control.

This action, I guess, should only be taken when BindingFlags.DeclaredOnly
is specified for invoking a method, otherwise inherited members derived from
base class should be considered. However, in this sample code, it didn't
work:( I did not pass the BindingFlags.DeclaredOnly flag. Then why? How could
it happen? I was puzzled:( Help!


Even if you could find the member, you shouldn't be able to invoke it,
if it's internal to a separate assembly.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Nov 17 '05 #2
Hello Jon Skeet, actually, the following code runs well:
//...
MyControl instance = new MyControl();
Type type = typeof(System.Web.UI.Control); // here use the Type object of
Control, not of MyControl.
object[] args = new object[] {"images/test.gif"};
string path = (string)type.InvokeMember("ResolveClientUrl",
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance
| BindingFlags.GetProperty,
null, instance, args);
//...

The only change, that I've made on the code, is that I used the Type object
of Control instead. And the Control class is the declaring type of the member
'ResolveClientUrl'.

Maybe I didn't understand what do you mean in your post. However, the above
code runs well without any exceptions, and the method member gets invoked
correctly, even it is internal to my assembly.

Still, My puzzle is how to invoke inherited members using derived types?
It seems that there's no difference in cases whether you have a BindingFlags.DeclareOnly
specified or not:( Why is it so strange?
Laser Lu <la******@hotmail.com> wrote:
HI, all,
I just want to invoke an internal method named 'ResolveClientUrl',
which
is defined in class System.Web.UI.Control, using an instance object
of a
type that derives from Control.
Let's see the following code snippet (class MyControl is a sub class
that
derives directly from System.Web.UI.Control):
//...
MyControl instance = new MyControl();
Type type = instance.GetType();
object[] args = new object[] {"images/test.gif"};
string path = (string)type.InvokeMember("ResolveClientUrl",
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance
|
BindingFlags.GetProperty,
null, instance, args);
//...
Actually, I intended to use the type object of MyControl to invoke
the inherited method 'ResolveClientUrl', but an Exception occured,
described as "Method LaserWeb.Presentation.MyControl.ResolveClientUrl
not found." It seems that reflection didn't search in the inherited
members up the class hierarchy, since 'ResolveClientUrl' is a
declared method in the base class Control.

This action, I guess, should only be taken when
BindingFlags.DeclaredOnly is specified for invoking a method,
otherwise inherited members derived from base class should be
considered. However, in this sample code, it didn't work:( I did not
pass the BindingFlags.DeclaredOnly flag. Then why? How could it
happen? I was puzzled:( Help!

Even if you could find the member, you shouldn't be able to invoke it,
if it's internal to a separate assembly.


Nov 17 '05 #3
Laser Lu <la******@hotmail.com> wrote:
Hello Jon Skeet, actually, the following code runs well:
//...
MyControl instance = new MyControl();
Type type = typeof(System.Web.UI.Control); // here use the Type object of
Control, not of MyControl.
object[] args = new object[] {"images/test.gif"};
string path = (string)type.InvokeMember("ResolveClientUrl",
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance
| BindingFlags.GetProperty,
null, instance, args);
//...

The only change, that I've made on the code, is that I used the Type object
of Control instead. And the Control class is the declaring type of the member
'ResolveClientUrl'.

Maybe I didn't understand what do you mean in your post. However, the above
code runs well without any exceptions, and the method member gets invoked
correctly, even it is internal to my assembly.
It may in some trust environments, but:

a) It won't in others
b) There's no guarantee that that method will be in future versions of
the framework
c) Internal methods should *not* be seen as part of the public
interface which you should call. If they were meant to be called by the
"outside world", they'd have been made protected or public.
Still, My puzzle is how to invoke inherited members using derived
types? It seems that there's no difference in cases whether you have
a BindingFlags.DeclareOnly specified or not:( Why is it so strange?


Well, just looking at your code again, you're using
BindingFlags.GetProperty, which probably isn't what you're after for a
method call.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Nov 17 '05 #4
Jon Skeet wrote:
Well, just looking at your code again, you're using
BindingFlags.GetProperty, which probably isn't what you're after for a
method call.

So sorry for the mistake I made during copying code to this post!! The original
code snippet should be:
//...
MyControl instance = new MyControl();
Type type = instance.GetType();
object[] args = new object[] {"images/test.gif"};
string path = (string)type.InvokeMember("ResolveClientUrl",
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance
| BindingFlags.InvokeMethod,
null, instance, args); // Exception is thrown, withou no such member
found in the derived class.
//...

The reason why I made this mistake is actually I've wrote a helper class
as the following:
// code starts
using System;
using System.Reflection;

namespace LaserWeb.Presentation.Common
{
internal sealed class Reflector
{
private Reflector() {}

public static object GetProperty(object instance, string name)
{
Type type = instance.GetType();
return type.InvokeMember(name,
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance
| BindingFlags.GetProperty,
null, instance, null);
}

public static object GetProperty(Type type, object instance, string name)
{
return type.InvokeMember(name,
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance
| BindingFlags.GetProperty,
null, instance, null);
}

public static object InvokeMethod(object instance, string name, object[]
args)
{
Type type = instance.GetType();
return type.InvokeMember(name,
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance
| BindingFlags.InvokeMethod,
null, instance, args);
}

public static object InvokeMethod(Type type, object instance, string name,
object[] args)
{
return type.InvokeMember(name,
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance
| BindingFlags.InvokeMethod,
null, instance, args);
}
}
}
// code ends
When I posted the puzzle, the original code snippet is not handy (I have
removed it from my project), so I made the wrong code snippet by copying
the code fragment from Reflector.GetProperty() and modifing base on that
code. That's the reason why I made the mistake, sorry again for misleading
all of you in your reading!

If you use the above helper class as the following, you will still find the
problem I described:
// ..
MyControl instance = new MyControl();
object args = new objet[] {"images/test.gif"};
Reflector.InvokeMethod(typeof(System.Web.UI.Contro l), instance, "ResolveClientUrl",
args); // This will works fine.
Reflector.InvokeMethod(instance, "ResolveClientUrl", args); // An exception
will be thrown here, indicating member not found.
// ...

I don't know why I had encountered such a strange problem, and got puzzled.
You may make the similar sample code and have a try, to see whether what
I said would happen. Thanks:)

Laser Lu.
Nov 17 '05 #5
Laser Lu <la******@hotmail.com> wrote:
Jon Skeet wrote:
Well, just looking at your code again, you're using
BindingFlags.GetProperty, which probably isn't what you're after for a
method call.

So sorry for the mistake I made during copying code to this post!! The original
code snippet should be:
//...
MyControl instance = new MyControl();
Type type = instance.GetType();
object[] args = new object[] {"images/test.gif"};
string path = (string)type.InvokeMember("ResolveClientUrl",
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance
| BindingFlags.InvokeMethod,
null, instance, args); // Exception is thrown, withou no such member
found in the derived class.
//...


<snip>

Okay, well I can reproduce the problem, but not solve it. However, as
I've said before, this isn't something you should be doing anyway. I
urge you to change your design so that you don't need to call internal
methods in other assemblies.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Nov 17 '05 #6
Okay, thank you very much!
And I will try to avoid invoking internal or private members in ther future,
as doing this will certainly violate the design principles:)

Okay, well I can reproduce the problem, but not solve it. However, as
I've said before, this isn't something you should be doing anyway. I
urge you to change your design so that you don't need to call internal
methods in other assemblies.


Nov 17 '05 #7

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

6
by: Laser Lu | last post by:
HI, all, I just want to invoke an internal method named 'ResolveClientUrl', which is defined in class System.Web.UI.Control, using an instance object of a type that derives from Control. Let's...
6
by: Laser Lu | last post by:
HI, all, I just want to invoke an internal method named 'ResolveClientUrl', which is defined in class System.Web.UI.Control, using an instance object of a type that derives from Control. Let's...
1
by: xavier vazquez | last post by:
I have a problem with a program that does not working properly...when the program run is suppose to generate a cross word puzzle , when the outcome show the letter of the words overlap one intop of...
4
by: honey777 | last post by:
Problem: 15 Puzzle This is a common puzzle with a 4x4 playing space with 15 tiles, numbered 1 through 15. One "spot" is always left blank. Here is an example of the puzzle: The goal is to...
0
by: DolphinDB | last post by:
The formulas of 101 quantitative trading alphas used by WorldQuant were presented in the paper 101 Formulaic Alphas. However, some formulas are complex, leading to challenges in calculation. Take...
0
by: ryjfgjl | last post by:
ExcelToDatabase: batch import excel into database automatically...
1
isladogs
by: isladogs | last post by:
The next Access Europe meeting will be on Wednesday 6 Mar 2024 starting at 18:00 UK time (6PM UTC) and finishing at about 19:15 (7.15PM). In this month's session, we are pleased to welcome back...
0
by: Vimpel783 | last post by:
Hello! Guys, I found this code on the Internet, but I need to modify it a little. It works well, the problem is this: Data is sent from only one cell, in this case B5, but it is necessary that data...
0
by: ArrayDB | last post by:
The error message I've encountered is; ERROR:root:Error generating model response: exception: access violation writing 0x0000000000005140, which seems to be indicative of an access violation...
0
by: CloudSolutions | last post by:
Introduction: For many beginners and individual users, requiring a credit card and email registration may pose a barrier when starting to use cloud servers. However, some cloud server providers now...
0
by: Defcon1945 | last post by:
I'm trying to learn Python using Pycharm but import shutil doesn't work
0
by: af34tf | last post by:
Hi Guys, I have a domain whose name is BytesLimited.com, and I want to sell it. Does anyone know about platforms that allow me to list my domain in auction for free. Thank you
0
by: Faith0G | last post by:
I am starting a new it consulting business and it's been a while since I setup a new website. Is wordpress still the best web based software for hosting a 5 page website? The webpages will be...

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.