Reflection: How to discover name of a property at run time.

[=?Utf-8?B?VmljdG9y?=]

Is it a way to discover, at the run time, the name of a property of an object?
In other words is it possible to create a method GetPropertyName , that takes
a property of an object and returns the name of that property? So:

string name = GetPropertyName (int.MaxValue); // returns “MaxValue”
string name = GetPropertyName (DateTime.Now); // returns “Now”

(Something similar exists to
System.Reflecti on.MethodInfo.G etCurrentMethod ().Name; that returns the name
of the current method)

[Peter Duniho]

Re: Reflection: How to discover name of a property at run time.

On Sat, 16 Aug 2008 21:23:00 -0700, Victor
<Victor@discuss ions.microsoft. comwrote:

Is it a way to discover, at the run time, the name of a property of an
object?
In other words is it possible to create a method GetPropertyName , that
takes
a property of an object and returns the name of that property? So:
>
string name = GetPropertyName (int.MaxValue); // returns “MaxValue”
string name = GetPropertyName (DateTime.Now); // returns “Now”
>
(Something similar exists to
System.Reflecti on.MethodInfo.G etCurrentMethod ().Name; that returns the
name
of the current method)

MethodInfo.GetC urrentMethod() is only useful when called from _within_ the
method in question. That's completely different from the example lines of
code you posted, so it's very difficult to understand exactly what you
want to do.

That said, if you are writing code that is in the getter or setter of a
property, you can still use the MethodInfo.GetC urrentMethod() method. The
name of the property is embedded in the names of the getter and setter
methods, since those names are just the name of the property with the text
"get_" and "set_" prepended.

If that doesn't provide what you want, I think you should try to rephrase
your question so that it's more clear.

Pete

[Duggi]

Re: Reflection: How to discover name of a property at run time.

On Aug 17, 9:23 am, Victor <Vic...@discuss ions.microsoft. comwrote:

Is it a way to discover, at the run time, the name of a property of an object?
In other words is it possible to create a method GetPropertyName , that takes
a property of an object and returns the name of that property? So:
>
string name = GetPropertyName (int.MaxValue); // returns “MaxValue”
string name = GetPropertyName (DateTime.Now); // returns “Now”
>
(Something similar exists to
System.Reflecti on.MethodInfo.G etCurrentMethod ().Name; that returns the name
of the current method)

Try the following snippet of code..

Type myType = tc.GetType();
PropertyInfo[] allPropertiesIn fo = myType.GetPrope rties();

foreach (PropertyInfo pInfo in allPropertiesIn fo)
{
Console.WriteLi ne(((System.Ref lection.MemberI nfo)(pInfo)).Na me);
}

Hope this would be useful.

-Cnu

[Marc Gravell]

Re: Reflection: How to discover name of a property at run time.

Actually, there is a way for instance properties using lambdas and
Expression (from .NET 3.5); I discussed it here:

http://groups.google.com/group/microsoft.public.dotnet.languages.csharp/browse_thread/thread/f44dc57a9dc5168d/4805324df6b30218

What you have demonstrated are static properties; the same trick can
probably be made to apply - but in reality I doubt either is very
useful or convenient.

Marc

[=?Utf-8?B?VmljdG9y?=]

Re: Reflection: How to discover name of a property at run time.


It does exactly what I have wished for!

Looks a bit scary, but it does the job.

The reason I been looking for that functionality is similar to the one
described in the post you referred to.
In my LINQ to SQL buz layer, to report errors, I have to name LINQ entity
properties to blame as a reason for error.
" .... at the moment I use strings, but if the property name on the class
changes it causes runtime errors whereas I would prefer compile time errors.
To be clear, I want the name of the property and not the value of a property
of an instance. "

The other place where I wished for it, is custom data binding, like
MyFantasticBinf d(this.Textxbox 1, LINQEntity, "Property1" ), where again
Propert1 is a string, and changes to LINQEntity wouldn't be recognized by
compiler.

Please let my voice to JOIN to those who are looking for the nameof(...)
operator.

Victor

[=?Utf-8?B?VmljdG9y?=]

Re: Reflection: How to discover name of a property at run time.

Marc,

thanks again for your reply. Using your code I was able to replace:

AddBusinessErro r("cs_dt_receiv ed", "Received date can't be earlier than date
of loss");
to
AddBusinessErro r<T_ComplainCas e, DateTime?>(x =x.cs_dt_receiv ed, "Received
date can't be earlier than date of complain");

where T_ComplainCase is LINQ to SQL autogenerated class, and cs_dt_received
is one of the properties (i.e. SQL server table's column). This is much
better for me, since now I can be sure that if somebody changes table on SQL
server my code fails when compile.

My question, in you is:
In your post
http://groups.google.com/group/micro...05324df6b30218 you have mentioned that:

"In fact, add in some "this TType obj" and you get type inference... ".
string test1 = foo.MemberName( x =x.Bar);

Can you share that code with us?

Thanks Victor.

[Marc Gravell]

Re: Reflection: How to discover name of a property at run time.

I haven't checked (in a hurry), but:

public static string MemberName<TTyp e>(
this TType type,
Expression<Acti on<TType>member )
{
return MemberInfo(memb er).Name;
}

public static string MemberName<TTyp e, TResult>(
this TType type,
Expression<Func <TType, TResult>member)
{
return MemberInfo(memb er).Name;
}

The "type" argument isn't used except by the compiler for the type-
inference.

Marc

[Marc Gravell]

Re: Reflection: How to discover name of a property at run time.

Looks a bit scary, but it does the job.

That phrase pretty-much describes most manual uses of Expression - a
very confusing subject indeed! For info, though: it looks scary, but
it gets easier with a little practice - you just need to take a very
deep breath before diving in ;-p

Marc

[=?Utf-8?B?VmljdG9y?=]

Re: Reflection: How to discover name of a property at run time.

And they worth diving in!

After looking at your elegant code I’ve realized how important Expressions
might be, and definitely want to spend some time learning more.

Also, when I have incorporated it in my application, I do not see it any
more “as largely "for jollies"”. I feel much more confident in biasness logic
layer now, than when the database fields (i.e. SQL LINQ properties) where
strings in my error reporting methods.

Since my original question was about getting names of the properties, I have
modified your code and introduced a delegate that returns object, so when
looking for a property name, I do not need to specify result type <TType,
TResult>, but just <TType>.

Actually, your code blows on such expressions, since Expression contains
Convert function that your code doesn’t expect ({x =>
Convert(x.cs_dt _received)}).

In the code below expression parsing is 'hard wired' (just for
illustration), so the place for UnitaryExpressi on is visible.

static class MemberUtil
{

public delegate object PropertyNameDel etgate<T>(T x);

public static string GetPropertyName <T(Expression
<PropertyNameDe letgate<T>membe r)
{
return ((MemberExpress ion) ((Expression) ((UnaryExpressi on)
member.Body).Op erand)).Member. Name;
//return MemberUtil.Pars eMemberInfo(mem ber).Name;
}
}


"Marc Gravell" wrote:

Looks a bit scary, but it does the job.

>
That phrase pretty-much describes most manual uses of Expression - a
very confusing subject indeed! For info, though: it looks scary, but
it gets easier with a little practice - you just need to take a very
deep breath before diving in ;-p
>
Marc
>

[Marc Gravell]

Re: Reflection: How to discover name of a property at run time.

I'm glad it was useful, then ;-p

Marc