Re: Accessing Shared Properties of a Parent Windows App from Class
- From: Jon Ebersole <JonEbersole@xxxxxxxxxxxxx>
- Date: Sun, 5 Nov 2006 06:49:01 -0800
Thank you Jeff. That is very good information and would be very relevant if
my class library was in the same project as my windows forms. Unfortunately,
my class library is a stand-alone class library and is its own VS 2005
Project. My Windows Forms app is its own project, and my Windows Service is
its own project. All three of these projects are contained in one VS 2005
Solution. Both projects have a reference to my class library project, since
they both use the same objects.
My class library doesn't have the 'My.Forms' namespace available, because it
doesn't have any Windows Forms in it. I can't add a reference to the Windows
Forms project from my Class Library, because that would cause a circular
reference.
So does that leave me with only option 2 from your message; individually
send a SQLConnection reference for each call to my DB Connection object?
Isn't there anyway that I can reference the calling assemblies main form
properties from an instantiated external child class? Something like...
(from my db connection object within my external class library)
Me.GetType.Assembly.GetCallingAssembly.xxx.xxx.MainForm.DBConnection
Where xxx.xxx would be some reference to the main form somehow?
Thanks for your valuable input.
--
Jon Ebersole
Microsoft Certified Solution Developer
"Jeffrey Tan[MSFT]" wrote:
Hi Jon,.
Based on my understanding, your winform application is creating some other
class library objects to implement business logic. All these class library
objects need the SQLConnection object to manipulate the database. So you
want to find a way to create the SQLConnection once and share it with all
the class library objects for efficiency. If I have misunderstood you,
please feel free to tell me, thanks.
Yes, this is a common task. The keypoint in this task is that how to get the
reference to the mainform object. There are several ways to get it done. For
example:
1. You may change the declaration of shared DBConnection object from
"Protected" to "Public". Then in each MyLibrary.MyObject constructor, you
may refer this shared DBConnection object with
"[mainForm_classname].DBConnection". This is because the "DBConnection" is a
shared object, there is no need to refer it with mainform object reference,
the mainform class name is enough to refer the public shared field/member.
2. In declaring the MyLibrary.MyObject constructor, you may add an extra
parameter of type DBConnection. Then whenever you are creating the
MyLibrary.MyObject in man form, you may pass the DBConnection object
reference in it. In this approach, there is no need to mark the
"DBConnection" as "shared".
3. If you are using VB2005, the VB2005 compiler provided a new featured
named "My Namespace". This feature allows us to refer a lot of useful
members staticly without the object references. So you may just use
"My.Forms[0]" to get the mainform reference in the MyLibrary.MyObject
constructor, then you may cast the reference into the mainform type(since
the reference you have got is of base type "Form"). Finally, you may use the
"mainform_reference.DBConnection" to get the DBConnection object now. In
this approach, there is no need to mark the "DBConnection" as "shared".
Please see the "The My Namespace" section in the article below for more
information regarding this new feature:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnvs05/html/vb2005_overview.asp
Additionally, if you are curious about how VB2005 compiler implement this
cool "My Namespace" feature, I have provided some insight in the discussion
thread below, just for your reference:
http://groups.google.com/group/microsoft.public.vsnet.debugging/browse_thread/thread/d08b27dbd8ffe82e/cf909a3a4963b1e7?lnk=st&q=VB2005+MY+msdn+microsoft+%22Jeffrey+Tan%22&rnum=1&hl=zh-CN#cf909a3a4963b1e7
Hope this helps.
Best regards,
Jeffrey Tan
Microsoft Online Community Support
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