Global Variable Ends Up as Nothing in Form

  • Thread starter Thread starter Fred Block
  • Start date Start date
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Fred Block

Hi All,

I'm an experienced VB6 developer and now starting (newbee) with VB 2008 and
I'm very excited.

Here's an issue I'm experiencing right off the starting line and cannot make
sense of it:

I have a module (Public) and in it contains a few global variables (String
data type). When I go to use these in a Form the value is "Nothing." Why is
this?
...
Public Module modMain

Public g_strMyPublicVar As String

Then in the form (frmMain), the g_strMyPublicVar does not contain the data
as it was set in modMain.


Any insight is greatly appreciated and I thank you in advance!

Kind regards - Fred
 
Hi All,

I'm an experienced VB6 developer and now starting (newbee) with VB 2008 and
I'm very excited.

Here's an issue I'm experiencing right off the starting line and cannot make
sense of it:

I have a module (Public) and in it contains a few global variables (String
data type). When I go to use these in a Form the value is "Nothing." Why is
this?
..
Public Module modMain

Public g_strMyPublicVar As String

Then in the form (frmMain), the g_strMyPublicVar does not contain the data
as it was set in modMain.

Any insight is greatly appreciated and I thank you in advance!

Kind regards - Fred
Click to expand...

In your post, you didn't assign any value to "g_strMyPublicVar", thus
you may get a null refence exception.

If you do something like this, you won't get an exception.

' In your module, assign a value to "g_strMyPublicVar"
Public Module modMain
' eg: Assign value "foo"
Public g_strMyPublicVar As String = "foo"
End Module

or assign a value to "g_strMyPublicVar" in your form(frmMain) inside a
method:

' In your form, that'll work
Public Class Form1
Sub mymethod()
g_strMyPublicVar = "foo"
End Sub
End Class

' That won't work, if you assign value at class-level
' in your form
Public Class Form1
g_strMyPublicVar = "foo"
End Class

....And as you pointed, you are declaring it in your module so,
assigning a value to "g_strMyPublicVar" in your module should work
when you call it within your form.

Hope this helps,

Onur Güzel
 
Hi All,

I'm an experienced VB6 developer and now starting (newbee) with VB 2008 and
I'm very excited.

Here's an issue I'm experiencing right off the starting line and cannot make
sense of it:

I have a module (Public) and in it contains a few global variables (String
data type). When I go to use these in a Form the value is "Nothing." Why is
this?
..
Public Module modMain

Public g_strMyPublicVar As String

Then in the form (frmMain), the g_strMyPublicVar does not contain the data
as it was set in modMain.

Any insight is greatly appreciated and I thank you in advance!

Kind regards - Fred
Click to expand...

What is the expected value? From what you posted the value should be
Nothing since nothing was assigned.

If you would like to set a value right off the bat, you could do the
following:

//////////
Public MyPublicVar As String = "please drop the hungarian
notation :-)"
/////////

I also hate modules (just my personal preference) and would recommend
you either switch to a static class or implement a singleton class to
expose the properties.

Thanks,

Seth Rowe [MVP]
http://sethrowe.blogspot.com/
 
Hi Onur and thanks!

I found the issue to be that I "accidentally" had the same global variable
in two different modules. VB did not complain however which now puzzles me.

When the code ran I was trying to create a file in a path that did not exist
(System.IO.DirectoryNotFoundException)...

I was using: sw = New StreamWriter(strFile, True)

Is there a parameter I can use or some other way to have the path ctraed if
it does not exist?

Thanks again! - Fred

---------------------------------------
Hi All,

I'm an experienced VB6 developer and now starting (newbee) with VB 2008
and
I'm very excited.

Here's an issue I'm experiencing right off the starting line and cannot
make
sense of it:

I have a module (Public) and in it contains a few global variables (String
data type). When I go to use these in a Form the value is "Nothing." Why
is
this?
..
Public Module modMain

Public g_strMyPublicVar As String

Then in the form (frmMain), the g_strMyPublicVar does not contain the data
as it was set in modMain.

Any insight is greatly appreciated and I thank you in advance!

Kind regards - Fred
Click to expand...

In your post, you didn't assign any value to "g_strMyPublicVar", thus
you may get a null refence exception.

If you do something like this, you won't get an exception.

' In your module, assign a value to "g_strMyPublicVar"
Public Module modMain
' eg: Assign value "foo"
Public g_strMyPublicVar As String = "foo"
End Module

or assign a value to "g_strMyPublicVar" in your form(frmMain) inside a
method:

' In your form, that'll work
Public Class Form1
Sub mymethod()
g_strMyPublicVar = "foo"
End Sub
End Class

' That won't work, if you assign value at class-level
' in your form
Public Class Form1
g_strMyPublicVar = "foo"
End Class

....And as you pointed, you are declaring it in your module so,
assigning a value to "g_strMyPublicVar" in your module should work
when you call it within your form.

Hope this helps,

Onur Güzel
 
Hi Onur and thanks!

I found the issue to be that I "accidentally" had the same global variable
in two different modules. VB did not complain however which now puzzles me.
Click to expand...

Well, actually, it's legal. The full name of a variable in a module is
essentilally, namespace.modulename.variablename. So, a variable in a
different module has a different name...
 
Variables. (Aka, stop with the VB6 global variable concept).

I dare to even go a step further,, in my code you wil not find anny shared
keywords
it is verry easy to just wrap all needed parameters in a parameter class and
pass this back and forward to constructors of classes that need these
parameters

for small projects it is enough to create a base class with the required
properties

regards

Michel
 
Hi Onur and thanks!
Click to expand...
When the code ran I was trying to create a file in a path that did not exist
(System.IO.DirectoryNotFoundException)...

I was using: sw = New StreamWriter(strFile, True)

Is there a parameter I can use or some other way to have the path ctraed if
it does not exist?

Thanks again! - Fred
Click to expand...

Hi Fred,
For the question about checking path, when you use StreamWriter's
constructor specifying a path, new file is created even the file does
not exist in the path that you passed. If it exists, it's
overwritten.

See here:
http://msdn.microsoft.com/en-us/library/36b035cb.aspx

But as you get DirectoryNotFound Exception, it means that file's
"directory" specified in StreamWriter's constructor, is invalid. You
need to enter correct directory, at least.

Additionaly, if you still need to check if a directory is available,
you can use:
"My.Computer.FileSystem.DirectoryExists" in a if-then conditional to
determine.

See it here:
http://msdn.microsoft.com/en-us/library/ax2x538z.aspx

Hope this helps,

Onur Güzel
 
I dare to even go a step further,,  in my code you wil not find anny shared
keywords
it is verry easy to just wrap all needed parameters in a parameter class and
pass this back and forward to constructors of classes that need these
parameters

for small projects it is enough to create a base class with the required
properties

regards

Michel

"sloan" <[email protected]> schreef in bericht
Click to expand...

I agree, whenever plausible I try to put the properties into an
instanced property.

In many of the large applications I work on, I prefer to use a
constructor injection pattern and then have an IoC (inversion of
control) container shove a settings class into any class that requires
it. Takes a bit of time to get used to, but it is extremely powerful
once it's implemented.

Thanks,

Seth Rowe [MVP]
http://sethrowe.blogspot.com/
 
Thanks again Onur - this is exactly what I did to get it to work.

Regards - Fred

------------------------------------
Hi Onur and thanks!
Click to expand...
When the code ran I was trying to create a file in a path that did not
exist
(System.IO.DirectoryNotFoundException)...

I was using: sw = New StreamWriter(strFile, True)

Is there a parameter I can use or some other way to have the path ctraed
if
it does not exist?

Thanks again! - Fred
Click to expand...

Hi Fred,
For the question about checking path, when you use StreamWriter's
constructor specifying a path, new file is created even the file does
not exist in the path that you passed. If it exists, it's
overwritten.

See here:
http://msdn.microsoft.com/en-us/library/36b035cb.aspx

But as you get DirectoryNotFound Exception, it means that file's
"directory" specified in StreamWriter's constructor, is invalid. You
need to enter correct directory, at least.

Additionaly, if you still need to check if a directory is available,
you can use:
"My.Computer.FileSystem.DirectoryExists" in a if-then conditional to
determine.

See it here:
http://msdn.microsoft.com/en-us/library/ax2x538z.aspx

Hope this helps,

Onur Güzel
 
Hi Seth,

Why is hungarian notation not a suggested habit in .NET? Doesn;t it make
coding easier to read? If there is a newer scheme, please share this with
me. I'm very teachable and want to do this right the first time.

VB 2008 book suggestions?

Thanks in advance to you Seth (and all others answering my thread).

Regards - Fred

------------------------------------------------

//////////
Public MyPublicVar As String = "please drop the hungarian
notation :-)"
/////////

I also hate modules (just my personal preference) and would recommend
you either switch to a static class or implement a singleton class to
expose the properties.

Thanks,

Seth Rowe [MVP]
http://sethrowe.blogspot.com/
 
I agree. Using a small parameter-wrapper class is the way to go. It takes
disjoint properties and adds some cohesion to them.


One idea that a former colleague showed me...was to take this small wrapper
class...and put it into a "DataStore" (for a winforms app, it was basically
a singleton where you could keep/add/remove some objects).

The main form would create and put the small parameter-wrapper class into
the DataStore (using a unique key).

The DataStore would pull the small-wrapper-parameter class (actually remove
it at the same time)....using the same unique key.

This way.....the form could be instantiated from anywhere. Just "put into
the DataStore", then call the form.

Either way is good, just throwing a different nugget out there.
 
Why is hungarian notation not a suggested habit in .NET? Doesn;t it make
coding easier to read? If there is a newer scheme, please share this with
me. I'm very teachable and want to do this right the first time.
Click to expand...

http://en.wikipedia.org/wiki/Hungarian_notation#Disadvantages_of_Systems_Hungarian

I prefer to just use names that make sense, no special notation at
all. If your methods are short and concise and have a single
responsibility, most likely there will be few variables that are
easily understood by assignments, and special notations aren't
required. I am also an advocate against using abbreviations in
variable names, as they hurt readability (unless they are truly
accepted acronyms like "guid" for globally unique identifier).

Most times I end up using the type name with a lowercase first letter,
unless a more specific name is required.

Dim notificationService As New NotificationService()
Dim dataStore As IDataStore = GetCustomerDataStore()
Dim message As String = "The name 'string' wouldn't make sense here"

Later versions of .NET added in implicit typing which can shorten
these declarations. However due to the confusion between implicitly
typed variables and the rubbish done in VBScript, I dislike it. I much
prefer the C# approach of using the 'var' keyword. Below are the same
samples (if you desire to use the feature)

Dim notificationService = New NotificationService()
Dim dataStore = GetCustomerDataStore()
Dim message = "I love putting messages inside strings"
VB 2008 book suggestions?
Click to expand...

Book recommendations have never been my strong suit, mainly because I
don't read many (shame, shame I know). My recommendations would be to
hit the library and see if they have any, or even better try to find a
local .NET university or other training event. Being involved in the
community is the best way to learn.

Thanks,

Seth Rowe [MVP]
http://sethrowe.blogspot.com/
 
My recommendations would be to
hit the library and see if they have any, or even better try to find a
local .NET university or other training event.
Click to expand...

I should clarify, I didn't mean going to a University and taking a
college class, .NET universities are sessions about new Microsoft
features etc:

http://www.dotnet-u.com/

Not sure if they have any near you, but it's worth checking out. You
might also look up your local Microsoft Developer Evangelists and
contact them for upcoming events (USA thing only I believe, so it
might not be applicable to you):

http://msdn.microsoft.com/en-us/bb905078.aspx

Thanks,

Seth Rowe [MVP]
http://sethrowe.blogspot.com/
 
Hi Seth and thanks again!

Point taken and I found just about all I needed in the MSDN I installed here
on the topic. This all makes sense and before I get ANY further with this
first .NET project I've taken on, I'll undo the old VB6 notations I was
using. A lot has changed!

Regards - Fred
 
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