Joe Rojas
JRojas at tnco-inc.com
Mon Mar 17 12:22:58 CST 2003
John, Looking at the couple of coding examples that you have posted, both here and on the AccessD list, I keep getting this feeling that I am reading Java code. :-) A lot of the keywords, and their uses, look exactly the same as Java and I would assume that they work the same too. This sounds promising for the .Net platform because Java is very cool, IMO! Your excitement towards VB.Net reminds me of how I felt when I started learning Java. My ignorance of the whole .Net stuff made me skeptical about it, but it sounds like it is worth a look! I really enjoy your updates that you post as you learn VB.Net, I find them very useful! -Joe -----Original Message----- From: John W. Colby [mailto:jcolby at colbyconsulting.com] Sent: Saturday, March 15, 2003 9:24 AM To: dba-vb at databaseadvisors.com Subject: RE: [dba-VB] VB.Net stuff Jim, I am reading Programming Visual Basic .Net by Francesco Balena - ISBN 0-7356-1375-3. Given that it is the only book on the subject I have I can't compare it to anything but it has done a good job of explaining the basics so far. It does assume that you are a VB6 programmer (which I am not) and know that pretty well, so if you have no VB experience it might be an even steeper learning curve. OTOH, so much has changed from VB (apparently) that I am not even sure how important it is to know that stuff. Apparently the dev environment is completely different, the language now has true implementation inheritance (inherits the functionality and interface instead of just the interface) and is really just a thin layer over the .Net framework of a few thousand classes and interfaces. Implements is a keyword that tells the compiler that you are implementing an interface. Interfaces are still useful in cases where the actual implementation is so specific to what you are doing that trying to inherit code wouldn't be helpful, yet you still want to define a standard interface so everyone does things the same way. IEnumerable is an interface for enumeration, which of course is the process of enumerating a set of objects, handing back one object every time you are called. The hard disk makes a good example, the class initializes, starts to read the dir structure and file names. Each time the class is called, it finds the next directory / file and hands back some property or property (a string in this case with the name of the file). The class keeps track of where it is in the disk structure so that the next time it is called it knows where to go (into subdirectories for example) to get the next file property. .Net the framework is a truly awesome collection of classes that wrap the entire windows API, as well as classes which build up other useful functionality. There are collection classes, which are subclassed to make stacks and queues. Need a stack? It's in there. Need a stack that does something special? Inherit it and implement your own custom functionality. There are classes for encryption, literally perhaps 50 lines of code to open a file (a class), feed the text stream to the encryption class, feed the encryption stream to a class that transmits the stream out over the internet. Let's not pretend that I have any idea how to do this yet, but I know that these classes exist. and with true inheritance, tweaking existing stuff to do what you need has to be a bajillion times faster that writing it yourself from the ground up. Of course you have to learn the namespaces and where all this stuff is, as well as how to use the individual classes once you know where they are. John W. Colby Colby Consulting www.ColbyConsulting.com -----Original Message----- From: dba-vb-admin at databaseadvisors.com [mailto:dba-vb-admin at databaseadvisors.com]On Behalf Of Jim Lawrence (AccessD) Sent: Saturday, March 15, 2003 2:23 AM To: dba-vb at databaseadvisors.com Subject: RE: [dba-VB] VB.Net stuff Hi John: Looks like awesome stuff. I have been wandering around the side of the .net pool for a while and will eventually have to jump in...but learning this coding will be like climbing 3000 vertical feet with two pack-sacks on. What is a 'Implements IEnumerable' anyway? Modules? Classes and internal sub-classes with functions and subroutines floating around? This looks like something that will take more than an evening to master. 8-/ I bet there is no books that will read 'Master .Net in 24 hours'. Nothing like a good challenge...:-) Any recommendations for a good book to start? Jim -----Original Message----- From: dba-vb-admin at databaseadvisors.com [mailto:dba-vb-admin at databaseadvisors.com]On Behalf Of John W. Colby Sent: Friday, March 14, 2003 5:41 PM To: AccessD Cc: VbAdmin; VBA Subject: [dba-VB] VB.Net stuff I thought you folks might be interested in looking at some of the features that .net exposes. The following is a class directly from "Programming VB.net" by Francesco Balena. It is fascinating (to me anyway) as it clearly displays the usage of a whole slew of functionality built in to the .net environment. It was really an exercise in demonstrating the ability to add enumerators to any class (where appropriate) so that people using your class could use "for each" constructs with your classes. This class iterates a disk path and returns the file name of each file or directory in turn. Please let's not get in to a "it could have been so much simpler". I have no idea whether that is true, and really don't much care. In fact I don't even understand all that is happening here! I am simply showing the code so that anyone who is interested can see how the author uses built in classes such as IEnumerator, and the built in stack class of the Systems.Collection namespace. Seriously cool built in functionality ready to be built upon. I built a wrapper function: Module Module1 Function TestGetEnumerator(ByVal strRoot As String) As String Dim f As System.IO.FileInfo Dim str As String 'enumerate all files in strRoot directory tree For Each f In New FileTree(strRoot) str = str & f.FullName & vbCrLf Next TestGetEnumerator = str End Function End Module Which I then used in the OnOpen event of a form to return a string of all the files and directories in a given path (hard coded), which I then place into a text box on a form. What I want to do is have the function be the datasource for a combo or list but I couldn't figure that out and needed to move on. ;-) The result is an EXE which I could mail to you which opens the form and displays the file names. Of course I can just as easily use the file name to do some processing on that file, likewise the class could be modified to return any of the file attributes - size, created date etc. The EXE is ~10k but of course requires that you have the .net environment on your computer. Anyone that uses the Windows Update feature to keep their system up to date with all of the latest patches has probably been offered the ability to download and install the .net environment needed to run my 10k exe. Anyway, the class is as follows - all copyrights belong to their owners, not me. Public Class FileTree Implements IEnumerable 'The search Path Public ReadOnly DirPath As String 'The constructor Sub New(ByVal DirPath As String) Me.DirPath = DirPath End Sub 'Return an enumeraable object(an instance of the inner class) Function GetEnumerator() As IEnumerator _ Implements IEnumerable.GetEnumerator Return New FileTreeEnumerator(DirPath) End Function 'The IEnumerator private object Class FileTreeEnumerator Implements IEnumerator Dim DirPath As String 'This variable contains the Enumerator object for the file list 'in the dir being scanned Dim FileEnumerator As IEnumerator 'This variable contains the stack of the Enumerator objects 'for subdirs of all pending directories Dim DirEnumerators As New System.Collections.Stack() 'a simple constructor Sub New(ByVal DirPath As String) 'Save the dir path Me.DirPath = DirPath 'manually call the reset method Reset() End Sub Sub Reset() Implements IEnumerator.Reset 'The dir object that represents the root object Dim di As New System.IO.DirectoryInfo(DirPath) 'get the Enumerator object for the file list, and reset it FileEnumerator = di.GetFiles.GetEnumerator FileEnumerator.Reset() 'get the enumerator object for the subdirectory list Dim dirEnum As IEnumerator = di.GetDirectories.GetEnumerator dirEnum.Reset() 'push it onto the stack DirEnumerators.Push(dirEnum) End Sub Function MoveNext() As Boolean Implements IEnumerator.MoveNext 'simply delegate to the file enumerator object If FileEnumerator.MoveNext Then 'it returned true so we can exit Return True End If 'if there are no files in the current directory, check 'for another subdirectory in the cuurrent directory Dim dirEnum As IEnumerator = _ CType(DirEnumerators.Peek, IEnumerator) 'check whether current subdirectory enumerator has more items Do Until dirEnum.MoveNext 'There are no more subdirectories on this level 'so we must pop another element of the stack DirEnumerators.Pop() If DirEnumerators.Count = 0 Then 'return false if no more subdirectories to scan Return False End If 'get the current enumerator dirEnum = CType(DirEnumerators.Peek, IEnumerator) Loop 'We can create a DirectoryInfo. Dim di As System.IO.DirectoryInfo = _ CType(dirEnum.Current, System.IO.DirectoryInfo) 'Store the file enumerator and reset it FileEnumerator = di.GetFiles.GetEnumerator FileEnumerator.Reset() 'Get the enumerator for the subdir list 'and reset it dirEnum = di.GetDirectories.GetEnumerator dirEnum.Reset() 'push it onto the stack DirEnumerators.Push(dirEnum) 'recursive call to process the file enumerator Return Me.MoveNext End Function 'The current property simply delegates to FileEnumerator.Current ReadOnly Property Current() As Object Implements IEnumerator.Current Get Return FileEnumerator.Current End Get End Property End Class End Class John W. Colby Colby Consulting www.ColbyConsulting.com ---------------------------------------------------- Is email taking over your day? Manage your time with eMailBoss. 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