What does my program do?
As at 05 May 2021
This program was developed with the language VB.Net, the .NET framework 4.8 and with Visual Studio 2019 CE. The point of this program is to run a rudimentary database. The view is similar to a classic Internet forum—there are threads, in the threads there are different numbers of postings and in each post there are different numbers of pictures and long texts. If the thread is selected using the ComboBox, all posts with their images and texts are displayed one below the other. When you click on a specific post, only its images are displayed. Since the database is only intended for the company's products, it was decided not to use categories (e.g. images vs. videos vs. offtopic because it doesn't make any sense) and sub-categories (e.g. electrical vs. wood products).
When the program is closed, you will be asked whether the data should be saved. (still in the beta version). These data are read in when the program is loaded. If images are not found, their paths will be displayed in a window.
The user also has the option of searching through all threads and viewing the results with various sorting options. In this case, only the posts found are listed in the ListBox, and here, too, the user can select individual posts and have them displayed enlarged.
The program reads in the user data when it starts. A user can log in and, depending on his role, has certain power to make decisions. A “normal” user can create threads and posts, but only an administrator or moderator can edit and delete posts; and block a user. If you are not logged in or if you are locked, you can only read threads and posts.
The number of contributions is counted for each user. In the future, it should be possible to give a user stars.
About the classes
There is the Form1.vb class, and three other important classes: Class_Forum, Class_Post and Class_Thread. There is also the Class_User class. If a new post is created, this instance of Class_Post is added to a List(of Class_Post), which is located in Class_Thread (“The thread knows which posts it has”). Class_Post has a member ‘Made_by’, which is an instance of the Class_Users (“Every post knows which user made it”). Class_Post contains the member ‚Bilder‘ (=Images), which is a List(Of Bitmap). That is, every instance of class_post has got a List(of Bitmap).
There are also several forms for 1) editing, deleting posts, 2) for blocking or unblocking users, 3) for displaying enlarged images, 4) for logging in, 5) for displaying when images are not loading found, 6) to open the thread, 7) to post.
When the program is started, i.e. when data is read in, the thread instances and post instances are created.
To do list:
1.)
I would like, however, that only the images are in the RAM, which belong to the thread selected with the combobox1. My question is: Do I have to dispose all unnecessary images and read them in again when required? Do we get that built in?
This is my Code to load the data from the formatted txt file. I have a feeling, somewhere in here, or immediately after here, I have to do something.
Private Sub Daten_laden()
Dim Pfad As String 'file path
Using OFD1 As New CommonOpenFileDialog
OFD1.Title = "Textdatei auswählen"
OFD1.Filters.Add(New CommonFileDialogFilter("Textdatei", ".txt"))
OFD1.InitialDirectory = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments)
Dim Result As CommonFileDialogResult
Me.Invoke(Sub() Result = OFD1.ShowDialog())
If Result = CommonFileDialogResult.Ok Then
Pfad = OFD1.FileName
Else
Return
End If
End Using
Dim Pruef_Anzahl_Posts_in_dem_Thread As Integer = 0 'Check number of posts in the thread
Dim Liste_mit_den_Pfaden As List(Of String) 'List with file paths
Dim Liste_mit_den_Bildern As List(Of System.Drawing.Bitmap)
'read all Text
Dim RAT() As String = System.IO.File.ReadAllLines(Pfad, System.Text.Encoding.UTF8)
Pfade_von_nicht_gefundenen_Bildern = New List(Of String) ' Paths of not found images
For i As Integer = 3 To RAT.Length - 2 Step 1
Liste_mit_allen_Threads.Add(New Class_Thread(RAT(i)))
Me.Invoke(Sub() RaiseEvent Es_wurde_ein_neuer_Thread_eroeffnet()) 'A new thread has been opened
Pruef_Anzahl_Posts_in_dem_Thread = CInt(RAT(i + 1))
For j As Integer = (i + 2) To RAT.Length - 2 Step 1
Liste_mit_den_Pfaden = New List(Of String)
Liste_mit_den_Bildern = New List(Of Bitmap)
Dim Index As Integer
Dim Die_ID_des_Nutzers_der_den_Post_erstellt_hat As ULong = CULng(RAT(j + 4)) 'The ID of the user who created the post
For u As Integer = 0 To alle_Nutzer_Liste.Count - 1 Step 1
If alle_Nutzer_Liste(u).ID = Die_ID_des_Nutzers_der_den_Post_erstellt_hat Then
Index = u
Exit For
End If
Next
Dim neuerPost As New Class_Post(RAT(j), RAT(j + 1), CUShort(RAT(j + 2)), Liste_mit_den_Bildern, CDate(RAT(j + 3)), Liste_mit_den_Pfaden, alle_Nutzer_Liste(Index))
'how many threads are there already
Dim wie_viele_Threads_gibt_es_bereits As Integer = Liste_mit_allen_Threads.Count
Liste_mit_allen_Threads(wie_viele_Threads_gibt_es_bereits - 1).Posts_in_diesem_Thread.Add(neuerPost)
' Set the index to the last possible one in the ComboBox. This causes the program to run into the Selected Index event and SI becomes the selected index.
Me.Invoke(Sub() ComboBox1.SelectedIndex = Liste_mit_allen_Threads.Count - 1)
j += 5
Do
Liste_mit_den_Pfaden.Add(RAT(j))
If System.IO.File.Exists(RAT(j)) Then
Liste_mit_den_Bildern.Add(New Bitmap(RAT(j)))
Else
Pfade_von_nicht_gefundenen_Bildern.Add(RAT(j))
End If
j += 1
Loop Until RAT(j) = "#" ' Marker: a post is over
If RAT(j + 1) = "" AndAlso RAT(j + 2) = "" Then ' A new thread is marked with 2 blank lines one below the other.
i = (j + 2)
Exit For
End If
Next
Next
Me.Invoke(Sub() alle_Posts_in_diesem_Thread_anzeigen()) 'show all posts in this thread
If Pfade_von_nicht_gefundenen_Bildern.Count > 0 Then ' In Case something went wrong
Using FBNG As New Form_Bild_nicht_gefunden
FBNG.Datei_anzeigen(Pfade_von_nicht_gefundenen_Bildern)
FBNG.ShowDialog()
End Using
End If
End Sub
On this image, the thread is being switched using the combobox which changes the variable SI which I use often. In this example, the thread Caucasian contains 1 post which contains 2 images. Which means, (still in this moment) I don't need images form shepherds thread
It is not wise to keep all data in RAM. When your database grows, there will be a time that there is too much data.
To overcome this problem, people invented databases: the data is saved on a disk, and only the data that you request is put into memory. Smart databases will keep important data and often used values in memory, to minimize the request time.
If I look at your program, it seems that you only have to change the display after operator input. Operator input is relatively slow: you're a good typist if you can type more than 3 character per second. Usually the response time after operator input is not a problem: if you get the data within half a second, no one will complain.
For a modern computer half a second is enough time to examine a million records. In your application a database won't be a problem.
So my advice would be: start using a database and load only the data that is needed right now, instead of reading all data at startup. Only if you experience long request times, consider to load data that you expect you will need very soon.
Alas, to use a database you will need to learn something new: at least how to structure a databases. If I look at your tables, I have the impression that you already mastered this. Furthermore you'll have to learn how to add / query / update / remove data. This is usually done using SQL or software that supports LINQ, like entity framework.
It seems to me that your queries are quite limited in number: you won't have hundreds of different queries. If you already know SQL, and you don't think you need to know entity framework in the near future, I would go for accessing the database using SQL.
If you don't know SQL very much, or if you need to do an awful lot of different queries, consider to access the database using LINQ. This requires entity framework.
If you haven't got a database already, my first shot would be to use SQLight: a database in one file, fast enough for your application.
If you hide properly that you use SQLight, migrating to a smarter database if the need arises won't require a big change in your application.
class Repository
{
public long AddPost(Post post) {...} // add Post to the database, returns the Id
public long AddUser(User user) {...}
...
// fetch all Posts of a User:
public User FetchUserWithHisPosts(int userId);
// fetch Posts of a User after a certain data:
public User FetchUserWithHisPosts(int userId, DateTime startDate);
...
}
A Repository is some kind of warehouse: all you know is that you can store items in it, and later retrieve them, even after your computer is restarted.
The Repository hides how it does this: the constructor might load everything in memory (like your current application), it could also be that the repository uses SQLight, or a smarter database, or even Entity Framework.
A good way to migrate would be to first translate your current application such that everyone only accesses the data using the Repository. The Repository accesses your "in-memory data" which is in a separate class that is loaded at startup.
Later you can change the repository such that it doesn't use the "in-memory data" anymore, but accesses the database: users of your repository won't have to change.
About loading pictures
No, you don't have to load all pictures at startup. It will be fast enough to load the pictures only when shown: after all, you won't be showing 1000 pictures on the screen at once.
As a picture uses a lot of memory, it is wise to Dispose() the picture as soon as you don't need it anymore:
Image GetImage(long imageId)
{
Repository repository = new Repository();
return repository.GetImageById(imageId);
}
void DisposeImage(Image image)
{
image.Dispose();
}
You hide how you Load the image, and how you free up memory after an Image is not needed anymore. This makes it easier to change this, might the need arise later. It also makes your code easier to read and to unit test.
Hello #Harald Coppoolse,
I thank you for your detailed and understandable answer. Admittedly, I have to look at and learn those SQL (Light) and Entity procedures.
For now, I've temporarily made sure that I only load the pictures that are shown and dispose all the others. I coded this as follows:
Private Sub ComboBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox1.SelectedIndexChanged
If ComboBox1.SelectedIndex <> (-1) Then
SI = ComboBox1.SelectedIndex
If Programm_fertig_geladen Then
Load_the_pictures_only_when_shown_and_free_up_memory_after_an_Image_is_not_needed()
End If
alle_Posts_in_diesem_Thread_anzeigen()
End If
End Sub
Private Sub Load_the_pictures_only_when_shown_and_free_up_memory_after_an_Image_is_not_needed()
For g As Integer = 0 To Liste_mit_allen_Threads.Count - 1 Step 1
If g <> SI Then 'Diese Bilder verwerfen
For i As Integer = 0 To Liste_mit_allen_Threads(g).Posts_in_diesem_Thread.Count - 1 Step 1
For j As Integer = 0 To Liste_mit_allen_Threads(g).Posts_in_diesem_Thread(i).Bilder.Count - 1 Step 1
Liste_mit_allen_Threads(g).Posts_in_diesem_Thread(i).Bilder(j).Dispose()
Liste_mit_allen_Threads(g).Posts_in_diesem_Thread(i).BoolArray(j) = False
Next
Dim CNT As Integer = Liste_mit_allen_Threads(g).Posts_in_diesem_Thread(i).Bilder.Count
For z As Integer = (CNT - 1) To 0 Step -1
Liste_mit_allen_Threads(g).Posts_in_diesem_Thread(i).Bilder.RemoveAt(z)
Next
Next
Else 'Diese Bilder laden
'für jeden Post
For i As Integer = 0 To Liste_mit_allen_Threads(g).Posts_in_diesem_Thread.Count - 1 Step 1
'die Bilder in dem Post
For j As Integer = 0 To Liste_mit_allen_Threads(g).Posts_in_diesem_Thread(i).Pfade_der_Bilder.Count - 1 Step 1
Dim neu_geladenes_Bild As New Bitmap(Liste_mit_allen_Threads(g).Posts_in_diesem_Thread(i).Pfade_der_Bilder(j))
If Liste_mit_allen_Threads(g).Posts_in_diesem_Thread(i).BoolArray(j) = False Then
Liste_mit_allen_Threads(g).Posts_in_diesem_Thread(i).Bilder.Add(neu_geladenes_Bild)
Liste_mit_allen_Threads(g).Posts_in_diesem_Thread(i).BoolArray(j) = True
End If
'End Using
Next
Next
End If
Next
End Sub
I built a Boolean array into the Class_Post, which has as many members as there are images and paths in the post. The purpose of this is to make sure that I remember which pictures are there and which are not.
When disposing of the images of a post, the respective array member is set to false.
When reloading the images of a post, the respective array member is set to True.
Dispose alone is not enough, because funnily enough, the place in the List(of Bitmap) remains occupied. You also have to completely delete the picture with RemoveAt, but in a backward running for loop, because the list gets smaller during the deletion. ;)
Using cannot not be used.
I have a very simple code in a VB.NET program to load all paths in a folder in a text box. The code works great, the problem is that it adds the lines in real time, so it takes about 3 minutes to load 20k files while the interface is displaying line by line.
This is my code:
Dim ImageryDB As String() = IO.Directory.GetFiles("c:\myimages\")
For Each image In ImageryDB
txtbAllimg.AppendText(image & vbCrLf)
Next
How can I force my program to load the files in chunks or update the interface every second?
Thanks in advance
Yes, you can do that. You'll need to load the file names into an off-screen data structure of some kind rather than loading them directly into the control. Then you can periodically update the control to display whatever is loaded so far. However, I think you'll find that the slowness comes only from updating the control. Once you remove that part, there will be no need to update the control periodically during the loading process since it will be nearly instantaneous.
You could just load all of the file names into a string and then only set the text box to that string after it's been fully loaded, like this:
Dim imagePaths As String = ""
For Each image As String In Directory.GetFiles("c:\myimages\")
imagePaths &= image & Environment.NewLine
Next
txtbAllimg.Text = imagePaths
However, that's not as efficient as using the StringBuilder:
Dim imagePaths As New StringBuilder()
For Each image As String In Directory.GetFiles("c:\myimages\")
imagePaths.AppendLine(image)
Next
txtbAllimg.Text = imagePaths.ToString()
However, since the GetFiles method is already returning the complete list of paths to you as a string array, it would be even more convenient (and likely even more efficient) to just use the String.Join method to combine all of the items in the array into a single string:
txtbAllimg.Text = String.Join(Environment.NewLine, Directory.GetFiles("c:\myimages\"))
I know that this is not an answer to your actual question, but AppendText is slow. Using a ListBox and Adding the items to it is approx. 3 times faster. The ListBox also has the benefit of being able to select an item easily (at least more easily than a TextBox)
For each image in ImageryDB
Me.ListBox1.Items.add (image)
Next
However, there is probably an even more useful and faster way to do this. Using FileInfo.
Dim dir As New IO.DirectoryInfo("C:\myImages")
Dim fileInfoArray As IO.FileInfo() = dir.GetFiles()
Dim fileInfo As IO.FileInfo
For Each fileInfo In fileInfoArray
Me.ListBox2.Items.Add(fileInfo.Name)
Next
I am currently making a vb program that i plan to make very big. I have a decent knowledge of visual basic but today i came across something i do not understand. Because of the huge size of my program , i decided to try and keep the program as organized as possible by putting specific subs in modules. These subs consist of httprequest , webbrowsers(control), webclients and alot of loops. In order to prevent these subs from lagging my main application i thread them using threading.thread and i start them from my main form. But this leads to two problems.
Problem 1: The threads cannot in any way interact with the main form.
Once the a httprequest or webclient collects the information from my desired website, i am trying to make it add the info to a listbox in my main form, So what i did is it typed
Msgbox("Info Sent")
form1.listbox1.items.add(String)
The first messagebox will show but although the code right under it runs, nothing is added to the first forms listbox.I am not using delegates to transfer the information, instead, although its not a good habit, i am using checkforillegalcrossovers.
Problem 2: Threading with a webbrowser.
Threading with a webbrowser using threading.thread also does not work because it causes an active x error. After looking it up i found that a solution was to use a single threaded apartment but this would not work because i may need multiple threads running off the same sub at once.
One solution that i have found to this problem is creating another form completely and setting it invisible, and since the form is its own thread i do not need to use threading.thread , but the problem comes when i am trying to create multiple threads, or else i can somehow dynamically create the threads and put the subs inside of it programically this method wont work And even if it does i feel that it is sloppy so i will leave this for one of two last resorts.
The other solution is the most simple one in which i just put all of the code in the main form, but if i keep on doing that form1 is gonna become huge and sloppy, doing this wont solve the webbrowser problem either and even when using regions i still feel that something that 1000+ lines deserves its own class.
There must be some solution out there that solves these problems. Any help would be appreciated, Thanks.
I checked my code for updating the progress bar, and using a single thread with synclock will NOT work. They way I make it work is perform the step of the pbar each time after a thread is started as I have limited total threads (say less than 5 threads). Thus, even the progress bar steps before the threads are finished, but it will not progress further before new threads started. It is not 100% accurate but it more or less telling the progress
'update the progress bar
some_form.PBar1.PerformStep()
' This while loop is to count the existing running thread,
' and determine whether new thread should start
While 1
Dim t2 = New System.Threading.Thread(Sub() WaitForPermission())
t2.Start()
t2.Join()
If proceed_gen Then
Exit While
End If
End While
'Start doing what I need to do
Dim t1 = SomeSub()
t1.Start()
'End of code, as VB doest not have thread.detach()
Correct me if I am wrong, but you probably have to use a background worker. I know this is annoying, but this is the limitation of VB.net.
Or, you can have something like this (pseudo code, not tested)
structure some_struct
'define the strings you want to update, and their status such that
'main() knows if you need to update the stuff to the form
' You can also put how many threads are running, and the status of each thread,
'such that the main knows if all threads are completed
end structure
sub your_sub()
'Manipulate the website, and update the data structure with
'proper stuff you need
end sub
sub main(){
dim t1 = New System.Threading.Thread(Sub() your_sub())
t1.start()
' I am listing only one threads here, but start as many as you want
'check if there are strings that you need to update to the form
while 1
'check if there are any stuff you want to update from the data structure.
' Make sure you use synclock on the data structure, so each thread won't fight each other on accessing the data struct
dim should_update as boolean = false
should_update = 'Something thatyou should implement to judge whether you should update the form.
'You can start a thread and join it so the thread won't fight with other threads for accessing the data structure
dim some_string as string
if should_update
some_string = 'You may also need a thread to join to get the stuff you need. Dim the string as an array if it is required.
'You can also try pass by ref
'if you need to use thread to access the data structure to know if you need to update the form
form1.listbox1.items.add(some_string )
end if
end while
end sub
This is an ugly solution, but it will help you do the job...
I hope you can help with what is probably a naive use of Streams in VB.net.
I have a program that batch processes images and am running out of memory making repeated use (in a loop) of the following:
Using str As Stream = File.OpenRead(file_stem + CStr(file_number) + "." + file_extension)
temp_img = Image.FromStream(str)
str.Close()
End Using
PictureBox1.Image = temp_img
bm = PictureBox1.Image.Clone
temp_img is globally declared Dim temp_img As Image. bm is declared in the same Sub routine as the loop Dim bm As Bitmap.
As the program runs I can see in Task Manager the memory usage rising and then it crashes with an out of memory error. It's as if each time I am using the Stream it is keeping the memory used. What am I doing wrong here?
EDIT:
This thread appears to have gone cold now, but I thought I would share my "work around" for this. It would seem that this is a VB.net bug as the way I have fixed it is to add a MsgBox which is shown only one, immediately prior to the first call to the subroutine that processes sets of 60 images. I ran a single job that processed 96 sets of 60 images and the memory usage didn't rise above about 45MB. The important thing that makes me think it is a bug is that I only show the MsgBox before the first set of 60 and all are run in series. Showing an MsgBox shouldn't fix anything in itself anyway!
I have been creating multiple background threads to parse xml files and recreate new xml files. Now the problem I am having is that even though I use synclock on global variables, I will still at times get errors and I am sure that this is just the crude way of coding I am doing, but I was wondering if someone had a better option.
program flow =
access local folder and upload all files into list
strip each file into xml entries and put these entries into an arraylist
parse for specific values and enter these values into a database table
now create a thread and take the arraylist of entries and the thread will reparse
thread parses and creates a new xml file
main thread continues with another function and then goes and get a file from list
I will add some code to show problem areas but if I have declared global variable in use does the different threads overwrite that value in the variable causing contamination.
For Each g In resultsList
gXmlList.Add(g)
Next
Dim bgw As New BackgroundWorker
bgw.WorkerSupportsCancellation = True
AddHandler bgw.DoWork, New DoWorkEventHandler(AddressOf createXML)
AddHandler bgw.RunWorkerCompleted, AddressOf WorkComplete
threadlist.Add(bgw)
bgw.RunWorkerAsync()
Private Sub createXML()
num += 1
Dim file As String = Module1.infile
xmlfile = directoryPath & "\New" & dateTime.Now.ToUniversalTime.ToString("yyyyMMddhhmmss") & endExtension
Thread.Sleep(2000)
Dim doc As XmlDocument = New XmlDocument
**xwriter = New XmlTextWriter(xmlfile, Encoding.UTF8)** this is where ioexception error
xwriter.Formatting = Formatting.Indented
xwriter.Indentation = 2
xwriter.WriteStartDocument(True)
xwriter.WriteStartElement("Posts")
I have global variables through out the app and should I be locking each one and does this not make using threads then useless.
Dim j As Integer = 0
I believe your biggest problem is not knowing what features in .Net are thread safe. A list for example is not (a dictionary is). While you may get away with it you will eventually run into problems with locking, etc.
Your using classes and variables that are not thread safe. Any time you are working with threads you have to be Extremely careful with locking. To answer your question, yes, you have to lock and unlock everything you are working with unless the type / method specifically handles it for you.
There are a lot of multi threading (PLINQ for example) in .Net 4.0 which handle a lot of the "grunt work" for you. While you should learn and understand how to do thread safe code yourself it will give you a head start.
Try passing the data into the createXML() method. That may help isolate the code from other data being accessed. I would suggest reading up on threading and learning how to do it without a background worker.
Global variables are generally a bad idea. Given your VB code I'm guessing this is a carry over from the VB6 world for you. That's not in any way intended to be insulting, just trying to help advance your skills forward. Variable scope should be as confined as possible.
Another thought looking at your code is to learn how to use String.Format() when building strings / paths.
Simple manual thread in VB to get you started:
Dim bThread As New Threading.Thread(AddressOf createXML)
bThread.IsBackground = True
bThread.Start()
Well if you are having issues with thread locking then you can simply wrap your action in the following manor.
'This will need to be out of scope so that all threads have access to it
Dim readerWriterLock As New Threading.ReaderWriterLockSlim
readerWriterLock.EnterWriteLock()
xwriter = New XmlTextWriter(xmlfile, Encoding.UTF8)
'other logic
readerWriterLock.ExitWriteLock()
'anything reading from this would need to have the following
readerWriterLock.EnterReadLock()
'logic
readerWriterLock.ExitReadLock()
Try this and then if not successful post the exception message and any other information that you can.