I have a VB.NET application that I use to load various files into a RichTextBox and then scan through the document to find specific words. It's similar to the Find function in Word. The app was running fine until a 5,150 line .sql document run through it and it's taking upwards of 10 minutes to run to completion.
Can anyone recommend a better way of coding it than I have below?
If sqlText.Contains("GRANT") Then
Dim searchstring As String = "GRANT"
Dim count As New List(Of Integer)()
For i As Integer = 0 To rtbFile.Text.Length - 1
If rtbFile.Text.IndexOf(searchstring, i) <> -1 Then
count.Add(rtbFile.Text.IndexOf(searchstring, i))
End If
Next
Try
For i As Integer = 0 To count.Count - 1
rtbFile.Select(count(i), searchstring.Length)
rtbFile.SelectionBackColor = Color.Yellow
rtbFile.SelectionFont = New Font(rtbFile.Font, FontStyle.Bold)
count.RemoveAt(i)
Next
Catch ex As Exception
End Try
rtbFile.Select(rtbFile.Text.Length, 0)
rtbFile.SelectionBackColor = Color.White
rtbFile.SelectionFont = New Font(rtbFile.Font, FontStyle.Regular)
End If
That first loop is killing the performance, you are calling IndexOf for every character in the string. Also the two loops can be merged in to one. Change it to:
rtbFile.SelectionBackColor = Color.Yellow
rtbFile.SelectionFont = New Font(rtbFile.Font, FontStyle.Bold)
For Each m As Match in Regex.Matches(sertbFile.Text, searchstring)
rtbFile.Select(m.Index, searchstring.Length)
Next
This can also be done with a While loop and RichTextBox.Find():
Dim searchstring As String = "GRANT"
Dim index As Integer = rtbFile.Find(searchstring, 0, RichTextBoxFinds.None)
While index <> -1
rtbFile.Select(index, searchstring.Length)
rtbFile.SelectionBackColor = Color.Yellow
rtbFile.SelectionFont = New Font(rtbFile.Font, FontStyle.Bold)
index = rtbFile.Find(searchstring, index + searchstring.Length, RichTextBoxFinds.None)
End While
You've got a few bad things going on here:
First, the following code:
For i As Integer = 0 To rtbFile.Text.Length - 1
If rtbFile.Text.IndexOf(searchstring, i) <> -1 Then
count.Add(rtbFile.Text.IndexOf(searchstring, i))
End If
Next
This is looping through every character in your string, and calling IndexOf on the entire string from that point forward. So your 50,000-character string is running IndexOf 50,000 times, on large strings.
You only need to call IndexOf as many times as you find a string. When your string is found, you increment your start index to that point, and keep searching only from that point.
Next thing, this code:
For i As Integer = 0 To count.Count - 1
...
count.RemoveAt(i)
Next
The RemoveAt line is unnecessary. You're already looping through a list, so you don't need to remove the items as you go along. The way it stands, your loop will skip every other item in your list.
Whoops. I missed a very important point about the IndexOf (and incorrectly assumed it was fed with the end of the last match). See Magnus's answer.
I am not sure where the bottleneck is (and it might very well be from setting the selection itself), but here are my suggestions, roughly in order of priority:
Invoke rtbFile.Text once to avoid any roundtrips to underlying control (perhaps a native Windows control?) and use a variable to store the resulting string. Once the string is obtained in .NET, just keep using it directly unless/until the text may change. If the control is native then a lot of work may be required to simply "get the text".
Use normal item iteration over the count collection (not indexing) and do not remove from the front-of the List when assigning the selections. Removing from the front of a List is "expensive" in that it must shift all items down internally. Also, removing the element is unneeded here and dubious at best: since the collection being modified is also is being iterated which likely leads to incorrect behavior (skipped items), regardless of performance.
Only call IndexOf once per loop and use a variable to avoid a duplicate search. This likely won't have an overall impact, but it does avoid some "extra" work. IndexOf itself is fine and doesn't need to be replaced.
YMMV.
Related
I am trying to write, in order to export on txt file, information in two listbox with the same number of rows. I have to export them with the following format: Listbox1, Listbox2. In order to do this, I've tried to use the following code:
Using writer = New StreamWriter(SaveFileDialog1.FileName)
For Each o As Object In Form3.ListBox1.Items And Form3.ListBox2.Items
writer.WriteLine(o)
Next
End Using
I'm receiving the following error:
BC30452 Operator 'And' is not defined for types 'ListBox.ObjectCollection' and 'ListBox.ObjectCollection'.
I've also tried to perform three For Each loops, the first for the LB1, the second for the commas and the third for LB2, but I'm having it exported with content on single lines. How could I solve this?
If you use Enumerable.Zip, as suggested in another answer, then you can make the code more succinct by doing away with the explicit loop:
File.WriteAllLines(SaveFileDialog1.FileName,
Form3.ListBox1.
Items.
Cast(Of Object).
Zip(Form3.ListBox2.
Items.
Cast(Of Object),
Function(x1, x2) $"{x1}, {x2}"))
If you didn't use Zip then you can use a loop this way:
Dim items1 = Form3.ListBox1.Items
Dim items2 = Form3.ListBox2.Items
Using writer = New StreamWriter(SaveFileDialog1.FileName)
For i = 0 To Math.Min(items1.Count, items2.Count)
writer.WriteLine($"{items1(i)}, {items2(i)}")
Next
End Using
The Math.Min part is just in case there are different numbers of items in each ListBox. If you know there aren't then you can do away with that and just use one Count. If there might be different counts but you want to output all items then the code would become slightly more complex to handle that.
As the error message says, the syntax you attempted is simply not valid. There's no feature in VB.NET that does that sort of thing.
However, the .NET Framework API does provide a means for something similar, which would probably work in your case. See Enumerable.Zip(). You can use it like this:
Using writer = New StreamWriter(SaveFileDialog1.FileName)
For Each o As String In Form3.ListBox1.Items.Cast(Of Object).Zip(Form3.ListBox2.Items.Cast(Of Object), Function(x1, x2) x1 & ", " & x2)
writer.WriteLine(o)
Next
End Using
Since you said that both list boxes have the same number of items we can use the number of items in the first listbox less one (indexes start at zero) in a For loop.
I used a StringBuilder so the code does not have to throw away and create a new string on each iteration.
I used an interpolated string indicate by the $ preceding the string. This means I can insert variables in braces, right along with literals.
Call .ToString on the StringBuilder to write to the text file.
Private Sub SaveListBoxes()
Dim sb As New StringBuilder
For i = 0 To ListBox1.Items.Count - 1
sb.AppendLine($"{ListBox1.Items(i)}, {ListBox2.Items(i)}")
Next
File.WriteAllText("C:\Users\xxx\Desktop\ListBoxText.txt", sb.ToString)
End Sub
I just started working on vb.net and came across this I want to know what g.mods.count-1 to 0 step-1 mean in vb.net
If rsp.ModCnt > 0 AndAlso g.ModsSpecified Then
For i As Integer = g.Mods.Count - 1 To 0 Step -1
Dim itemKey As String = String.Format("1__{0}", g.Mods(i).Name)
g.Mods.RemoveAt(i)
Next
End If
This bit of code has a few interesting things in it.
The AndAlso is a short-circuit. If rsp.ModCnt > 0 evaluates to False, the second condition will never be evaluated.
The start value of i is g.Mods.Count - 1 and the end value is 0. On each iteration the value of i will decrease by 1.
A simpler version might look like...
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim lst As New List(Of Integer) From {1, 2, 3, 4}
For i = lst.Count - 1 To 0 Step -1
lst.RemoveAt(i)
Next
MessageBox.Show(lst.Count.ToString)
End Sub
On the first iteration, i will be 3, lst.Count -1.
On the next iteration i will be 2 and so on until the last iteration where i will be 0.
If the coder tried to start the loop with zero and go up to the highest index, lst.Count -1 then we would get an Index Out of Range error.
For i = 0 To lst.Count - 1 'The default is Step 1
Try it and see. When we remove the first item from the list at index 0 the next item becomes index 0. Second iteration remove index 1. The length (.Count) of the list is now 2 (two items have been removed), the highest index is 1 but on the next iteration we try to remove index 2 which doesn't exist. This is why we use highest index to lowest index and Step -1.
As a side note the line
Dim itemKey As String = String.Format("1__{0}", g.Mods(i).Name)
is really useless because it is just overwriting the value on each iteration and falls out of scope at the end of the For block.
I believe there is an error in this code unrelated to the question. Because ItemKey is defined locally within the scope of the loop, we can reduce everything down to this single line:
If rsp.ModCnt > 0 AndAlso g.ModsSpecified Then g.Mods.Clear()
As for the question, the code loops over the g.Mods collection backwards. That's what Step -1 means.
The reason to loop backwards, rather than from front to back, is because it removes items as it goes. If it went from front to back, as items were removed the index of all the items following would change, causing you to skip items when i is incremented. Additionally, that could mean trying to read past the end of the collection, if g.Mods.Count is not rechecked.
But, again, from the code we can see, the whole thing could be replaced with simple .Clear().
This is a simple for-loop (MSDN).
A for loop runs a set number of times (or should be run as such).
For i As Integer declares an integer variable with name i for the scope of the loop body.
= g.Mods.Count - 1 assigns the value of g.Mods.Count - 1 to the variable i.
g is likely some class object with Mods as a public property. Count is a Property of Mods. Mods is likely an object of a collection class such as List (MSDN) or another class that implements the Enumerable interface (MSDN).
As per the For-Loop syntax, Step is indicating how the counter variable (that's i) is changed after each iteration. In this case it's decreased by 1 every time. Step can be omited, then Step 1 is implied.
In short this loop goes over the indexes of some Enumerable called Mods backwards.
Some other things not directly concerning the question:
A local variable itemKey is created inside the loop but never used. Unless the call of the Property Name does something (it shouldn't, that'd be bad style), this line can be removed.
The index of enumerables starts at 0, thus the last index is Count - 1
The loop goes backwards because it removes the elements of Mods. But this is slow. You can simply use Clear() on objects whose class implements IEnumerable to delete all elements of the collection.
The entire loop can be removed and replaced with g.Mods.Clear()
In my code,I have now realised I have to use the New Random function, my code was working before with the Randomize and then the numbers but now it comes up with loads of errors and wont even let me run the program. I think it is only a small error but I just need some help to get the final bit going
Heres the code and thanks for any help :)
I cannot get the code to work with the randomly generated number and I have to use the New Random function I cannot use randomize() Does anybody know how to help here is the code.
Dim timestook As Int32 = 1
Dim usersguess As Integer
Dim value = New Random(0 - 19)
Console.WriteLine("You have to guess this number. It is between 1 and 20. Good Luck !")
usersguess = Console.ReadLine()
'keep looping until they get the right value
While usersguess <> value
'now check how it compares to the random value
If usersguess < value Then
timestook = timestook + 1
Console.WriteLine("You're too low. Go higher ")
ElseIf usersguess > value Then
Console.WriteLine("You're too high. Go Lower.")
timestook = timestook + 1
End If
'If they are wrong the code will run again,after telling the user if they are too high or too low.
usersguess = Console.ReadLine()
End While
' Console.WriteLine("You're correct. Well Done")
If usersguess = value Then
Console.WriteLine("You took,{0}", timestook)
End If
Console.ReadLine()
End Sub
You'll want to do some googling on how to use random numbers. Your problem is that you aren't creating a Random object to handle the random number generation.
Here's how you can fix your code:
Dim randNumGen As New Random() 'Create Random object
Dim value As Integer = randNumGen.Next(0, 20) 'set value equal to a new random number between 0-19
Please note that this code could be further refactored for readability and simplicity (like changing timestook = timestook + 1 to timestook += 1 and selecting better variable names like numberOfGuesses as opposed to timestook, etc.
The expression New Random(0-19) does not do at all what you think it does, name it does NOT return an integer. Instead, it creates an instance of a Random object, which is a type that knows how to create new random values. The 0-19 part of the expression is the seed for the Random object's constructor, and is the same as just passing the value -19.
This looks like it's either homework or personal practice, so I feel like you will be better served in this case with a separate example using the Random type for reference than you would if I fixed the code sample in the question for you:
Dim rnd As New Random()
For i As Integer = 0 To 10
Console.WriteLine(rnd.Next(0, 20))
Next i
It's also worth mentioning here that you typically only want one Random object for your entire program, or at least only one Random object for each logical part of your program. Creating new Random objects resets the seeds, and for best results you want to follow the same seed on subsequent calls to the same instance for a while.
I'm writing an application in VB in which I need to show the user some information which will be copy and pasted into another application however limitations of the other application mean that the string needs to be split into chunks no larger than 55 characters (it's just written notes). I thought the neatest way to do this was to have several textboxes each with a 'copy to clipboard' button to make it convenient for the user.
The code I have is:
Dim invdesc As List(Of String) = Split(splitstring, 55)
txtinvDesc1.Text = invdesc(0)
txtinvDesc2.Text = invdesc(1)
txtinvDesc3.Text = invdesc(2)
...
Split uses a regular expression to return a list of several lines without breaking up words and most of the time this will return a maximum of seven results but occasionally six (my original string max length is 330) and often fewer so my original idea to fill out any strings shorter than 330 with trailing spaces won't work as it's still possible I will either miss text or call a result that isn't there.
Ideally I would just do some kind of loop that only inputs to txtinvDesc(x) while there is data available and ignores the rest (or hides them) but I don't know any way to refer to a textbox other than explicitly or how to put them in any kind of list/array.
So it's a bit of an open question in "how best can I handle this requirement?"
You can create a collection (e.g., Array or List) of TextBox like with any other type/class (as you are doing with String in your code). Sample:
Dim allTextBoxes As New List(Of TextBox)
allTextBoxes.Add(txtinvDesc1)
allTextBoxes.Add(txtinvDesc2)
allTextBoxes.Add(txtinvDesc3)
Alternatively, you might iterate through all the controls in the main form by checking its type (a textbox or not). In that case you would have to set a relationship between the given name of the textbox and the data list index, via other collection for example:
Dim mappingList As New List(Of String)
mappingList.Add("txtinvDesc1")
mappingList.Add("txtinvDesc2")
mappingList.Add("txtinvDesc3")
For Each ctr As Control In Me.Controls
If (TypeOf ctr Is TextBox AndAlso mappingList.Contains(ctr.Name)) Then
ctr.Text = invdesc(mappingList.IndexOf(ctr.Name))
End If
Next
--- CLARIFICATION (not as evident as I thought)
The proposed for each loop relies on a mapping approach, that is, it relates each element in invdesc with the corresponding TextBox name. By definition, both arrays HAVE TO have the same number of elements (otherwise the mapping system wouldn't have made any sense). This is the most efficient and overall-applicable alternative; if the names of the textboxes and invdesc have elements in common (e.g., the numbers), you might just compare the names. BUT WHEN MAPPING YOU HAVE TO ACCOUNT FOR ALL THE ELEMENTS (if there is no associated TextBox to a given item, let the value blank; but all the items have to be accounted).
If you want to index the tbs:
Private TBs as New List (of TextBox)
Early on (after FormLoad) maybe in a FormSetup:
TBs.Add(txtinvDesc1)
TBs.Add(txtinvDesc2)
TBs.Add(txtinvDesc3)
...
Then:
Dim invdesc As List(Of String) = Split(splitstring, 55)
For n As Integer = 0 To invdesc.Count-1
TBs(n).Text = invdesc(n)
Next
' handle the varying 7th TB:
For n As Integer = invdesc.Count-1 To TBs.Count - 1
TBs(n).Enabled = False
TBs(n).Text =""
Next
Or a For/Each:
Dim ndx As Integer = 0
For Each tb As TextBox In TBs
tb.Text = invdesc(ndx)
ndx += 1 ' thanks varo!
Next
Then hide/disable or at least clear the text from any empty ones.
If it turns out there are always 6 you really only need an if statement:
txtinvDesc1.Text = invdesc(0)
txtinvDesc2.Text = invdesc(1)
txtinvDesc3.Text = invdesc(2)
...
If incDesc.Count-1 = 6 Then
txtinvDesc7.Text = invdesc(6)
Else
txtinvDesc7.Enabled= False
txtinvDesc7.Text = ""
End If
I would change the TB names to start at txtinvDesc0.Text to avoid getting confused (as I may have)
Use multiline textbox and in OnKeyPress event force 55 chars per line. You can find subclassed TextBox with that feature in this SO answer :
https://stackoverflow.com/a/17082189/351383
I have a listbox with directories (not local, it is over a network) listed in it.
I am trying to loop through that listbox and remove any empty directories.
However, I noticed that it just skips some empty directories.. I found that if I ran the loop 3 - 5 times it will get them all, but that isn't very efficient.
My Loop:
Dim i As Integer
i = 0
While i < ListBox1.Items.Count
If IO.Directory.GetFiles(ListBox1.Items.Item(i), "*.*").Length = 0 Then
ListBox1.Items.RemoveAt(i)
End If
i = i + 1
End While
So I was just wondering if there is a more efficient way to check the contents of the directory or another way i could achieve this without having to run the loop multiple times.
ListBox1.Items.Count is getting reevaluated every time, making your loop get shorter as time goes on missing some items. A quick solution could be just mark which items you want to remove as you loop.
Dim toRemove As New List(Of ListBoxItem)
For Each item as ListBoxItem in ListBox1.Items
If IO.Directory.GetFiles(item, "*.*").Length = 0 Then
toRemove.Add(item)
End If
Next
For Each item as ListBoxItem in toRemove
ListBox1.Items.Remove(item)
Next
(there is probably a better way, but that's a quick solution off the top of my head)