I’m trying to read a stream of data from serial port coming from a digital scale.
If I send the data stream on a textbox I have a correct visualization (except first line)
Stream in textbox
I would like to catch only one row to use this data.
I have try with following code
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim alol As String
alol = SerialPort1.ReadLine
Label1.Text = alol
End Sub
but what append is that every time I click the button, the label, instead of showing the row value "+0000.26kg", take different section of the data stream (EG: "+00" "KG" "000.2" "+0000.26k" ".26kg" and so on.)
Can anyone suggest to me a way to catch this value ?
The string of interest start always with + or - symbol and end with, I guess, a return.
First thing I would check is the parameters on your SerialPort1 control. Make sure the baud rate in particular is set to a value that is supported by your actual serial port.
Related
I am not really sure what went wrong, i declared dt on top as a class variable then declare it as new datatable in fill function used in pageload but when i pressed buttonadd, dt is nothing error pops up.
Private dt As DataTable
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Not Page.IsPostBack Then
fill()
End If
End Sub
Protected Sub fill()
dt = New DataTable
dt.Columns.Add("Status", GetType(String))
End Sub
Protected Sub btnadd_Click(sender As Object, e As EventArgs) Handles btnadd.Click
Dim R As DataRow = dt.NewRow
R("Status") = "Pending"
dt.Rows.Add(R)
'dt.Rows.Add("pending")
GridView1.DataSource = dt
GridView1.DataBind()
End Sub
The key concept is that web pages are "state-less".
That means for each event code stub, then the code is starting over from scratch.
And it means for each browser round trip, then the browser code starts from scratch EACH time. So, you only load up the data table one time (first time - this is GOOD!!!).
The problem of course, without a control on the web page. (say a data grid), or say a simple text box? Those controls survive that so called round trip. The MOST important concept, and if were going to learn ONE thing about asp.net web pages?
You must grasp the round trip concept, and the so called page state.
So, what happens in your case?
First time - page loads - code runs server side (often called code behind).
Your form instance class is created, your load event runs, you load up the table. The browser is THEN send down to the client side. The web page is just sitting here. Maybe you close the browser. Maybe you un-plug your computer. The server does not know, or care about this. In fact, the server does NOT even know the web page exists anymore!!!
So, your web page is sitting here, and you click on that button.
The web page is now sent up to the server, and the code behind starts running - but it STARTS FROM FRESH scratch each time!
So your form level variable called "data table" does NOT exist any more and does NOT have a value.
So, there are several solutions here. For starters, we need that "table" to persist and survive the rounds trip. As noted, most controls you drop into that page WILL keep their values. This is called the "viewstate". So, if we want that data table to survive and "exist" the next time the user does something? Then we need to save or persist that table variable.
Another way? You can use what is called the session(). Session() is a attempt and system to allow use to shove values into Session(). And the session() survives round trips.
Now, given your example?
Well, then our code would become this:
Private dt As DataTable
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Not Page.IsPostBack Then
fill()
Session("MyCoolTable") = dt
else
' this is a page post back - re-load the active table into our
' forms level dt.
dt = Session("MyCoolTable")
end if
In a lot of cases, I would assume the table that drives the grid is a database. And thus I would add the row to the database, and then re-bind the data grid.
But the above use of session() will persist the dt table for you.
I don't normally post on forums because I try to find information for myself, and ask as an absolute last resort. I've tried scouring the net for answers, but I'm only receiving about half of the answer I'm looking for.
I'm currently building an application that deals with state law. There's one combo box and one text box. One for the offense title, and one for the numerical code for that particular code section. So say if I select "Kidnapping", it prepopulates the text box below it with "11-5-77", for example.
The method I've been using for, oh, about the last hour now, is:
If AWOffenseTitle.Text = "Kidnapping" Then
AWCN.Text = "11-5-77"
ElseIf AWOffenseTitle.Text = "False Imprisonment" Then
AWCN.Text = "11-5-78"
With AWOffenseTitle being the combo box name, and AWCN being the text box name. While this has proved to work perfectly well so far, I'm sure you can imagine with hundreds of offense titles, this is going to take a ridiculously long time. Well, I finally found a spreadsheet with offense titles and their respective title codes. What I'm looking to do is create two text files within a folder in the local directory "Offenses". One with a vertical list of offenses, and one with a vertical list of offense code numbers that populate the same lines in each. What I'm looking to do is populate the combo box with the contents of text file one (which I can do already), but then selecting an offense title will read the second text file and display it's proper title code. That's what has me at a loss. I'm relatively well-versed with vb.NET, but I'm not an expert by any means.
I'm hoping someone here will be able to provide a code example and explain it to me line-by-line so I can gain a better understanding. I want to get more proficient with VB although it's not so popular anymore. I've been using VB since 6.0, but not on a regular basis. More on a sporadic project kind of basis.
I really appreciate any assistance anyone might be able to provide, and if you need more information, I'd be glad to answer any questions. I tried to be as thorough as I could.
Thank you in advance!
First, you need to retrieve your data. I demonstrated using an Sql Server database containing a table named Offenses with columns named OffenseTitle and OffenseCode. You will have to change this code to match your situation.
Private Function GetOffenseData() As DataTable
Dim dt As New DataTable
Using cn As New SqlConnection("Your connection string"),
cmd As New SqlCommand("Select OffenseTitle, OffenseCode From Offenses;")
cn.Open()
dt.Load(cmd.ExecuteReader)
End Using
Return dt
End Function
As the Form loads, set the properties of the ComboBox. DisplayMember matches the name of the title column and ValueMember is the name of the code column.
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim dt = GetOffenseData()
ComboBox1.DisplayMember = "OffenseTitle"
ComboBox1.ValueMember = "OffenseCode"
ComboBox1.DataSource = dt
End Sub
Then when the selected item in the combo changes, just set the .Text property of TextBox to the SelectedValue in the combo and your code appears.
Private Sub ComboBox1_SelectionChangeCommitted(sender As Object, e As EventArgs) Handles ComboBox1.SelectionChangeCommitted
TextBox1.Text = ComboBox1.SelectedValue.ToString
End Sub
There are other ways to do this if your data source is other than a database. Please advise if you need additional help.
In addition to HardCode's comment and Mary's detailed answer, I can only add an answer that's somewhere in between them.
It might be the case, that the information is not taken from a database, but from another source, like a text/data file or a web service. So it might be useful to create an abstraction for the data source you actually use.
First, I create a class or struct that will hold the data for each combo box item.
Class Offense
Public ReadOnly Property Title As String
Public ReadOnly Property Code As String
Public Sub New(title As String, code As String)
Me.Title = title
Me.Code = code
End Sub
End Class
Next, you need a method that retrieves a list of offenses that you can bind to your combo box. It's entirely up to you how you fill/fetch the offenses list. I have simply hard coded your two values here.
Private Function GetOffenseData() As List(Of Offense)
Dim offenses As New List(Of Offense)
offenses.Add(New Offense("Kidnapping", "11-5-77"))
offenses.Add(New Offense("False Imprisonment", "11-5-78"))
Return offenses
End Function
At a certain moment (probably in your form's Load event handler), you need to initialize your combo box. Just like Mary did, I use data binding.
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
AWOffenseTitle.DropDownStyle = ComboBoxStyle.DropDownList
AWCN.ReadOnly = True
AWOffenseTitle.DisplayMember = NameOf(Offense.Title)
AWOffenseTitle.ValueMember = NameOf(Offense.Code)
AWOffenseTitle.DataSource = GetOffenseData()
End Sub
Note that I use the NameOf operator to get the desired property names of the Offense class. If you ever decide to rename the properties of your Offense class, you will be able to easily detect where they are used, since the compiler will complain if your code still uses the wrong property names somewhere.
Finally, the app needs to react to combo box value changes, so that the text box will show the corresponding offense code. Mary used an event handler for the SelectionChangeCommitted event, but I use a handler for the SelectedIndexChanged event instead:
Private Sub AWOffenseTitle_SelectedIndexChanged(sender As Object, e As EventArgs) Handles AWOffenseTitle.SelectedIndexChanged
AWCN.Text = AWOffenseTitle.SelectedValue
End Sub
(Up to now, I was not aware of the SelectionChangeCommitted event of the ComboBox control. I will need to look into this event to see if it is actually a better choice for this scenario, but I found that the SelectedIndexChanged event does the job just fine, so for now I sticked with that event, since I am more familiar with it.)
I'm trying to format two specific text boxes to show up as Sq. ft. (txt.Squareft.Text) and US currency (txtTotalprice.Text) after a calculation has been made in Visual Studio 2019 as a Windows Form Application and using visual basic code. I am using .NET framework v4.7.2 and utilizing Windows 10. The way it runs now, the numbers that show up in the textboxes are just numbers without the added Sq. ft. at the end and no currency formatting. I will also add that I am very new to VB and programming in general. Any help or suggestions?
Option Explicit On
Option Infer Off
Public Class Form1
Private Sub btnCalculate_Click(sender As Object, e As EventArgs) Handles btnCalculate.Click
'Variables
Dim decTotalprice As Decimal
Dim decLength As Decimal
Dim decWidth As Decimal
Dim decPrice As Decimal
Dim decSquareft As Decimal
Decimal.TryParse(txtLength.Text, decLength)
Decimal.TryParse(txtWidth.Text, decWidth)
Decimal.TryParse(txtPrice.Text, decPrice)
Decimal.TryParse(txtSquareft.Text, decSquareft)
txtTotalprice.Text = decTotalprice.ToString("C2")
txtSquareft.Text = decSquareft.ToString("N2") & " Sq. ft."
' Calculate the square feet and total price
txtSquareft.Text = txtLength.Text * txtWidth.Text
txtTotalprice.Text = txtPrice.Text * txtSquareft.Text
End Sub
Private Sub btnClear_Click(sender As Object, e As EventArgs) Handles btnClear.Click
' Clears all the text fields with button click
txtLength.Clear()
txtWidth.Clear()
txtPrice.Clear()
txtSquareft.Clear()
txtTotalprice.Clear()
End Sub
Private Sub btnExit_Click(sender As Object, e As EventArgs) Handles btnExit.Click
' Exits the form
Me.Close()
End Sub
End Class
There are two primary issues here and I feel like I bring them up at least ten times a day. Firstly, you are trying to write code without knowing what that code has to do. You've considered the end result but not the steps to get there. If you had done that then it would be obvious that your code doesn't what it's supposed to. Secondly, you clearly haven't debugged your code, which is the first thing anyone should do when they don't get the expected result. That would also let you see that your code doesn't make sense IF you considered what each line is supposed to be doing as it does it.
If this was a manual task, you would get the input from the user, perform the calculation, then display the result. Is that what you're doing here? No, it is not. First you get the user input. That's a start, but you're doing it wrong. As it stands, you would end with zero for any invalid input but you're just ignoring that. The next thing you do is display the formatted output that you haven't even calculated yet. If you had debugged, you'd have seen that both decTotalprice and decSquareft are zero at that point. You finally do the calculations, but with the raw text input instead of the numbers you already parsed, and then you display the results unformatted. You've even got a comment in your code that says that you're doing the calculation AFTER you've displayed the formatted output.
Stop writing code and think about what the required steps are to get to your desired result. Parse the user input, perform the calculations with the numeric data and not the unparsed text, then display those results with formatting. Once you have a clear idea of what you have to do AND tested that manually, then you can write code to implement that algorithm, rather than some vague idea in your head that involves a final result and little else.
You're certainly not the only person who makes these mistakes but they are elementary mistakes. They happen partly because of bad teaching in some cases, but they also happen because everyone wants to jump into the part that is sexy and fun, i.e. writing the code, but they don't want to do the harder but just as important part of considering what the code actually has to do. When they don't get the expected result, they throw their hands up without ever really having tried to fix it. If you haven't tried to understand what the code has to do, you can't have tried to make it do that.
I am a simple beginner and need small help:
I have textbox1 and textbox2.
Supposed when you put a number (for ex. 21) in the textbox1, I need textbox2 to give me the double number (42). I mean that I need textbox2.text=2*textbox1.text
I used this simple code :
Private Sub TextBox1_Textlength(ByVal sender As System.Object, ByVal e As System.EventArgs)
Handles TextBox1.TextChanged
TextBox2.Text = 2*TextBox1.Text
The problem is: when I wrote (in textbo1) only one digit everything it's ok, but I could not write two (or more) digits.
How do I make a delay (interval) which allows me to type a number like (1990 for example) before firing textbox1_changed?
TextChanged fires every time you change the content of the textbox. So there is no way to block this behavior. Perhaps you could add a button and move the recalculation on the button click event or better add an event handler for the Validating event.
This event is triggered when you exit from the control and you have also the option to check the input and block the exiting from the TextBox control
Private Sub textBox1_Validating(ByVal sender As Object, _
ByVal e As System.ComponentModel.CancelEventArgs) Handles TextBox1.Validating
Dim v as Integer
if Not Int32.TryParse(TextBox1.Text, v) Then
e.Cancel = True
MessageBox.Show("Please type a valid number")
Else
TextBox2.Text = (v * 2).ToString
End If
End Sub
Notice that when you handle the user input expecting a numeric value you should apply particular attention because you don't know what the user types. In this case the Int32.TryParse seems to be the appropriate approach.
Another suggestion is to enable immediately the Option Strict ON in your project, the default is OFF and this allows very dangerous code like treating a string like it was a number.
You don't need to. Just allow the TextChanged event to fire every time, and the second text box will always display twice the value of the first one, so when 1 is entered, it will show 2, when the 9 is added, it will show 38, and so on. You should of course address Steve's concerns about validation, and implied type conversions.
My program is already working fine, I use a TextBox to capture the barcode scanner input. The purpose of my program is for time and attendance monitoring, the problem is I want to prevent users from using the keyboard to type in their ID's as it would render the barcode scanner and their ID's with barcodes useless.
*I already tried removing the keyboard from the computer and it did work, but the keyboard must not be removed as a requirement...
Option 1:
Get a barcode-scanner that is connected to a serial-port (raw serial device read by a COM port). As most barcode-scanners emulate keyboard strokes there is no way to directly distinguish a barcode scanner input from a keyboard input (see next option) without going low-level (see last update).
One connected to a serial port (or emulated one via USB as serial-ports are not so common anymore) gives you full control on where the input comes from.
Option 2:
Count number of chars typed by time. Barcode-scanners inject a sequence (line) pretty fast compared to typing. Measuring the time used in the textbox by counting key-presses (use CR+LF as a measure point as these are sent by the scanner as well) can give you one method to distinguish if a human is typing (unless there is one typing fast as f) or the content was injected. If timed-out just reject/clear the input.
In addition the checksum of the barcode (if you use one that contains that) can be used to do an extra validation in addition to time measurement.
(you can detect pasting by overriding the ctrl + v as in the next option).
Option 3:
Combine option 2 but instead of measure in the textbox tap into the ProcessCmdKey() function (by overriding it) and measure there if textbox has focus. This way you can first buffer input, measure time and if within a set time-out value, inject the line into the textbox.
Update:
Option 4: a non-technical approach -
Usability improvements: make it visually very clear that bar-codes must be entered with a scanner and not typed. I am including as an option as it is simple and if made correct also effective (there's no right answer of what is correct unfortunately).
Approached could include f.ex. a watermark in the textbox ("Don't type, scan!" or something in that order). Give it a different color, border, size etc. to distinguish it from normal textboxes, and have a help text associated and available at all time that improves clarity.
I had the same issue and I did the following:
I set an int variable digitsPrevTyped = 0
In the "TextChanged" event of my textbox I added this (the textbox has a maxsize of 17 chars):
Private Sub tbxScannedText_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles tbxScannedText.TextChanged
If tbxScannedText.Text.Length >= 17 Then
SearchFunction(False)
Else
digitsPrevTyped = tbxScannedText.Text.Length
End If
End Sub
Then in my "SearchFunction" I check the following:
Dim inputMethod As Char
If tbxScannedText.TextLength = 17 And digitsPrevTyped = 0 Then
inputMethod = TEXT_SCANNED
Else
inputMethod = TEXT_MANUALLY_ENTERED
End If
If the textbox initially had a length of 0 chars and now has a length of 17 chars it means that the text was scanned. If the length of the previously typed text is less than 17 chars, then the text was typed.
It is very basic but it works for me.
The other possible workaround is to handle keypress event to restrict user input. Do not allow direct input from keyboard and leave the readonly false.
Set following in KeyPress event handler
Private Sub Textbox1_KeyPress(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles Textbox1.KeyPress
e.Handled = True
End Sub
Just disable the keyboard anyway.. when using barcode you can disable the keyboard without using readonly on the textbox..
on keypress event put some code i.e
if e.keychar <> chrw(0) then
e.keychar = chrw(0)
end if
that condition will automatically be trigged when user type anything.. you will forcibly disable any input from user but not from barcode
why not use an "alias" in the bar code like "123##$!" (but make it stupid long) is "JSMITH" and set the font color to the same as the background color in the textbox. The user can't see what they're typing or what the bar code value is when it's scanned.
Super simplistic approach that doesn't really require anything added aside from another field in the the user table.
This is an old post, but it took me some time to figure out a relatively clean way to use a barcode scanner and combobox so this is for future users.
Barcode scanners can often be configured to append carriage return and line feed to the end of the scan. I have a form that can take user input or barcode scanner input into a bound combobox using the _PreviewKeyDown property and trapping on the value "Keys.Enter".
Example:
If ((e.KeyCode = Keys.Enter) Then
'do stuff
Else
'do other stuff
End if
Verifying the data exists in the datasource is a bit trickier because the SelectedValue property of the combobox doesn't update so that event doesn't fire. I used a custom method to verify that the value scanned exists in the datasource. This method uses the .Text property of the combo box. It uses:
Me.combobox.findexactstring(Me.combobox.Text)
If e.KeyCode = Keys.Enter And txt.Text.Length > 0 Then
'To Do
Else
'To Do
End if
All of my scanner input goes into a "hidden" textbox, which then fills the visible ones as needed depending on the input. This, of course, means you need to keep track of where the focus is. Any type of control that can get focus will then make a call in those events to return focus to whatever the "active" textbox is at that time, which is normally the hidden one. For example...
Private Sub buttons_gotFocus(sender As System.Object, e As System.EventArgs) Handles btnPrint.GotFocus, btnInMVPageDown.GotFocus, btnAdv.GotFocus, btnManual.GotFocus, btnResend.GotFocus, dgvInbound.GotFocus, dgvOutbound.GotFocus, TCRole.GotFocus
Try
activeTextbox.Focus()
Catch ex As Exception
'ignore any errors
End Try
End Sub
Most other textboxes are disabled by default, and only enabled under certain conditions. Once that entry is done they are disabled and the hidden one will get focus again. Works like a charm.
There's no need to record previous typed characters.
Here's my solution:
Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged
If TextBox1.Text.Length >= 17 Then '17 or the number of characters your scanner gets.
MsgBox("scanned")
TextBox1.Clear()
Else
If TextBox1.Text.Length <> 0 Then TextBox1.Clear()
End If
End Sub
This answer will handle any fast typing.
Dim scanner_input As Boolean = False
Dim start_typing As DateTime
Private Sub TextBox_part_number_TextChanged(sender As Object, e As EventArgs) Handles
TextBox_part_number.TextChanged
If (TextBox_part_number.Text.Length = 1) Then
start_typing = DateTime.Now
scanner_input = False
'' MsgBox(start_typing.ToString)
ElseIf (TextBox_part_number.Text.Length > 7) Then
If (calc_typing_time(start_typing) < 500) Then
scanner_input = True
Else
scanner_input = False
End If
End If
End Sub
Function calc_typing_time(time_started As DateTime)
Dim time_finished As DateTime
time_finished = DateTime.Now
Dim duration As TimeSpan = time_finished - time_started
Dim time_diff As String = duration.TotalMilliseconds
Return time_diff
End Function
Most of the scanners has a driver to communicate with (Opos) it has functions to open the scanner port and listen to the scanning , so you take the result and decode it in the background and then display the result in the Textbox... what you need to do it to check your barcode scanner's brand go to it's website and download the driver and its manual.
You should just mark your textbox as readonly.