I am a beginner and please show me how to pass the parameter object Person to Button.Click event. I'm using vb.net. Here is my code:
Public Class Form1
Public Class MyPersonClass
Public Name As String
Public Age As Integer
Public Title As String
End Class
Public Sub DisplayPerson(ByVal person As MyPersonClass)
Label1.Text = person.Name
Label2.Text = person.Age.ToString()
Label3.Text = person.Title
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
End Sub
End Class
You don’t – Button1_Click is an event handler, you’re not supposed to call it manually. It gets called, with predefined parameters, when a certain event occurs. You cannot really adapt these parameters, simply because it doesn’t make sense: the event would no longer know how to call the handler.
You can easily write your own method and pass any object to it, of course. And you’ve done exactly that with DisplayPerson.
Private ExamplePerson As MyPerson
Private Sub Form_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
ExamplePerson = New MyPersonClass 'thanks Chris Dunaway for the correction
ExamplePerson.Name = "Test Name"
ExamplePerson.Age = 36
ExamplePerson.Title = "Title Name"
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
DisplayPerson(ExamplePerson)
End Sub
Related
I am very new in coding. I can work myself around a working program but this is my first time creating from scratch. Here is my code, yes I know it's probably messy right now.
What I am trying to do sounds simple enough logically.
theory:
This app has multiple buttons when clicked each one will bring up a question. once answered the labels will change to ask another question. so on and so fourth until I run out. This is intended to be a user simple application for step-by-step troubleshooting some test equipment.
I can't seem to figure out why I can't just say if buttonYes=true then blah blah. I don't feel that it is complicated as it seems. I have searched around the forums but I can't seem to find anything like this.
App
Public Class Form1
Class EventHandler
Public Event buttonYes(ByVal Status As String)
Private Sub buttonYes_Click(ByVal sender As Object, ByVal e As EventArgs) Handles buttonYes.Click
RaiseEvent buttonYes("True")
End Sub
End Class
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
buttonYes.Hide()
buttonNo.Hide()
title.Hide()
question.Hide()
action.Hide()
title.Text = ""
question.Text = ""
action.Text = ""
End Sub
Private Sub buttonNo_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles buttonNo.Click
Dim ans As String
ans = "False"
End Sub
Private Sub CompButton(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles compFail.Click
buttonYes.Show()
buttonNo.Show()
title.Show()
question.Show()
action.Show()
title.Text = "Component / SAT"
question.Text = "Are all cables seated properly"
End Sub
Private Sub ComponentFail(ByVal ans)
'Dim ans As String
ans = ""
If ans = "False" Then
action.Text = "Check cable connections and retest"
End If
End Sub
Private Sub buttonYes_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
End Sub
End Class
How to write this code in a right way?
Public Class Form1
Dim y As String = lbl_1.Text
It says:
{A first chance exception of type 'System.NullReferenceException' occurred in calculator.exe}
Can you help me guys?
this is a sample from the code
Public Class Form1
Dim y As String = lbl_1.Text
Private Sub btn_diff_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_diff.Click
lbl_1.Text = y & "-*"
End Sub
Private Sub btn_1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_1.Click
lbl_1.Text = y & "1"
End Sub
Private Sub lbl_1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lbl_1.Click
Dim y As String = lbl_1.Text
lbl_1.Text = y
End Sub
Private Sub btn_n_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_n.Click
lbl_1.Text = ""
lbl_1.Focus()
End Sub
Private Sub btn_2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_2.Click
Dim y As String = lbl_1.Text
lbl_1.Text = y & "2"
End Sub
Private Sub btn_equal_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_equal.Click
lbl_1.Text = Val(lbl_1.Text)
End Sub
End Class
i want to make a calculator
but what should i write in the last button (btn_equal)? i have tried val but it doesnt work as i want
also when i declare y in each conrol it works but in puplic it doesnt work
The controls in the class Form1 need to be initialized before being used. If you want to use a control in that way you need to explicitly add the parameterless constructor to Form1 class
Public Class Form1
Dim y as String
Public Sub New()
' This call is required by the designer.
InitializeComponent()
' Add any initialization after the InitializeComponent() call.
y = lbl_1.Text
....
End Sub
End Class
In your actual code, the reading of the label control's text happens before the label itself has been created in the InitializeComponent hidden call. If you declare explicitly the parameterless constructor (Public Sub New()) then the VS IDE adds the call to the InitializeComponent and you could place the initialization of your string variable after the creation of the label.
(You could find the InitializeComponent method inside the Form1.Designer.vb file if you click Show All Files in the properties window)
For future knowledge consider to read this QA where cases of NullReferenceException are discussed thoroughly.
I would like to know how I should code my VB.net application to react to the form load event in a third-party application (also written in VB.net)
To test, I have created two basic programs, one with two forms (program A) and one (program B) that attempts to the listen to program A's appropriate form load event. I have tried using WithEvents but it does not get fired when Program's A second form loads.
Here is the code for Program A:
Public Class StartPage
Public WithEvents loadtimer As New System.Windows.Forms.Timer
Private Sub StartPage_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
loadtimer.Interval = 1000
loadtimer.Enabled = True
loadtimer.Start()
End Sub
Private Sub loadtimer_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles loadtimer.Tick
loadtimer.Stop()
SystemStatus.Show()
End Sub
End Class
Public Class SystemStatus
Inherits StartPage
Private Sub StartPage_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Me.Label1.Text = "This is the form that I want to listen for the load event"
Me.loadtimer.Enabled = False
End Sub
End Class
Here is the code for Program B:
Imports Program_A
Public Class ListeningForm
Dim WithEvents testlisten As New Program_A.SystemStatus
Private Sub testlisten_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles testlisten.Load
Label1.Text = "SystemStatus form loaded"
End Sub
Private Sub ListeningForm_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Label1.Text = "Waiting for SystemStatus load event..."
End Sub
End Class
I am quite new when it comes to programming so maybe this is not even possible or I just haven't been understanding what I've been reading. In any case please enlighten me as to what my next course of action should be.
Thanks very much in advance,
theoleric
This will do what your asking.
Imports Program_A
Public Class ListeningForm
Dim WithEvents testlisten As New SystemStatus
Private Sub testlisten_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles testlisten.Load
' now this event will fire
Label1.Text = "SystemStatus form loaded"
End Sub
Private Sub ListeningForm_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Label1.Text = "Waiting for SystemStatus load event..."
' the load event will not fire until you call this
testlisten.Show()
End Sub
End Class
i wonder what is wrong with the following vb.net code.
Public Class Form10
Public IDs() As String = TextBox1.Text.Split(",")
Private Sub Form10_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
For Each id In IDs
MsgBox(id)
Next
End Sub
End Class
when i do
Form10.show()
i get an error "Object reference not set to an instance"
You have declared a field in your class to be initialized with a value from a control on the corresponding form that does not yet exist. The control is not initialized and loaded by the time your initializer on your field member is accessed, thus causing the error.
To keep the public IDs declaration, you could remove the initialization from the field declaration, then move the assignment to the Button1_Click event, as follows:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
IDs=TextBox1.Text.Split(",")
' Do something interesting with IDs now...
End Sub
Public Class Form10
Private Sub Form10_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim IDs() As String = TextBox1.Text.Split(",")
Form1.somefunction(IDs)
End Sub
and in Form1
Public Sub somefunction(ByVal IDs() As String)
For Each id In IDs
MsgBox(id)
Next
End Sub
Hey all i am trying to figure out why my 2nd form is not displaying the value i recived in my first form.
The code for the first form is:
Private Sub scannerOnCom_DataReceived(ByVal sender As Object, ByVal e As SerialDataReceivedEventArgs)
responceBack = scannerOnCom.ReadLine
Call frm1110.clickButton(responceBack)
End Sub
The second form code is this:
Public Sub clickButton(ByRef theResponse As String)
txtNumber.Text = theResponse
'Call cmdNextFinish_Click(Nothing, Nothing)
End Sub
However, when i debug it to make sure there is something stored for theResponse, there is but for some reason it does not put it into the textbox. It's blank.
Any help would be great!
David
UPDATE
Ok so Form1:
Dim tmpForm3020 As New frm3020
Private Sub cmd3020_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmd3020.Click
tmpForm3020.Show()
Me.WindowState = FormWindowState.Minimized
End Sub
Private Sub scannerOnCom_DataReceived(ByVal sender As Object, ByVal e As SerialDataReceivedEventArgs)
responceBack = scannerOnCom.ReadLine
tmpForm3020.txtNumber.Text = responceBack
End Sub
If thats correct then i get an error on line:
xForm.txtNumber.Text = responceBack
Saying:
Cross-thread operation not valid: Control 'txtNumber' accessed from a thread other than the thread it was created on.
Are you explicitly creating an instance of your second form, or relying on the default instance? I.e. is "frm1110" the second form's class name, or an instance that you have new'd up? Make sure in either case that it is the same instance that is actually being displayed.
Dim tmpForm3020 As New frm3020
Private Sub cmd3020_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmd3020.Click
tmpForm3020.Show()
Me.WindowState = FormWindowState.Minimized
End Sub
Private Sub scannerOnCom_DataReceived(ByVal sender As Object, ByVal e As SerialDataReceivedEventArgs)
responceBack = scannerOnCom.ReadLine
TestData(responceBack)
End Sub
Private Sub TestData(ByVal xVal As String)
If InvokeRequired Then
Me.Invoke(New MethodInvoker(AddressOf TestData))
' change Me to tmpForm3020 (if it does not work)
' tmpForm3020.Invoke(New MethodInvoker(AddressOf TestData))
Else
tmpForm3020.txtNumber.Text = xVal
End If
End Sub