I am trying to use a BackgroundWorker to perform tasks on a separate thread.
I am able to pass a single argument to the BackgroundWorker as below:
Send argument to BackgroundWorker:
Private Sub btnPerformTasks_Click(sender As System.Object, e As System.EventArgs) Handles btnPerformTasks.Click
Dim strMyArgument as String = "Test"
BW1.RunWorkerAsync(strMyArgument)
End Sub
Retrieve argument inside BackgroundWorker:
Private Sub BW1_DoWork(sender As System.Object, e As System.ComponentModel.DoWorkEventArgs) Handles BW1.DoWork
Dim strMyValue As String
strMyValue = e.Argument 'Test
End Sub
There are only 2 overloaded methods for RunWorkerAsync(). One that takes no arguments and one that takes one argument.
I want to know:
How can I pass multiple values to BW1.RunWorkerAsync()
How can I retrieve these multiple values from inside BW1_DoWork
You can wrap your arguments in an object and then pass that object to the worker.
To retrieve it, you can just cast e in the DoWork to your custom type.
here's an example:
' Define a class named WorkerArgs with all the values you want to pass to the worker.
Public Class WorkerArgs
Public Something As String
Public SomethingElse As String
End Class
Dim myWrapper As WorkerArgs = New WorkerArgs()
' Fill myWrapper with the values you want to pass
BW1.RunWorkerAsync(myWrapper)
' Retrieve the values
Private Sub bgw1_DoWork(sender As Object, e As DoWorkEventArgs)
' Access variables through e
Dim args As WorkerArgs = e.Argument
' Do something with args
End Sub
Related
I am in a project with multiple form.
I create a TicTacToe form here :
Private Sub MenuTicTacToe(ByVal sender As Object, ByVal e As System.EventArgs)
Dim page As Form = New TicTacToe
page.Show(Me)
End Sub
Here is a TicTacToe form:
Public Class TicTacToe
Public opponent as String
'Some code where user set opponent
Public Function Receive(S As String)
if string = opponent
'Some code
End Function
End Class
I would like to call my function Receive in my main form
If i do:
TicTactoe.Receive(S)
It call a instance of Receive where opponent does not exist.
I would like to find the oppened form of TicTacToe and call Receive
Thanks
Comments in line
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
page.Receive("Joe")
End Sub
'A form level variable to hold a reference to the instance of TicTacToe
'Although vb.net can use default instances, you have created an explicit
'instance of TicTacToe so you need to keep a reference if you want to
'refer to this instance.
Private page As TicTacToe
Private Sub MenuTicTacToe(ByVal sender As Object, ByVal e As System.EventArgs)
page = New TicTacToe()
page.Show(Me)
End Sub
Partial Public Class TicTacToe
Inherits Form
Public opponent As String
'Functions must be declared as a Type
'If you do not need a return value use a Sub
Public Function Receive(S As String) As String
Dim someString As String = ""
If S = opponent Then
'Do something
End If
'There must be a return Value
Return someString
End Function
End Class
Use this to show the form
Dim page As TicTacToe
Private Sub MenuTicTacToe(ByVal sender As Object, ByVal e As System.EventArgs)
page = New TicTacToe
page.Show(Me)
End Sub
Then you can use
page.Receive(S)
Edit
To use multiple forms
For Each f As TicTacToe in Application.OpenForms().OfType(Of TicTacToe)
f.Receive (S)
Next
In C#, you'd need a new instance, but as you are in VB, the compiler already does that for you.
What you are currently doing, is creating a new instance of the TicTacToe form and showing it:
Private Sub MenuTicTacToe(ByVal sender As Object, ByVal e As System.EventArgs)
Dim page As Form = New TicTacToe
page.Show(Me)
End Sub
But you don't save that instance anywhere. Then, in your next piece of code, you are using a different instance, which is the static one created by the compiler:
TicTacToe.Receive(S) // TicTacToe is the static instance
Therefore, you end up calling two different instances, which explains why there is no opponent set.
To get around this problem, do not create a new instance. In your Private Sub MenuTicTacToe, just use the instance created by the compiler, and you won't have this problem, just like this:
Private Sub MenuTicTacToe(ByVal sender As Object, ByVal e As System.EventArgs)
TicTacToe.Show(Me)
End Sub
Hope this helps.
i want to ask something about datagridview in visual basic
i have 1 form name 'form1' and 1 class name 'test' in my project, within the class there is 1 method 'addColumn()'.
i want to add column to datagridview programmatically, when i add directly to form1 from method form1_load, it's success. the code like this
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
DataGridView1.Columns.Add("01", 1)
But when i add the column via method from class test,
Dim obj As test
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
obj.addColumns(DataGridView1)
End Sub
i got error this
"Object reference not set to an instance of an object."
code in class test like this
Public Function addColumns(ByVal dgv As DataGridView)
dgv.Columns.Add("01", 1)
End Function
What wrong with my code?, there are any way to solve this error.
Please help me...
You are not declaring a New test object, hence the error.
Dim obj As New test
Or make the function a Shared Function
Public Shared Function addColumns(ByVal dgv As DataGridView)
dgv.Columns.Add("01", 1)
End Function
Then no need to declare any obj object. Use the function directly.
test.addColumns(DataGridView1)
change Dim obj As test to
Dim obj as New test
You only declared your obj but not initialized. since obj is null when you call addColumns method you will receive
Object reference not set to an instance of an object.
I have a class as seen below:
Public Class parameters
Public Property test As String
Public Property test_type As String
Public Property user_test_name As String
Public Property meas As String
Public Property spec As String
...etc
End Class
I make a list of objects that I import from a csv somewhere. The user_test_name's from the list gets sent to a list box:
For Each parameters In param
' MsgBox(parameters.user_test_name)
ListBox1.Items.Add(parameters.user_test_name)
Next
now when the user selects something from the list i want the rest of the properties of that particular user_test_name object to populate in certain text/combo boxes in the application. Here is how I grab what is selected.
Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged
Dim selected_name As String = ListBox1.SelectedItem()
' MsgBox(selected_name)
find_object_by_user_test_name(selected_name)
End Sub
Now i'm having difficulty finding the object with the selected_name from the list and using its properties to fill the text.combo boxes. I tried the following to no success:
Public Sub find_object_by_user_test_name(ByVal description)
MsgBox(description)
Dim matches = From parameters In param
Where parameters.user_test_name = description
Select parameters
' MsgBox(matches)
' MsgBox(matches.user_test_name)
TextBox1.Text = matches.test
TextBox2.Text = matches.test_name
etc,,, on and on
' populate_area(matches)
End Sub
Instead of adding the name (a string) to the ListBox, add your actual INSTANCE to it.
First, override ToString() in your class so that it displays properly in your ListBox:
Public Class parameters
Public Property test As String
Public Property test_type As String
Public Property user_test_name As String
Public Property meas As String
Public Property spec As String
Public Overrides Function ToString() As String
Return user_test_name
End Function
End Class
Next, add each instance to the ListBox:
For Each parameters In param
ListBox1.Items.Add(parameters)
Next
Now, the SelectedIndexChanged() event, you can cast the SelectedItem() item back to parameters and you already have everything at your disposal:
Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged
If ListBox1.SelectedIndex <> -1 Then
Dim P As parameters = DirectCast(ListBox1.SelectedItem, parameters)
' ... do something with "P" ...
Debug.Print(P.user_test_name & " --> " & P.test)
End If
End Sub
If the user_test_names are unique, it may be easier to use a dictionary and retrieve the objects that way.
Dim params As New Dictionary(Of String, parameters)
params.add(MyParameterObject.user_test_name, MyParameterObject)
Then
Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged
Dim selected_name As String = ListBox1.SelectedItem()
Dim selected_param as parameters = params(selected_name)
End Sub
Something like this should do it:
Public Sub find_object_by_user_test_name(ByVal description As String)
' assuming param is your list of parameter objects
For Each p In param
If p.user_test_name = description Then
TextBox1.Text = p.test
TestBox2.Text = p.test_name
...
Exit For
End If
Next
End Sub
A few notes about your code. First, you can't allow two objects to have the same user_test_name. Second, you can't use parameters as a variable name if you already have a class called parameters in your current namespace (which you do).
There is a simpler solution than any of these--just do the following:
Dim i as Integer = ListBox1.SelectedIndex
Then you can use i as an index to your original list of objects.
In the code below b textbox will contain the string "a.text" what I want b textbox to be the evaluation of the content of the string "a.text" which is the word Test. Please don't suggest:
b.text = a.text
Public Class Form1
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim t As String
a.Text = "Test"
t = "a.text"
b.Text = t
End Sub
End Class
Check out Controls collection of your form. You can find an item based on its name.
Also check out this answer
VB .NET Access a class property by string value
So, you could take your string, split it by the ".", find the control using the Controls Collection, and then get the property using the second half of your string using Reflection.
Of course, if you are just looking for the Text of the textbox, you just need to use the collection and forget the reflection. Like this..
For i As Integer = 1 To 25
.fields("Field" & i).value = Me.Controls("QAR" & i).Text
Next
You can do what you asked for using Reflection ... I'm not an enormous fan of it for something like this, but here's how it would look in your code:
Imports System.Reflection
Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
a.Text = "Hello"
Dim t As String = "a.Text"
b.Text = DirectCast(SetValue(t), String)
End Sub
Public Function SetValue(ByVal name As String) As Object
Dim ctrl As Control = Me.Controls(name.Split("."c)(0))
Return ctrl.GetType().GetProperty(name.Split("."c)(1)).GetValue(ctrl, Nothing)
End Function
End Class
This would set textbox a's value to "Hello" and then copy that to textbox b using the reflection method.
Hope this helps!
Hi
I am using following code to run a private function.
I have two values in my combo box, One and Two and two private functions with the same names, Private Sub One() and Private Sub Two()
I want my application to call the function whatever value user choses in the combo box.
If One is chosen in the combo box, Private function one should be called.
Thanks
Code is below, that does not work
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim vrValue = ComboBox1.Items(1)
Call vrValue()' In this case vrValue is Two, so Two() should be called.
End Sub
Private Sub two()
MsgBox("Function called")
End Sub
Make your subs functions (the only difference is the returning of a value) and put them in their own class:
Public Class RunFunctions
Dim oMessageBox As MessageBox
Public Function One() As String
'oMessageBox = MessageBox
Return "Message One"
End Function
Public Function Two() As String
Return "Message Two"
End Function
End Class
Add Each function from the class as an item in your combo box:
Public Class Combo_Functions
Dim oRunFunction As RunFunctions
Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As Object _
, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
MessageBox.Show(ComboBox1.Items(ComboBox1.SelectedIndex()))
End Sub
Private Sub Combo_Functions_Load(ByVal sender As Object _
, ByVal e As System.EventArgs) Handles Me.Load
oRunFunction = New RunFunctions
ComboBox1.Items.Add(oRunFunction.One())
ComboBox1.Items.Add(oRunFunction.Two())
End Sub
End Class
When the combo box is changed (or use the code for the button click) the messagebox for the correct function is executed.
Dim vrValue = ComboBox1.SelectedItem.ToString()
Select vrValue
Case "One"
One()
Else
Two()
End Select
It looks like what you're trying to do is to dynamically call a particular method using a string variable that contains its name. For example, the combo box would contain items "One" and "Two", and you would call the sub named "One" if the first item in the combo box is selected, or the sub named "Two" if the second item is selected. To that end, you may find this article interesting:
http://www.codeproject.com/KB/cs/CallMethodNameInString.aspx
The code in the article is in C#, which shouldn't be too difficult to convert to VB. But here's the translated version of the code for simply invoking a method without passing or returning any parameters (note: I have not tested this code). It simply uses reflection to find the appropriate method:
Public Shared Sub InvokeStringMethod(ByVal typeName As String, ByVal methodName As String)
'Get the type of the class
Dim calledType As Type = Type.[GetType](typeName)
'Invoke the method itself
calledType.InvokeMember(methodName, BindingFlags.InvokeMethod Or BindingFlags.[Public] Or BindingFlags.[Static], Nothing, Nothing, Nothing)
End Sub
You simply pass the name of the class that contains the method(s) you want to call as the typeName and the name of the method itself that you want to call as the methodName:
InvokeStringMethod("MyClass", "Two")