I've got a fairly simple question (I think) on passing variables between forms using Visual Basic.
I've got a program with 2 forms (Form1 and Form2). Form1 has 3 radio buttons, which the user has to select one of and then loads Form2.
Now I've made it so that if radiobutton1 is picked, the Public Variable "radio_select" will equal "radiobutton1", if radiobutton2 is picked, "radio_select" will equal "radiobutton2".
But whenever I try call "radio_select" in my second form, it comes up blank. Why could this be? And how can I fix it.
I've tried using if form1.radiobutton1.checked = true but I keep getting the first radiobutton, regardless of the radio button I've selected.
I think the form is being unloaded, or there is an issue somewhere there, as it appears none of the variables get passed to the second form, once it has been initialized. Also note, the first form is hidden Me.Hide() when the second form is called.
Have you considered a slight re-design whereby you create a property on Form2 called RadioSelect and then set this from Form1 before showing Form2:
Class Form2
Public Property RadioSelect As String
...
End Class
...
Dim f2 as new Form2()
f2.RadioSelect = "radiobutton2"
f2.Show() ' Or f2.ShowDialog()
This gets you away from an unnecessary public variable and should also ensure Form2 can see what it needs from Form1, or whoever calls it.
Edit:
The following works for me:
Public Class Form1
Public Test As String
Private Sub Button1_Click(sender As Object, e As System.EventArgs) Handles Button1.Click
Test = "I'm Here"
Me.Hide()
Form2.ShowDialog()
End Sub
End Class
Public Class Form2
Private Sub Form2_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
Text = Form1.Test
End Sub
End Class
Related
The user enters data in Form1 for example his name and phone number, he clicks on the "next" button that opens Form2 and Hide Form1, if he clicks on the "back" button I want the program to show Form1 with the data he entered before
The code for the "Next" Button in Form1:
Private Sub NextButton_Click(sender As Object, e As EventArgs) Handles NextButton.Click
Dim MyForm As New Form2
MyForm.Show()
Me.Hide()
End Sub
What should I do in order to keep the data the user entered if he comes back to Form1?
The code for the "Previous" button in Form2:
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Form1.Show()
Me.Close()
End Sub
One approach you could use is to only the use the DEFAULT INSTANCES of your Forms. These are accessed by using only the name of the Form, WITHOUT ever using the "New" keyword.
You're doing exactly that in Form2 when you show Form1 with:
Form1.Show()
This works because Form1 is your startup object and VB.Net used the default instance to start the application.
You could do the same thing in Form1, to show Form2:
' ... code in Form1 ...
Private Sub NextButton_Click(sender As Object, e As EventArgs) Handles NextButton.Click
Form2.Show() ' show the default instance of Form2 (do NOT use the "new" keyword)
Me.Hide()
End Sub
Just make sure in all places you Hide() the current form instead of closing it.
You can access the properties/fields of the default instances using the same syntax to show them, using only their name. For example, here is a made up value being accessed on Form2:
Dim userName As String = Form2.txtAddress1.Text
This assumes that Form2 was previously displayed and populated by the user. You could access the Forms from anywhere in the code using this type of syntax.
If you want to implement your own "default instance" mechanism, you could use Shared members in a class:
Public Class WizardForms
Public Shared F1 As New Form1
Public Shared F2 As New Form2
Public Shared F3 As New Form3
End Class
Then you could use code like this to display one:
WizardForms.F2.Show()
This would work as long as you are only HIDING the forms. If you allow the user to close the Forms (or close them via code), then you'd need extra code to make sure they get recreated as needed.
I'm trying to pass a value from one form, let's call it Form1 to another form, Form2. When i double click a row in a listview that is in Form2, the value should be passed to a combobox in Form1.
I could get one of my other forms to do this using an event called PropertyChanged, but I can't seem to get it to work on other forms. I don't know if it is the fact that you can only have 1 event in the entire project and not have another with the same name. I'm missing something, but i just don't know where.
This is the code i used in Form2:
Public Event PropertyChanged As Action(Of Object)
Private Sub ListView2_DoubleClick(sender As Object, e as EventArgs) Handles ListView2.DoubleClick
RaiseEvent PropertyChanged(ListView1.SelectedItems(0).SubItems(0).Text)
End Sub
And this is the code I used in Form1:
Dim WithEvents f2 As Form2
Private Sub PropertyChanged(obj As Object) Handles f2.PropertyChanged
cmb_form1.Text = obj
End Sub
There are several ways to implement this. This one is quick and dirty.
It consists of writing up a property in Form2 which is public. When the user makes a choice, it goes in the property. Then Form1 reads the property before it disposes Form2.
Here's a little code snippet to better illustrate what I mean:
Public Class Form1
' This form has a button which opens a Form2 instance
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim form2 As New Form2 ' instantiate Form2
form2.ShowDialog() ' the user chooses a value
MessageBox.Show(form2.Result) ' get it before it's out of scope!
End Sub
End Class
Public Class Form2
Public Property Result As String ' the value is stored in there, it can be any type
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Result = "Clicked!" ' store the value you want to share between forms
Me.Close()
End Sub
End Class
Have fun!
I am getting a an Null reference exception when trying to add an item to a listbox in a different form.
This is my error at run time.
An unhandled exception of type 'System.NullReferenceException'
occurred in ... Additional information: Object reference not set to an
instance of an object.
I am trying to connect the Mainform by initializing it at the top of the class of the secondForm. after I have my data i want to add it to a listbox it the mainform.
Public Class FormHairdresser //The second form
Dim varMainForm As FormMain //connecting the forms ?
Private Sub btnAddHairdresser_Click(sender As Object, e As EventArgs) Handles btnAddHairdresser.Click
hairdresser = HairdresserChoices(HairdresserID) // get the data
varMainForm.lstListBox.Items.Add(hairdresser) //Run time error breaks here.
All i had to to was write the form name instead of ininalised variable.
FormMain.lstListbox.Items.Add("item")
Instead of
Dim varMainForm As FormMain
varMainForm.ListBox.Items.Add("item")
You cannot simply create a new instance of your main form (as has been suggested and expect that to work, you need an actual reference to the mainform that you have created. To help you see the logic involved;
Create a new Winforms project. In the default Form1 add a textbox and a button.
Now add a new form to this application (you can leave it with its default name of Form2. To this form add a TextBox (call it myTextBox) and a button.
Now go back to your first form and doubleclick the button to access the click handler in code. Add the following:
Dim frm as New Form2
frm.Show
Press f5 and click the button and you'll see a new form 2. So far so good.
Now open up the code for Form2 and add the following code so that it ends up looking like this:
Public Class Form2
Private frm As Form1
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
frm.TextBox1.Text = myTextBox.text
End Sub
End Class
build, press f5 and click the button on form1, in the new form2 enter some text in the text box and click the button, you get your null reference exception. The reason you get this is because at the moment the private field frm inForm2 refers to Nothing.
Now open up the code in Form2 and add a constructor and the following code so that it ends up looking like this:
Public Class Form2
Private frm As Form1
Public Sub New(byval frm1 As Form1)
'first we should make sure that we have a parameter to play with
If Not IsNothing(frm1) Then
frm = DirectCast(frm1,Form1)
End If
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
frm.TextBox1.Text = myTextBox.text
End Sub
End Class
Finally go back to your first forms buttonclick handler and change the code slightly so that it looks like this;
Dim frm as New Form2(Me)
frm.Show
Build and run your application, now when you enter text into the textbox in form2 and click the button it will appear in the textbox in Form1.
The reason why this happens is because you have passed an actual reference to the form1 that was originally created when the application started to form2. By casting that reference to your private field used to represent form1 in form2 you can then use it to properly refer to things on form1. This is a very simple concept but one which you need to learn before you will make progress programming.
the Problem is with your initialization of the formmain.with out proper initialization the object you are creating is nothing other than Null.To avoid this we use New Operator.The New operator can often be used to create the instance when you declare it.
So the initialization will look like
Dim varMainForm As New FormMain
Hope this Helps.For more Reference Object Initialization Errors
update:
Dim varMainForm As FormMain //connecting the forms ?
Private Sub btnAddHairdresser_Click(sender As Object, e As EventArgs) Handles btnAddHairdresser.Click
hairdresser = HairdresserChoices(HairdresserID) // get the data
varMainForm = New FormMain
varMainForm.lstListBox.Items.Add(hairdresser) //Run time error breaks here.
Try This.
Public Class FormHairdresser //The second form
Private Sub btnAddHairdresser_Click(sender As Object, e As EventArgs) Handles btnAddHairdresser.Click
Dim varMainForm As FormMain
hairdresser = HairdresserChoices(HairdresserID)
varMainForm.lstListBox.Items.Add(hairdresser)
I have a first Form that is always displayed of way:
Maximized and as content a printscreen of atual screen
Always on top
without borders
and now I want show a second Form on top this first Form, but I haven't success until this moment, in another words, this second Form don't is displayed on top. So how I can do it? All suggestions here are welcome.
Here is how I'm making for show the first Form:
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
For Each s As Screen In Screen.AllScreens
Dim Locker As New Form2(s, 0.3)
Locker.Show()
Next
End Sub
End Class
=========================================================================
Public Class Form2
Public Sub New(ByVal scrn As Screen, ByVal FrmOpacity As Double)
InitializeComponent()
Me.FormBorderStyle = Windows.Forms.FormBorderStyle.None
Me.StartPosition = FormStartPosition.Manual
Me.Bounds = scrn.Bounds
Me.TopMost = True
Me.Opacity = FrmOpacity
Me.ShowInTaskbar = False
Me.BackgroundImageLayout = ImageLayout.None
CaptureScreen(scrn)
End Sub
Private Sub CaptureScreen(ByVal s As Screen)
Using ScreenImg As New Bitmap(s.Bounds.Width, s.Bounds.Height)
Using g As Graphics = Graphics.FromImage(ScreenImg)
g.CopyFromScreen(s.Bounds.Location, Point.Empty, ScreenImg.Size, CopyPixelOperation.SourceCopy)
End Using
Me.BackgroundImage = New Bitmap(ScreenImg)
End Using
End Sub
End Class
You could simply set the Owner of the form2 to be form1
Public Class Form1
.....
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
For Each s As Screen In Screen.AllScreens
Dim Locker As New Form2(s, 0.3)
Locker.Show(Me)
Next
End Sub
.....
End Class
Passing the instance of Form1 to the Show method of Form2 will set the passed instance of the Form1 as the Owner of all the Locker forms that your create in your loop. In this way the Form2 instance will be always above the Form1 instance. Of course, you could remove the setting of the TopMost=True property that could be assigned only to one form at a time (Only one form could be the TopMost)
From MSDN on Owner form property
When a form is owned by another form, it is closed or hidden with the
owner form. For example, consider a form named Form2 that is owned by
a form named Form1. If Form1 is closed or minimized, Form2 is also
closed or hidden. Owned forms are also never displayed behind their
owner form. You can use owned forms for windows such as find and
replace windows, which should not disappear when the owner form is
selected. To determine the forms that are owned by a parent form, use
the OwnedForms property.
What you want is a Modal Dialog. I don't know vb.Net, but in C# .Net if you say
NameOfFormThatShouldBeOnTop.Show();
The form will just show but not necessarily be on top. However, if you go
NameOfFormThatShouldBeOnTop.ShowDialog();
It will be forced on top. From the documentation, it looks like doing this in vb is pretty similar. I would guess it would be something like
NameOfFormThatShouldBeOnTop.ShowDialog()
If I got that syntax wrong, feel free to edit :)
You may try to load a Sub after the LOAD or SHOWN events, that will contain the below code:
private sub LeaveMeAtTop()
Me.Topmost = True
Me.TopLevel = true
Me.Activate()
Me.ResizeRedraw() = true
Me.ResumeLayout()
Me.Focus()
end sub
It will force the form to be displayed at top of all
I have 2 forms in my program. Form1 has a tab control on it, and on one of these tabs there are a load of labels. Form2 has a few textboxes and dropdown lists on it. Form1 has a button on it that opens Form2 on top of it as a normal form, not as a dialog.
There is code in Form1 that on loading populates the labels on it from a MySQL database. This code is in a separate public sub in the form that is called when the form loads.
What I am trying to do is fill in some of the boxes on Form2, when this Form closes it updates the database with these values (Works fine) and then those values are displayed on Form1. I can get Form2 to run the code in Form1 that populates the labels, but the problem is that the labels on Form1 never actually change. I have tried multiple things, including calling refresh on the labels, trying to change the labels from within Form2 instead of Form1, but they just never update. The .text value of the labels is being updated to the new value, I have checked this via debugging and stopping at the correct points to see what the value is.
Any ideas anyone?? I think it might be to do with the fact that it's Form2 calling the code and for some reason it doesn't have access to change the labels on Form1.
Code:
Form1 (AECSurveyForm)
Private Sub AECSurvey_Load(sender As Object, e As EventArgs) Handles MyBase.Load
LoadMeterData()
End Sub
Public Sub LoadMeterData()
Dim AECMeteringDataAdapter As New AECMeteringDataTableAdapter
Dim AECMeteringData As AECMeteringDataDataTable
AECMeteringData = AECMeteringDataAdapter.GetAECMeterDataBySurveyUniqueIdentifier(AECGlobalValues.CurrentSurveyUniqueIdentifier)
'utility
Meter1UtilityLabel.Text = AECMeteringData(0)("Utility1")
End Sub
Private Sub MeterButton1_Click(sender As Object, e As EventArgs) Handles Meter1Button.Click
If Not Application.OpenForms().OfType(Of AECMeteringDataForm).Any Then
AECMeteringDataForm.GetData(AECGlobalValues.CurrentSurveyUniqueIdentifier, 1)
AECMeteringDataForm.Show()
End If
End Sub
Form2 (AECMeteringDataForm)
Private Sub AECMeteringDataForm_FormClosing(sender As Object, e As EventArgs) Handles MyBase.Closing
Dim AECMeteringDataAdapter As New AECMeteringDataTableAdapter
Dim AECMeteringData As AECMeteringDataDataTable
AECMeteringData = AECMeteringDataAdapter.GetAECMeterDataBySurveyUniqueIdentifier(AECGlobalValues.CurrentSurveyUniqueIdentifier)
AECMeteringData(0)("Utility1") = UtilityComboBox.SelectedItem.ToString
AECMeteringDataAdapter.Update(AECMeteringData)
AECSurveyForm.LoadMeterData()
End Sub