I have Two Forms
In The First Form I Have A Textbox Called TB1 An A String Called S1
In The Second Form I Have A Label Called L1
I Declared them publicly in a module
Module M1
Public L1 As New Label
Public TB1 As new Textbox
Public S1 As new String
End Module
/../
'in the First form
S1=TextBox1.text
'in the second form
L1.text=S1
But I Get this error "System.NullReferenceException" on the first Label L1
Any ideas why i'm getting this error
Try something like this:
On Form1 in the event calling Form2, Add:
Form2.L1.Text = TextBox1.text
Form2.Show()
You can't put them in a module like that; nothing will see them.
In addition, there's no way to see how this code is flowing.
To do a simple exercise:
Draw first form - form1 with Textbox1 on it.
Make the first form startup form (it will be by default in new winforms project)
Draw 2nd form - form2 with Label1 on it.
Put a button on the first form
Double click the button
In the handler put this code:
Sub Button1_Click (etc...
dim Form2Instance as new Form2
Form2Instance.Label1.Caption = Textbox1.text
Form2Instance.ShowDialog
End Sub
You can put a textbox on form2 and read the results in form1 the same way.
You can tell if the user OK'd (not canceled) form2 like this:
if Form2Instance.ShowDialog() = DialogResults.OK then
' only do this code if they HIT OK
I suggest maybe hitting youtube or pluralsite and watching a 'winforms for beginners' video, if such a thing exists. There are a lot of traps and pitfalls that you will run into hacking away on your own, that will be explained to before hand if you learn the basics. This is especially true if you've only done web programming or are just learning programming.
Related
I am working in Visual Studio creating a Windows Form Application in Visual Studio. I am very new to the language, and am doing a very simple app. I currently have 3 different forms created on one project. I created a button that switches from the first form to the second form. I am not trying to create a button that switches from the second form to the third form, but cannot import the third form into the code of the second project without getting an unnecessary import error.
This is the code for the first form to the second form and this button works
Imports random__Fun_Page_2
Public Class frmMainPage
Private Sub btnStart_Click(sender As Object, e As EventArgs) Handles btnStart.Click
Dim newForm = New frmChoiceOne()
newForm.Show()
Me.Visible = False
End Sub
This is the code from the second form to the third form which gives me the error 'unnecessary import error'
Imports random__Fun_Page_3
Public Class frmChoiceOne
Private Sub radioOneChoiceOne_CheckedChanged(sender As Object, e As EventArgs) Handles radioOneChoiceOne.CheckedChanged
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim newForm2 = New frmChoiceTwo
newForm2.show()
Me.Visible = False
End Sub
End Class
So my question is why can I import the second form on the first project, but cannot import the third form on the second project. Sorry if this does not give clear detail, but if there is any other information I can provide please let me know
As noted, it may well be just a suggestion.
But then again, as a normal course of action one will VERY rare if at all need to use imports for the ability to reference say some other form? That "practice" of using imports for forms is really never required here. It not clear what example or why imports for form names are being used here?
So a general rule, imports are to allow with greater ease to reference or use some .net assembly or library code (by what we call a namespace). As an typical development approach, one does not need nor as a regular development approach do a imports of forms in applications.
So if we have say Form AA and we want to launch form B?
Your code can do this on the click event:
BB.Show()
Me.Hide()
Note that you can (and should) use .show() and .Hide() in palce of .visible.
Now in our form BB, to close the form and return? We could/would use this:
AA.Show()
Me.Close()
Notice how I CLOSED form BB. Note how I did NOT close form AA, since my whole application and startup form was form AA. (if I close form AA, then my whole application shuts down if that is the first "base" form you specify in the project to load on startup. So I did want to close form BB (not just hide it), and then return to form AA.
And in say form BB, there is nothing that prevents you from getting/grabbing controls or values from form AA (or say form CC or whatever).
So no need for "importing" the other
In form BB, you can get/grab/use controls from from AA like this:
Me.TextBox1.Text = AA.TextBox1.Text
So you have full use of any of the loaded forms as per above, and no imports of the forms is or should be required.
So, you would never "import say form AA or CC into that form BB. You have full use of any loaded form and its values etc. in code.
Perhaps you goal is some type of sub-form here? (we don't have that option in vb.net).
But the "general" idea and concept is to not use imports for use of other forms.
If you need some "general" code module for some subs to call (and code not really needed to be part of a form? Then under project, you can add a code module, and place the general subs and functions that are not part of say a form. But once again, no imports should be required to do this.
I will also point out in above, I did not create a "instance" of the form before I used it. Over time one can adopt creating a form instance, but in your general code you can just use the "one line" BB.Show() and the form will load for you - not really a need to "create" the form instance before you use (show) it.
I am building an application using one of our vendors interfaces, which is required to keep a status message box updated.
I have some events which I have handled for testing using a Message box, but now I come to pass these messages to the display box I get nothing.
Public Shared Sub PageAirHandler(ChannelNum As Integer, Index As Integer, ChannelType As CLARITYCOMLib.ChannelType, PageName As String) Handles Status1.AirStatusChanged
MessageBox.Show(PageName)
ControlPanel.AirStatusBox.Text = PageName
End Sub
The messagebox dutifully displays the PageName string, but the textbox does nothing... even if I replace the PageName String variable with "test"
ControlPanel.AirStatusBox.Text = "test"
I get no activity, no errors, nada.
I have googled around, but every example I can find seems to show the same code.
I have recreated the textbox, tried buttons, labels and other objects with the same result.
Setting up a button click handler to update any of these works as expected.
Apologies if this is a noob blunder, but it's driving me nuts!
Using dlg As New Form2
dlg.ShowDialog()
End Using
Things like:
Form2.Show()
Form2.Show(Me)
Form2.ShowDialog()
Form2.ShowDialog(Me)
SHOUL BE AVOIDED but are possible, because Vb.net creates an implicit instance.
But the problem is, this instance gets killed if
the call has be done.
There you can see that a class instance of a project does not interact correctly
in some cases.
As Hans Passant said, your call to set the textbox text
targets the wrong instance.
Invoking to user controls is also possible with:
Me.invoke(sub()
TextBox1.Text = "Blabla"
End sub)
I am working on a project that has WebBrowsers in Other Forms;
I wrote the code below to control these WebBrowsers; but I need the code to recognize (Declare) the WebBrowsers of these forms.
Dim openForm As Form = Nothing
For Index As Integer = My.Application.OpenForms.Count - 1 To 0 Step -1
openForm = My.Application.OpenForms.Item(Index)
If openForm IsNot Me Then
MyWebBrowser.navigate("http://www.google.com/") ' PROBLEM IN THIS LINE
End If
Next
My Module created them as below:
Module MMMBrowser
Dim frmNew As New Form
Dim MekdamBrowser As New WebBrowser
Other info gleaned from comments:
there is form factory of some sort which creates new frmNew
there are many of these open at a time, which is the reason for the backwards loop thru OpenForms to find the last one.
The MekdamBrowser reference is an attempt to refer to the browser on the form.
The easy things is to provide a way for outsiders to tell the form to navigate somewhere using a new Sub, and let the form drive the browser control. This probably eliminates the need for a global MekdamBrowser reference. In the browser form add something like this:
Public Sub GotoNewURL(url As String)
myWebBrowserName.navigate(url)
End Sub
This procedure only exists for Form1 not the generic Form type, so we need to change how you find the form to use. Your existing loop is wonky. It will only ever find the last instance of a form which is not the current form. If you add a third form type, it wont work well:
Dim lastBrowserFrm As Form1 ' use the class name!
' this will try to get the last Instance of Form1
lastBrowserFrm = Application.OpenForms.OfType(Of Form1)().LastOrDefault
' LastOrDefaultcan return nothing if there are none,
' so test
If lastBrowserFrm IsNot Nothing Then
lastBrowserFrm .GotoNewUrl("www.stackoverflow.com")
Else
' create a new one, I guess
End If
Your loop was not considering that there could be other form types in the collection which are not Form1 or even if a new browser form was the last one created! This is more important now because GotoNewURL is only available on Form1 instances.
I changed the name to lastBrowserFrm to reflect what is really going one - it will just find the last one created. If you are trying to work with a specific instance, you need to provide a way to track the ones you create such as with a List(of Form1) or use the Name property so you can tell one from the other. As is, you do not a way to get back a specific form instance.
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In VB, I create 2 forms in 1 project. In form1, I put 3 buttons with different value. In form2, I only put 1 textbox with no value.
My question is, how if I press one of the button in form1, the form2 is automatically opened and the value from the button that I press automatically added to the form2 textbox?
Add following code into your button handler. You can double click button and add the code into event handler which is automatically created:
'Here we are creating actual object and passing string into it constructor method
Dim instanceOfForm2 = new Form2("String value from Form1!")
instanceOfForm2.Show() ' Showing form
In Form2 we need to tweak our constructor to accept one parameter:
Public Sub New(someValue as String)
InitializeComponents() 'This is always first row in form constructor
TextBox1.Text = someValue 'And put that text into textbox...
End Sub
In VB6 you can do all the stuff that lardymonkey has in place, but you don't have to. The most concise way to do what you want is this. First, make your three command buttons in Form1 into a control array. To do this, give them all the same name (I'll use "cmdMyButtons" in my example), and set their index properties to 0, 1, and 2. Then do this in Form1's code window:
Option Explicit
Dim ButtonText(2) As String
Public Sub Form_Load()
ButtonText(0) = "First Button Text"
ButtonText(1) = "Second Button Text"
ButtonText(2) = "Third Button Text"
End Sub
Public Sub cmdMyButtons_Click(Index As Integer)
With Form2
.txtMyTextBox.Text = ButtonText(Index)
.Show vbModal
End With
End Sub
Now, I like lardymonkey's idea of showing modally, so I put it in here as well. However, several things in his code sample aren't intrinsically necessary to do what you want, and create overhead, so I pulled them out:
You don't need to make a property; you can just set the text
directly as I have here.
You don't need to create a form variable; you can just reference the form directly as I have here.
You don't have to load the form explicitly; the form gets
automatically loaded as soon as you set the variable (by the way,
the Show method also automatically loads the form, too--you only use
Load when you want to have the form loaded into memory before you do
anything to it).
If you close the modal form it will be
automatically unloaded. However, unloading a form doesn't set any
object variables referencing it to nothing. Therefore, frmDetail
will not be Nothing when you check it, you will unload a form that
isn't loaded. While this doesn't throw an error (the statement is ignored), I wouldn't do it anyway. So, you don't
need any of the "make sure the form is destroyed" code.
And now, for a short lecture on the whole business of always explicitly destroying object variables:
There is a longstanding argument about whether you need to explicitly set all your local object variables to Nothing before exiting a subroutine in VB6. I don't agree with this at all; VB takes care of this automatically when the variables go out of scope. As far as I can see, the reason that people believe that they have to do this is that the scope finalizer doesn't collect garbage in any particular order, and sometimes two interacting COM objects need to be destroyed in a particular order due to poor coupling architecture. In such a case, you do indeed need to clear the objects in the correct order to work around intermittent bugs, so the myth developed that VB's garbage collection is buggy and needs to be circumvented by always manually destroying object variables.
Frankly, the idea that a programmer is going to always do this and never forget is naive. So I persist in disagreeing with it; the developers of VB6 put a lot more thought and effort into developing the scope finalizer than any programmer is going to put into circumventing it.
Without knowing the specific version of the software you are using we cant answer, we can answer it if you provide the correct version
In .net it's a simple as creating the form then passing the value over.
Friend objForm2 as New Form2
Private Sub button1_Click(ByVal sender As System.Object, ByVal e as System.EventArgs) Handles button1.Click
objForm2 = new Form2()
TextBox1.Text = value
End Sub
This would be a way of doing it in VB6. I've left the error handling up to you.
I've made the assumption that the name of the text box is txtOutput on form2.
In Form2 add the following:
Option Explicit
Public Property Let OutputText(ByVal strOut As String)
txtOutput.Text = strOut
End Property
In Form1 add the following:
Option Explicit
Private Sub Command1_Click()
DisplayForm "1"
End Sub
Private Sub Command2_Click()
DisplayForm "2"
End Sub
Private Sub Command3_Click()
DisplayForm "3"
End Sub
Private Sub DisplayForm(ByVal strValue As String)
'Declare the variables
Dim frmDetail As Form2
'Create the form
Set frmDetail = New Form2
'Load the form and display it modal
Load frmDetail
frmDetail.OutputText = strValue
frmDetail.Show vbModal, Me
'Make sure the form is destoryed
If Not frmDetail Is Nothing Then
Unload frmDetail
Set frmDetail = Nothing
End If
End Sub
Make sure you comment the code and if you need some error handling then add it. If you need help with the VB6 functions you can find it here MSDN VB6 Reference
I have a VBA (Excel 2010) system which involves selecting an item from a listbox and then displaying it in another form. Here is a very simplified version of what happens.
' Part of frmForm1 code module
sub lstListbox_Click
dim MyEvent as string
dim i as integer
i=me.lstListbox.listindex
MyEvent=me.lstlistbox.list(i)
' Now show the item in the second form
Load frmForm2
me.hide
ThisWorkbook.LoadDataIntoForm2 (frmForm2, MyEvent)
frmForm2.show
unload frmForm2
me.show
end sub
The listbox accepts the click, and first the event (the event handler is giver above). Key parts of the event handler are:
Load the second form (to display the detail data)
Pass the second form as a UserForm parameter to a procedure (LoadDataIntoForm2)
Hide the host form (frmForm1) and show the second form (frmForm2)
When the second form processes an Exit click, the code looks like this:
' Part of frmForm2 code module
sub cmdExit_Click
me.hide
end sub
The first time round it works fine - but when I return to frmForm1 (in the tail end of the lstListBox_Click procedure), even though the rest of the form is operative, the listbox remains stubbornly unresponsive.
I've managed to abstract this down to a little demo system if that would help - the same behavior is seen there. (It's regular .xls file, but that seems not to be easily acceptable as an upload)
Has anyone seen this before? And does anyone have any ideas how I might get this to work the way I want it to?
Thanks,
Tony
The default for the .Show method is to make the form modal. Explicitly set it to modeless:
Sub lstListbox_Click
...
Me.Show vbModeless
End Sub