The question is simple, I have Form1 with a label and some other control. Now in an external class when I call a function I save a setting like this:
My.Setting.Update = Date.Now
this parameter is displayed on the label of Form1 in the Load event, so I want to know how I can refresh the label text when this string is updated. I tried with Form1.Refresh from the other class but didn't worked. Any suggestions?
Create a public sub on Form1 called RefreshFromSettings. This sub should set the label text to the settings value again, just like your code does now in the Load event.
Then in your external class, given a reference to the instance of Form1 in a variable named frm, you can call that sub like this.
frm.RefreshFromSettings()
That will call your code that updated the label text.
Related
I have create a custom component which changes some properties of it's parent form when placed in design time. But I also want this component, in design time again, to add some controls to it's parent form.
I tried something like this code example below, but with no luck. The added control placed on the form, but I can't select it, just stands there!!! Any idea what exactly am I doing wrong?
Public Class MyCustomComponent
Private _MyControl As New MyUserControl
'...Rest of my code
Private Sub OnPlace()
'...Rest of my code
_ParentForm.Controls.Add(_MyControl)
End Sub
Private Sub OnDispose()
'...Rest of my code
_MyControl.Dispose()
End Sub
End Class
First of all, Why are forms classes?
But now on to the main question.
I have:
Form1.vb
Module1.vb
On the form there is a textbox, progress bar, labels etc.
I want to be able to change the properties of these objects on my form from module1, but I cant seem to access them.
These things on the form are objects, right? So do they have a certain scope? and how can I change it?
Wait but according to my solution explorer, these things are properties of a class??
But the form shows up when I run the program?? Wouldn't the form class have to be instantiated so that the form1 object is created?
Not that it matters, but here is a snippet from module1
Sub WriteObjectsToCSV()
Dim props As PropertyInfo() = MyCompanies(1).GetType().GetProperties()
Dim sw As StreamWriter =
My.Computer.FileSystem.OpenTextFileWriter(SaveAs, False)
Dim csv As New CsvHelper.CsvWriter(sw)
csv.WriteHeader(Of Company)()
csv.NextRecord()
For Each company In MyCompanies
'>>> want to write to my text box and change my progress bar here <<<
For Each prop In props
csv.WriteField(prop.GetValue(company))
Next
csv.NextRecord()
Next
End Sub
Forms are classes because they are created dynamically. You can instantiate and open the same form class serveral times and leave the instances open at the same time.
VB automatically instantiates the main form.
You can access the open forms through My.Application.OpenForms. The main form is always the first
Dim mainForm As Form1
mainForm = DirectCast(My.Application.OpenForms(0), Form1)
mainForm.txtOutput.Text = "hello"
To be able to access the controls of the form from outside, they must be declared Public or Internal. You can change the access modifier from the properties window (Modifiers property).
Instead, you can also declare a property in the form to make the text accessible outside
Public Property OutputText() As String
Get
Return txtOutput.Text
End Get
Set(ByVal value As String)
txtOutput.Text = value
End Set
End Property
Now you can write this in the module
mainForm.OutputText = "hello"
I currently have 2 forms. 1 holds user data and is modifiable. The other is a display/read only form.
I am trying to pull data (tbUSI.text) from ReportSettings and pass it to Form1 and display it on my UserData.text control.
I have tried using public properties but to no avail. I would rather use public properties, since its cleaner. Here is the code im using to set the property:
Public Property UserSignedInto As String
Get
Return tbUSI.Text
End Get
Set(value As String)
End Set
End Property
Here is my code attempting to call that property on the main form (form1)
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
UserData.text = UserSignedInto
End Sub
It doesn't pull anything, the textbox on my main form is blank.
Take a look here:
SCCMReports = New ReportSettings
UserData.text = SCCMReports.UserSignedInto
When was the SCCMReports form ever displayed to the user? Since it was never displayed, its tbUSI.Text value will of course be empty because the user never had an opportunity to enter text.
It sounds like you need a reference to an existing instance of ReportSettings, rather than creating a new instance. Where do you have that existing instance?
If Form1 created the instance in another block of code, store it in a class-level member on Form1 (perhaps called SCCMReportsInstance or something of that nature). When the instance is created, set it to the value of that property and reference that property in your code:
UserData.text = Me.SCCMReportsInstance.UserSignedInto
If the ReportSettings form is instead creating the instance of Form1 then it can pass a reference to itself. You'd still have a property on Form1, it would just be set in the constructor. Something like this:
Sub New(ByVal sccmReportsInstance As ReportSettings)
Me.SCCMReportsInstance = sccmReportsInstance
End Sub
So when initializing the Form1 instance, you'd pass the reference:
Dim form1 As Form1
form1 = New Form1(Me)
form1.Show()
Any way you go about it, you need to access the existing instance of the displayed form in order to access its properties. A new instance would have new versions of those properties and wouldn't have the same values.
I know that you can refer to a form "indirectly" by simply including "me" instead of "form1," for example.
Is there a way to do the same thing for form elements like text boxes or radio buttons?
Example:
If me.checked = true then
count += 1
Else
count -=1
End If
The only way to do that is to create a property named checked that wraps a check box control which is a member of your form class. Something like:
Public Property checked() As Boolean
Get
return myCheckbox.Checked
End Get
Set(ByVal Value As Integer)
myCheckbox.Checked = value
End Set
End Property
Doing this doesn't get you much though. It would actually lead to code obfuscation rather than clarity and brevity.
In VB the keyword me is a reference to an instance of the class which contains the scope of code (as a function of that class) which contains the me reference. I don't know if this is clear enough, but basically me can't be used from inside the Form class to refer to a member of the class (such as a CheckBox or RadioButton control) - only to the class itself.
The CheckBox and RadioButton controls that you place on a Form are created as private objects inside of the Form class which contains them. They are called members of the class. From within the class which contains the CheckBox and RadioButton member instances you can refer to the class itself (the Form) as me. So, assuming that you have a checkbox called "checkbox1" as a control on that form, that CheckBox control would be created as a private member inside of the Form like this:
Private checkbox1 as CheckBox
After that, from that form you could refer to that CheckBox like so:
Me.checkbox1
VB.net uses a sender variable that indicates who's action is being sent to the procedure. By adding multiple elements to the procedure's "handles" property you can use the sender to identify the element being active.
When press F5 to compile a project, there are no errors or warnings but the form won't show up. What's up?
Every time that you try to run your code, it starts by creating an instance of frmMain, your default form and the one that is shown at application startup.
When this form is created, it automatically instantiates an instance of Form3 because you instantiate a variable of that type called modifyForm at the top of this form's code file:
Dim modifyForm As New Form3 'modify student
The problem is that, when the runtime goes to instantiate an object of type Form3, it gets called right back to where it was because of this statement at the top of the Form3 code file:
Dim frmMain As New frmMain
Rinse, lather, and repeat. Your code turns into an infinite loop, trying to instantiate an instance of frmMain, which tries to instantiate an instance of Form3, which tries to instantiate an instance of frmMain, ad nauseum. Eventually, this will overflow your available memory and cause a StackOverflowException.
It's important to note that all of this happens before the default instance of frmMain is even shown, because these variables are declared outside of any methods in your code. Because the computer never can escape this infinite loop, it never gets a chance to move on and actually display your form.
And the moment you've all been reading so patiently for:
Fix it by removing the declaration of frmMain at the top of the Form3 code file. I don't know what that's there for, anyway.
EDIT: Hopefully, I can clear up a little confusion regarding passing values between forms. Upon further study of your code, my instincts tell me that the best solution for you is to overload the constructor for Form3 to accept the calling form (the existing instance of frmMain) as an argument. This will allow you to access all of the public members of frmMain from within your Form3 class.
Here's a rough sketch of how you might do this in your code:
Public Class frmMain
''#The private data field that stores the shared data
Private _mySharedData As String = "This is the data I want to share across forms."
''#A public property to expose your shared data
''#that can be accessed by your Form3 object
Public Property MySharedData As String
Get
Return _mySharedData
End Get
Set(ByVal value As String)
_mySharedData = value
End Set
End Property
Private Sub frmMain_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
''#Do all of your other stuff here...
''#Create a new instance of Form3, specifying this form as its caller
Dim otherForm As New Form3(Me)
''#Show the new instance of Form3
otherForm.Show()
End Sub
End Class
Public Class Form3
''#The private field that holds the reference to the main form
''#that you want to be able to access data from
Private myMainForm As frmMain
Public Sub New(ByVal callingForm As frmMain)
InitializeComponent()
''#Save the reference to the calling form so you can use it later
myMainForm = callingForm
End Sub
Private Sub Form3_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
''#Access anything that you need from the main form
MessageBox.Show(myMainForm.MySharedData)
End Sub
End Class
As you can see, frmMain exposes a public property (backed by a correspondingly-named private variable) called MySharedData. This can be absolutely anything you want, and you can have as many of these as you want.
Also notice that how the constructor (the New method) for Form3 accepts an instance of frmMain as an argument. Whenever you create a new Form3 object from frmMain, you just specify Me, which indicates that you want to pass the current instance of frmMain. In the constructor method, Form3 stores that reference to its calling form away, and you can use this reference any time you like in Form3's code to access the public properties exposed by frmMain.
In VS2010 menu, go to Build -> Configuration Manager, does your project have the checkbox in the "Build" column enabled?
If it's project upgraded from an older Visual Studio version it may be that it is not targeting .NET Framework 4.0. In that case you should change it as explained here.
To analyze the problem press F8 (or F10, depends on your default keyboard settings) to step into the code instead of running the app. This should take you to the main method where the main form would be initialized.