I know that you should always call dispose on modal forms. However, I have a related question.
If I have a method in my application like
Private Sub tempMethod
Dim expForm as new ExplorerForm(tempDataTable)
expForm.ShowDialog
'Should I call dispose here?
'or would the form be automatically disposed when it goes out of scope
'after this method exits?
End Sub
When the form goes out of scope, it will be garbage collected at some point in the future and Dispose will be called then, but it's better to use the Using keyword in this instance:
Private Sub tempMethod
Using expForm As New ExplorerForm(tempDataTable)
expForm.ShowDialog()
'Other code here
End Using 'Form disposed here
End Sub
Related
I have a simple WinForm application. The main entry point of the application is mainForm. I am using a Timer on the form and the timer interval is being set to 2000ms. The Tick event of the Timer is as below,
Public myValue as Integer = 100
Private Sub myTimer_Tick(sender As Object, e As EventArgs) Handles myTimer.Tick
If myValue = 0 Then
myTimer.Enabled = False
Else
myValue = myValue -1
End If
End Sub
The timer is being called at the start of the application when mainForm is loaded. Now myValue is a global variable and here for the purpose of simplicity I have used this otherwise it is replaced by some process count mechanism which is not required to be explained here.
I am able to use this approach as long as I am using Windows.Forms.Timer placed on some specific Form. I have two more scenarios in which this approach fails.
1 - I have to use the same functionality on some other form and for this currently I am using a separate Timer on another Form and it has its own Tick event.
2 - I have to use the same functionality from another module/class and I am unable to achieve this because for this to work I require a Form.
Now for a start I have looked into Threading.Timer. The problem I am facing is that I don't know how to wait for Threading.Timer to finish as the control goes to next line after Threading.Timer is called. I am not sure whether this can be done with the help of WaitHandle or not. Also I have read that Threading.Timer creates a separate Thread for each of its Tick. This seems like an overkill in my simple scenario.
I just want to use the Timer functionality without the need of Form. Also I could create the similar functionality using a Do Loop with Thread.Sleep inside it but unless I am sure that my Timer functionality is not going to work in other situations I am going to stick to my Timer approach.
I see ... If thats the case, you should really create a second thread that runs a loop. That thread has some exiting parameters that indicates that operation is completed and the Thread itself is set to Isbackground = false.
However, you could also do this ...
Imports System.Timers
Public Class Main
Private Shared WithEvents m_oTimer As Timers.Timer = Nothing
Private Shared m_oWaitHandle_TimerHasCompleted As System.Threading.AutoResetEvent = Nothing
Public Shared Sub Main()
Try
'Application Entry point ...
'Create the global timer
m_oTimer = New Timers.Timer
With m_oTimer
.AutoReset = True
.Interval = 2000
.Start()
End With
'Create the WaitHandle
m_oWaitHandle_TimerHasCompleted = New System.Threading.AutoResetEvent(False)
'Show your form
Dim oFrm As New Form1
Application.Run(oFrm)
'Wait for the timer to also indicate that it has finished before exiting
m_oWaitHandle_TimerHasCompleted.WaitOne()
Catch ex As Exception
'Error Handling here ...
End Try
End Sub
Private Shared Sub m_oTimer_Elapsed(sender As Object, e As ElapsedEventArgs) Handles m_oTimer.Elapsed
'Timer will fire here ...
Try
If 1 = 2 Then
m_oWaitHandle_TimerHasCompleted.Set()
End If
Catch ex As Exception
'Error Handling ...
End Try
End Sub
End Class
Please note that 'm_oWaitHandle_TimerHasCompleted.Set()' will never run, you'll have to add a condition ... however, once run, the WaitOne will complete and the application will exit as required.
Hows zat?
Sounds to me like you want to create a single instance of a timer, that does not need to be instantiated via a form?
If so ... Create a new class called 'Main' and copy the following into it.
Imports System.Timers
Public Class Main
Private Shared WithEvents m_oTimer As Timers.Timer = Nothing
Public Shared Sub Main()
Try
'Application Entry point ...
'Create the global timer
m_oTimer = New Timers.Timer
With m_oTimer
.AutoReset = True
.Interval = 2000
.Start()
End With
'Show your form
Dim oFrm As New Form1
Application.Run(oFrm)
Catch ex As Exception
'Error Handling here ...
End Try
End Sub
Private Shared Sub m_oTimer_Elapsed(sender As Object, e As ElapsedEventArgs) Handles m_oTimer.Elapsed
'Timer will fire here ...
Try
Catch ex As Exception
'Error Handling ...
End Try
End Sub
End Class
Once done, right click on your project and select 'Properties'. In the Application tab you'll see a checkbox called 'Enable Application framework'. Uncheck this box. Now, in the dropdown called 'Startup Object' you should now see 'Sub Main' .... Select that.
When the application runs, Sub Main will now run instead of your form.
This will create the Timer that will fire outside of your form. Please note, as you're not syncing it, I believe it'll run inside a thread so be a little careful there :)
I have been banging my head against the wall all day trying to figure this one out.
I am finishing up a program to simply delete files in specific temp folders. I have read that it is sometimes good practice to create separate classes for methods and variables. So I have created a separate class for a couple methods to delete files and folders in a specified directory. I am using a Background Worker in my Form1 class and am calling my deleteFiles() method from my WebFixProcesses class in the DoWork event in the Form1 class. I am using a Background Worker so that I can easily report progress back to a progress bar on my main form.
The files get deleted without an issue but I just can't get the label on my main form to reflect the current file being deleted. the label doesn't change in any way.
I know the formula is correct as I can get this working if the method is in the Form1 class. and I simply use:
Invoke(Sub()
lblStatus.Text = File.ToString
lblStatus.Refresh()
End Sub)
here is my method that I am calling from the WebFixProcesses class:
Public Shared Sub deleteFiles(ByVal fileLocation As String)
For Each file As String In Directory.GetFiles(fileLocation)
Try
fileDisplay.Add(file)
For i = 1 To fileDisplay.Count
file = fileDisplay(i)
Form1.BackgroundWorker1.ReportProgress(CInt(i / fileDisplay.Count) * 100)
Next
IO.File.Delete(file)
Form1.labelText(file)
Form1.labelRefresh()
Catch ex As Exception
MessageBox.Show(ex.Message)
End Try
Next
End Sub
labelText() and labelRefresh() are methods from my main form which are using delegates to try to pass information to the control:
Public Sub labelText(ByVal file As String)
If lblStatus.InvokeRequired Then
Dim del As New txtBoxDelegate(AddressOf labelText)
Me.Invoke(del, file)
Else
lblStatus.Text = file.ToString()
End If
End Sub
Public Sub labelRefresh()
If lblStatus.InvokeRequired Then
Dim del As New txtBoxRefDelegate(AddressOf labelRefresh)
Me.Invoke(del)
Else
lblStatus.Refresh()
End If
End Sub
If anyone can help me out to inform me what I may be doing wrong it would be immensely appreciated as my head is in a lot of pain from this. And maybe I am going at it all wrong, and just being stubborn keeping my methods in their own class. But any help would be awesome. Thanks guys!
What Hans wrote on the question comment is true: Form1 is a type, not an instance, but to make things easier to newbye programmes (coming from VB6), M$ did a "mix", allowing you to use the form name as the instance of the form in the main thread.
This however works only if you are on that thread.
If you reference Form1 from another thread, a new instance of Form1 is created.
To solve the issue, add this code to the form:
Private Shared _instance As Form1
Public ReadOnly Property Instance As Form1
Get
Return _instance
End Get
End Property
We will use this property to store the current instance of the form. To do so, add this line to the Load event:
Private Sub Form1_Load(sender As Object, e As System.EventArgs) Handles Me.Load
_instance = Me
'other code here
End Sub
Now, from every class, in any thread, if you use
Form1.Instance
...you get the actual form. Now you can Invoke, even from the same form:
Me.instance.Invoke(Sub()
Me.lblStatus.Text = "Hello World"
End Sub)
I have a main form wich is expected to perfom some long operations. In parallel, I'm trying to display the percentage of the executed actions.
So I created a second form like this:
Private Delegate Sub DoubleFunction(ByVal D as Double)
Private Delegate Sub EmptyFunction()
Public Class LoaderClass
Inherits Form
'Some properties here
Public Sub DisplayPercentage(Value as Double)
If Me.InvokeRequired then
dim TempFunction as New DoubleFunction(addressof DisplayPercentage)
Me.Invoke(TempFunction, Value)
Else
Me.PercentageLabel.text = Value
End if
End sub
Public Sub CloseForm()
If Me.InvokeRequired Then
Dim CloseFunction As New EmptyFunction(AddressOf CloseForm)
Me.Invoke(CloseFunction)
Else
Me.Close()
End If
FormClosed = True
End Sub
End class
My main sub, the one which is expected to perform the long operations is in another form as follows:
Private Sub InitApplication
Dim Loader as new LoaderClass
Dim LoaderThread as new thread(Sub()
Loader.ShowDialog()
End sub)
LoaderThread.start()
Loader.DisplayPercentage(1/10)
LoadLocalConfiguration()
Loader.DisplayPercentage(2/10)
ConnectToDataBase()
Loader.DisplayPercentage(3/10)
LoadInterfaceObjects()
Loader.DisplayPercentage(4/10)
LoadClients()
...
Loader.CloseForm()
End sub
The code works almost 95% of the time but sometimes I'm getting a thread exception somewhere in the sub DisplayPercentage. I change absolutely nothing, I just hit the start button again and the debugger continues the execution without any problem.
The exception I get is: Cross-thread operation not valid: Control 'LoaderClass' accessed from a thread other than the thread it was created on event though I'm using : if InvokeRequired
Does anyone know what is wrong with that code please ?
Thank you.
This is a standard threading bug, called a "race condition". The fundamental problem with your code is that the InvokeRequired property can only be accurate after the native window for the dialog is created. The problem is that you don't wait for that. The thread you started needs time to create the dialog. It blows up when InvokeRequired still returns false but a fraction of a second later the window is created and Invoke() now objects loudly against being called on a worker thread.
This requires interlocking, you must use an AutoResetEvent. Call its Set() method in the Load event handler for the dialog. Call its WaitOne() method in InitApplication().
This is not the only problem with this code. Your dialog also doesn't have a Z-order relationship with the rest of the windows in your app. Non-zero odds that it will show behind another window.
And an especially nasty kind of problem caused by the SystemEvents class. Which needs to fire events on the UI thread. It doesn't know what thread is the UI thread, it guesses that the first one that subscribes an event is that UI thread. That turns out very poorly if that's your dialog when it uses, say, a ProgressBar. Which uses SystemEvents to know when to repaint itself. Your program will crash and burn long after the dialog is closed when one of the SystemEvents now is raised on the wrong thread.
Scared you enough? Don't do it. Only display UI on the UI thread, only execute slow non-UI code on worker threads.
Thank you for your proposal. How to do that please ? Where should I
add Invoke ?
Assuming you've opted to leave the "loading" code of the main form in the main UI thread (probably called from the Load() event), AND you've set LoaderClass() as the "Splash screen" in Project --> Properties...
Here is what LoaderClass() would look like:
Public Class LoaderClass
Private Delegate Sub DoubleFunction(ByVal D As Double)
Public Sub DisplayPercentage(Value As Double)
If Me.InvokeRequired Then
Dim TempFunction As New DoubleFunction(AddressOf DisplayPercentage)
Me.Invoke(TempFunction, Value)
Else
Me.PercentageLabel.text = Value
End If
End Sub
End Class
*This is the same as what you had but I moved the delegate into the class.
*Note that you do NOT need the CloseForm() method as the framework will automatically close your splash screen once the main form is completely loaded.
Now, over in the main form, you can grab the displayed instance of the splash screen with My.Application.SplashScreen and cast it back to LoaderClass(). Then simply call your DisplayPercentage() method at the appropriate times with appropriate values:
Public Class Form1
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
InitApplication()
End Sub
Private Sub InitApplication()
Dim Loader As LoaderClass = DirectCast(My.Application.SplashScreen, LoaderClass)
Loader.DisplayPercentage(1 / 10)
LoadLocalConfiguration()
Loader.DisplayPercentage(2 / 10)
ConnectToDataBase()
Loader.DisplayPercentage(3 / 10)
LoadInterfaceObjects()
Loader.DisplayPercentage(4 / 10)
LoadClients()
' Loader.CloseForm() <-- This is no longer needed..."Loader" will be closed automatically!
End Sub
Private Sub LoadLocalConfiguration()
System.Threading.Thread.Sleep(1000) ' simulated "work"
End Sub
Private Sub ConnectToDataBase()
System.Threading.Thread.Sleep(1000) ' simulated "work"
End Sub
Private Sub LoadInterfaceObjects()
System.Threading.Thread.Sleep(1000) ' simulated "work"
End Sub
Private Sub LoadClients()
System.Threading.Thread.Sleep(1000) ' simulated "work"
End Sub
End Class
If all goes well, your splash screen should automatically display, update with progress, then automatically close when your main form has finished loading and displayed itself.
Me.Invoke(TempFunction, Value)
Should be:
Me.Invoke(TempFunction, new Object(){Value})
because the overload with parameters takes an array of parameters.
Value is on the stack of the function in the current thread. You need to allocate memory on the GC heap and copy the value to that memory so that it is available to the other thread even after the local stack has been destroyed.
Running into an odd issue with tasks and delegates. Code in question is running under dotNET 4.5.1, VS2013. On the form's code I have a sub that updates a grid, it checks to see if an invoke is required, and if it is it calls a delegate. When a task runs that's called in the same module, it works as expected, no problems. Threaded or not, the grid updates properly.
However, if the same thing is called from another module, the delegate never gets called and the visual component doesn't get updated. Just a watered down bit of pseudocode to clarify..
In the form's module:
Private Delegate Sub DoWhateverDelegate(ByVal _____)
Public Sub DoWhatever(ByVal _____)
If MyComponent.InvokeReqired
Dim Delegated As New DoWhateverDelegate(AddressOf DoWhatever)
Debug.Print("The delegate fired")
Invoke(Delegated, _____)
Else
' .. carry on as usual ..
End If
End Sub
Elsewhere....
Task.Run(Sub()
' .. various things I'd rather not block the UI thread with ..
DoWhatever()
End Sub)
Works fine. I can do Task.Run__ that calls DoWhatever and it's all happy and good. However if I create a task in another module and call DoWhatever, it doesn't fire the delegate and that visual component doesn't update. The code is identical, in the same module it works, in another module it does not.
I'm probably missing something blatantly obvious.. anyone care to point out my mistake? Thanks.
Edit -- just to clarify, that other module is just code, there's only one form in the entire solution. It's created at program startup automatically, there is no other form creation going on.
Should be a thread-specific issue. Check this:
Public Class Form1
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
foo.DoSomething()
End Sub
End Class
The class with the delegate:
Public Class foo
Public Shared Sub DoSomething()
Task.Run(Sub() UpdateText())
End Sub
Public Delegate Sub UpdateTextDelegate()
Public Shared Sub UpdateText()
Dim f = Form1
'Dim f As Form1 = Application.OpenForms("Form1")
If f.InvokeRequired Then
Dim d As UpdateTextDelegate = AddressOf UpdateText
f.Invoke(d)
Else
f.TextBox1.Text = "Hi"
End If
End Sub
End Class
Run the code and the textbox will not be updated. Use the second f=.... (that one that take a reference from OpenForms) and it will be updated.
If you just try to access the default instance and you are outside the UI-thread, a new instance of the form will be created. That means, the content IS updated, but because that form is not shown, you will not see it.
NOTE I do NOT advise to solve your problem, by using OpenForms. I'd advise to correctly instantiate forms!
Add a new module/class to your code:
Module Startup
Public MyForm1 As Form1
Public Sub main()
MyForm1 = New Form1
Application.Run(MyForm1)
End Sub
End Module
Go to project properties -> application. Disable application framework and choose Sub Main as your start object. In the app, access your form via MyForm1 - or whatever you want to name it. Problem should be gone then.
I'm trying to fix all my project warning according to Microsoft code analysis (CA:XXXXX)
One of the warning is "CA2000: Dispose objects before losing scope"
My Code is:
Private sub Foo()
Dim O As New Form1()
O.Show()
End Sub
Visual studio says that the object O is not disposable, in such situation I can't use the keyword USING because I will lost the object O after End Using:
Private sub Foo()
Using O As New Form1()
O.Show() 'The form will open then close !!!
End Using
End Sub
The form then will open and close
How to get ride with CA2000 in such situation, I don't need to ignore, I want to solve and fix.
Thanks.
I don't need to ignore, I want to solve and fix.
This is, effectively, a false warning, in this specific instance. You don't want to "solve and fix" this message in this specific case, because you want the object to "live" beyond the end of the local scope.
If you call Dispose on the object in that scope, you will (always) close the form, in this case.
How about ShowDialog?
Private sub Foo()
Using O As New Form1()
O.ShowDialog()
End Using
End Sub
It will dispose all resources of Form1 after i has been closed.