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Should you unsubscribe from static self events?

I have multiple MacroPanels which are custom UI elements, I wanted that at a given time only a single one could be active (indicating that a macro is loaded to a hotkey), regardless of the current UI window.
internal MacroPanel()
{
InitializeComponent();
MacroPanel.Selected += MacroPanel_Selected;
this.Disposed += MacroPanel_Disposed;
}
private void MacroPanel_Disposed(object? sender, EventArgs e)
{
MacroPanel.Selected -= MacroPanel_Selected;
this.Disposed -= MacroPanel_Disposed;
}
private void MacroPanel_Selected(object? sender, EventArgs e)
{
if (this == sender)
return;
this.BackColor = Color.Yellow;
}
internal void SelectPanel()
{
this.BackColor = Color.Orange;
Selected?.Invoke(this, EventArgs.Empty);
}
I achieved the desired behaviour by having a static event inside the MacroPanel that every Macro panel instance listens to.
I know that subscribing to a static event can cause memory leaks.
The question is should MacroPanel instance unsubscribe from its own static
event after disposal?
Would it cause memory leaks or other issues if
I would not unsubscribe from the Selected event?
Is subscribing to the Disposed event a proper way to achieve this or is ther any other
probably more beneficial way?

Multithreading with events in WPF

UPDATE:
As mentioned in the comments section the problem was solved, but I do not understand why my way of implementation was wrong.
I have this situation:
I have a device which can be triggered with an event in my WPF project.
This event pulls Data from my device at a polling rate of 1ms. I want to process
the data in different threads.
My approach was, to start a backgroundworker which registers the device event (I read events run on the thread they are called from). In the device event itself the data is saved to an object, which is declared in my form. After that the labels in the WPF form a are refreshed with a Invoke Method.
This happens until someone presses cancel on a button in my form, which unregisters the device event and stops the thread.
Here is some code I use:
Declaration in my Main Window:
public partial class MainWindow : Window
{
private BackgroundWorker worker = new BackgroundWorker();
private MeasureObject mObject = new MeasureObject();
... }
This is my initialization:
public MainWindow()
{
InitializeComponent();
this.worker.WorkerSupportsCancellation = true;
this.worker.DoWork += worker_DoWork;
this.worker.RunWorkerCompleted += worker_RunWorkerCompleted;
}
If this button is press i run my background worker:
private void btnStartMeasure_Click(object sender, RoutedEventArgs e)
{
this.worker.RunWorkerAsync();
}
Here I register my event for the device. It should now run on my worker thread. I tried to declare the event itself here too, but it did not work, so I placed it in my main windows.
private void worker_DoWork(object sender, DoWorkEventArgs e)
{
this.myController.ControlCenter.Diagnostics.NewDiagPacketArrived += new EventHandler<NewDiagPacketArrivedEventArgs>(Diagnostics_NewDiagPacketArrived);
// run all background tasks here
}
This is not needed and empty. The worker is only cancelled if the user sets it on cancel.
private void worker_RunWorkerCompleted(object sender,
RunWorkerCompletedEventArgs e)
{
}
This event is triggered in my Window and calls two functions, it should run on the backgroundworker if I am correct.
private void Diagnostics_NewDiagPacketArrived(object sender, NewDiagPacketArrivedEventArgs e)
{
try
{
Measure(e);
this.Dispatcher.BeginInvoke( new Action(() => { SetStates(e); }),System.Windows.Threading.DispatcherPriority.Input);
}
catch
{
}
}
Measure gets the e Object from the device and saves it to a Dataobject i created
private void Measure(NewDiagPacketArrivedEventArgs e)
{
lock(this.mObject)
{
this.mObject.ID = this.list.Count;
....
this.list.Add(this.mObject);
}
}
SetStates refreshed the GUI
private void SetStates(NewDiagPacketArrivedEventArgs e)
{
lock(this.mObject)
{
this.lblID.Content = this.mObject.ID;
}
}
The problem with my code is if I cancel the event and the thread with this code:
private void btnStopMeasure_Click(object sender, RoutedEventArgs e)
{
this.myController.ControlCenter.Diagnostics.NewDiagPacketArrived -= Diagnostics_NewDiagPacketArrived;
this.worker.CancelAsync();
}
And try to get the list where I added my objects, all objects have the same ID's and values. It seems like as soon as I unregister the event or press the stop measure button, all mObjects in my list get overwritten with the mObject at the time when I unregister the event.
so my list looks like this:
list[0].ID = 1
list[1].ID = 1
list[2].ID = 1
rather than this:
list[0].ID = 1
list[1].ID = 2
list[2].ID = 3
Maybe you can help?

Your problem is that you are not creating a new instance of the mObject - you only create one of them here:
private MeasureObject mObject = new MeasureObject();
Your code then adds the SAME object to the list, and updates that. You need to make a new object each time and put it in the list.
this.mObject.ID = this.list.Count;
....
this.list.Add(this.mObject);
Currently your list is a list of the same object.

Avoiding `ObjectDisposedException` while calling `Invoke`

I have 2 forms, one is MainForm and second is DebugForm. The MainForm has a button that sets up and shows the DebugForm like this, And passes a reference to an already opened SerialPort:
private DebugForm DebugForm; //Field
private void menuToolsDebugger_Click(object sender, EventArgs e)
{
if (DebugForm != null)
{
DebugForm.BringToFront();
return;
}
DebugForm = new DebugForm(Connection);
DebugForm.Closed += delegate
{
WindowState = FormWindowState.Normal;
DebugForm = null;
};
DebugForm.Show();
}
In the DebugForm, I append a method to handle the DataReceived event of the serialport connection (in DebugForm's constructor):
public DebugForm(SerialPort connection)
{
InitializeComponent();
Connection = connection;
Connection.DataReceived += Connection_DataReceived;
}
Then in the Connection_DataReceived method, I update a TextBox in the DebugForm, that is using Invoke to do the update:
private void Connection_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
_buffer = Connection.ReadExisting();
Invoke(new EventHandler(AddReceivedPacketToTextBox));
}
But I have a problem. As soon as I close the DebugForm, it throws an ObjectDisposedException on the Invoke(new EventHandler(AddReceivedPacketToTextBox)); Line.
How can I fix this? Any tips/helps are welcome!
UPDATE
I found out if I remove the event in a button event click , and close the form in that button click, everything is fine and my debugform gets closed without any exception...how odd!
private void button1_Click(object sender, EventArgs e)
{
Connection.DataReceived -= Connection_DebugDataReceived;
this.Close();
}

Closing a form disposes of the Form object but cannot forcibly remove references that other classes have to it. When you register your form for events, you are basically giving a reference to your form object to the source of the events (the SerialPort instance in this case).
This means that, even though your form is closed, the event source (your SerialPort object) is still sending events to the form instance and the code to handle these events is still being run. The problem then is that when this code tries to update the disposed form (set its title, update its controls, call Invoke, &c.) you will get this exception.
So what you need to do is ensure that the event gets deregistered when your form closes. This is as simple as detecting that the form is closing and unregister the Connection_DataReceived event handler. Handily you can detect the form is closing by overriding the OnFormClosing method and unregistering the event in there:
protected override OnFormClosing(FormClosingEventArgs args)
{
Connection.DataReceived -= Connection_DataReceived;
}
I would also recommend moving the event registration to an override of the OnLoad method as otherwise it may receive events before the form has been fully constructed which could cause confusing exceptions.

You haven't shown the code for the AddReceivedPacketToTextBox method.
You could try checking for a disposed form in that method:
private void AddReceivedPacketToTextBox(object sender, EventArgs e)
{
if (this.IsDisposed) return;
...
}
Detaching the DataReceived event handler when closing the form is probably a good idea, but isn't sufficient: there is still a race condition which means your AddReceivedPacketToTextBox can be called after the form is closed/disposed. The sequence would be something like:
Worker thread: DataReceived event fired, Connection_DataReceived starts executing
UI thread: Form closed and disposed, DataReceived event detached.
Worker thread: calls Invoke
UI thread: AddReceivedPacketToTextBox executed while form is disposed.
I found out if I remove the event in a button event click , and close the form in that button click, everything is fine and my debugform gets closed without any exception...how odd!
That's not odd. Multithreading bugs ("Heisenbugs") are timing-related and small changes like that can affect the timing. But it's not a robust solution.

The problem could be solved by adding a timer:
bool formClosing = false;
private void Connection_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
if (formClosing) return;
_buffer = Connection.ReadExisting();
Invoke(new EventHandler(AddReceivedPacketToTextBox));
}
protected override void OnFormClosing(FormClosingEventArgs e)
{
base.OnFormClosing(e);
if (formClosing) return;
e.Cancel = true;
Timer tmr = new Timer();
tmr.Tick += Tmr_Tick;
tmr.Start();
formClosing = true;
}
void Tmr_Tick(object sender, EventArgs e)
{
((Timer)sender).Stop();
this.Close();
}
Thanks to JohnWein from MSDN

Trigger control's event programmatically

Assume that I have a WinFoms project. There is just one button (e.g. button1).
The question is: is it possible to trigger the ButtonClicked event via code without really clicking it?

Button controls have a PerformClick() method that you can call.
button1.PerformClick();

The .NET framework uses a pattern where for every event X there is a method protected void OnX(EventArgs e) {} that raises event X. See this Msdn article. To raise an event from outside the declaring class you will have to derive the class and add a public wrapper method. In the case of Button it would look like this:
class MyButton : System.Windows.Forms.Button
{
public void ProgrammaticClick(EventArgs e)
{
base.OnClick(e);
}
}

You can just call the event handler function directly and specify null for the sender and EventArgs.Empty for the arguments.
void ButtonClicked(object sender, EventArgs e)
{
// do stuff
}
// Somewhere else in your code:
button1.Click += new EventHandler(ButtonClicked);
// call the event handler directly:
ButtonClicked(button1, EventArgs.Empty);
Or, rather, you'd move the logic out of the ButtonClicked event into its own function, and then your event handler and the other code you have would in turn call the new function.
void StuffThatHappensOnButtonClick()
{
// do stuff
}
void ButtonClicked(object sender, EventArgs e)
{
StuffThatHappensOnButtonClick();
}
// Somewhere else in your code:
button1.Click += new EventHandler(ButtonClicked);
// Simulate the button click:
StuffThatHappensOnButtonClick();
The latter method has the advantage of letting you separate your business and UI logic. You really should never have any business logic in your control event handlers.

Yes, just call the method the way you would call any other. For example:
private void btnSayHello_Click(object sender, EventArgs e)
{
MessageBox.Show("Hello World!");
}
private void btnTriggerHello_Click(object sender, EventArgs e)
{
btnSayHello_Click(null, null);
}

button1.PerformClick();
But if you have to do something like this maybe it's better to move the code you have under the event on a new method ?

Why don't you just put your event code into a Method. Then have the Event execute the method. This way if you need to execute the same code that the Event rises, you can, but simply just calling the "Method".
void Event_Method()
{
//Put Event code here.
MessageBox.Show("Hello!");
}
void _btnSend_Click(object sender, EventArgs e)
{
Event_Method();
}
void AnotherMethod()
{
Event_Method();
}
Make sense? Now the "Click" event AND anywhere in code you can trigger the same code as the "Click" event.
Don't trigger the event, call the method that the event calls. ;)

In most cases you would not need to do that. Simply wrap your functionality in functions related to a specific purpose (task). You call this function inside your event and anywhere else it's needed.
Overthink your approach.

I recently had this problem where I wanted to programatically click a button that had multiple event handlers assigned to it (think UserControl or derived classes).
For example:
myButton.Click += ButtonClicked1
myButton.Click += ButtonClicked2;
void ButtonClicked1(object sender, EventArgs e)
{
Console.WriteLine("ButtonClicked1");
}
void ButtonClicked2(object sender, EventArgs e)
{
Console.WriteLine("ButtonClicked1");
}
When you click the button, both functions will get called. In the instances where you want to programmatically fire an event handler for a function from a form (for example, when a user presses enter in a Text field then call the InvokeOnClick method passing through the control you. For example
this.InvokeOnClick(myButton, EventArgs.Empty);
Where this is the Form instance you are in.

use a for loop to call the button_click event
private void btnadd_Click(object sender, RoutedEventArgs e)
{
for (int i = 0; i <= 2; i++)
StuffThatHappensOnButtonClick();
}
void StuffThatHappensOnButtonClick()
{
........do stuff
}
we assume at least one time you need click the button

c# trying to get an event to fire when a different window closes

I have one form that has an option to open another (dialogue). I want an event to fire when the second window closes. The first form is named frmMain() the other is frmAddEmployee(). Heres what I have:
in frmMain()
//create and open the second window
public void (object sender, EventArgs e)
{
frmAddEmployee addEmp = new frmAddEmployee();
addEmp.ShowDialogue();
}
//create event to handle addEmp being closed
public void addEmp_Closing(object sender, EventArgs e)
{
PopulateEmployeeList();
}
I'm not sure the event is being recognized as an event. What am I doing wrong?

Events in C# have to be registered manually - the C# compiler will not automatically register method as an event handler based just on the name of the method. You need:
frmAddEmployee addEmp = new frmAddEmployee();
addEmp.Closing += addEmp_Closing; // Register event handler explicitly
addEmp.ShowDialogue();
Automatic registration of events is done in ASP.NET and Visual Basic has Handles clause, but in C#, you need to use the += operator to specify that some method should be called when an event occurs.

Assuming ShowDialogue means ShowDialog, then it shows the form modally and you don't need an event handler:
//create and open the second window
public void (object sender, EventArgs e)
{
frmAddEmployee addEmp = new frmAddEmployee();
addEmp.ShowDialog();
PopulateEmployeeList();
}
If you don't show the second form modally, then you can hook up the event handler before showing the form like this:
public void (object sender, EventArgs e)
{
frmAddEmployee addEmp = new frmAddEmployee();
addEmp.FormClosed += AddEmpClosed;
addEmp.Show();
}
private void AddEmpClosed(object sender, FormClosedEventArgs e)
{
PopluateEmployeeList();
}

There is Closing and Closed events which you can register for on the Form. You are registered for neither, unless your registration is taking place somehwere else?

Before you call addEmp.ShowDialog() you need to set your method to handle the Closing event:
frmAddEmployee addEmp = new frmAddEmployee();
addEmp.Closing += addEmp_Closing;
addEmp.ShowDialogue();