How do you prevent form closing when events or methods are still running?

Question

I'm struggling with the issue of user prematurely closing (using the Red X button) a form while it is processing an event or another process is calling a method in it. Object references inside the running event or method might become invalid because the close process has been initiated. Is there a simpler approach than adding an isEventOrMethodRunning flag inside all my event handlers or methods, so I can check it and cancel the FormClosing event? It seems hack-ish. Basically, if there is a running form code, prevent the window from closing.

Answer 1

Hi @Joseph Querijero , Welcome to Microsoft Q&A,

You can use the FormClosing event in WinForms to achieve this goal. A more elegant way is to use the FormClosing event to detect whether the user attempts to close the window, and decide whether to allow closing based on the running status of the event or method.

private bool isRunning = false; // Flag indicating whether an event or method is running

private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
if (isRunning)
{
MessageBox.Show("The operation is in progress and the form cannot be closed.");
e.Cancel = true; // Cancel the closing operation
}
}

// Example of a long-running operation
private async void LongRunningOperation()
{
try
{
isRunning = true;
// Simulate a long-running task
await Task.Delay(5000);
}
finally
{
isRunning = false; // Reset the flag after the operation is completed
}
}

Best Regards,

Jiale

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Answer 2

Is there a more elegant way than to litter your code with isRunning flag?

Answer 3

I would use logic in both a cancel button and in closing event were the work is asynchronous and has a cancellation token. This way, if the user cancels you can decide what to do. In the following example the question dialog is asynchronous which works with .NET Core 5 and higher.

Also consider if you disable the red close button a user can still shutdown the application with Task Manager.