[c#] How to know user has clicked "X" or the "Close" button?

In MSDN I found CloseReason.UserClosing to know that the user had decided to close the form but I guess it is the same for both clicking the X button or clicking the close button. So how can I differentiate between these two in my code?

Thanks all.

if (this.DialogResult == DialogResult.Cancel)
        {

        }
        else
        {
            switch (e.CloseReason)
            {
                case CloseReason.UserClosing:
                    e.Cancel = true;
                    break;
            }
        }

if condition will execute when user clicks 'X' or close button on form. The else can be used when user clicks Alt+f4 for any other purpose

I always use a Form Close method in my applications that catches alt + x from my exit Button, alt + f4 or another form closing event was initiated. All my classes have the class name defined as Private string mstrClsTitle = "grmRexcel" in this case, an Exit method that calls the Form Closing Method and a Form Closing Method. I also have a statement for the Form Closing Method - this.FormClosing = My Form Closing Form Closing method name.

The code for this:

namespace Rexcel_II
{
    public partial class frmRexcel : Form
    {
        private string mstrClsTitle = "frmRexcel";

        public frmRexcel()
        {
            InitializeComponent();

            this.FormClosing += frmRexcel_FormClosing;
        }

        /// <summary>
        /// Handles the Button Exit Event executed by the Exit Button Click
        /// or Alt + x
        /// 
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnExit_Click(object sender, EventArgs e)
        {            
            this.Close();        
        }


        /// <summary>
        /// Handles the Form Closing event
        /// 
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void frmRexcel_FormClosing(object sender, FormClosingEventArgs e)
        {

            // ---- If windows is shutting down, 
            // ---- I don't want to hold up the process
            if (e.CloseReason == CloseReason.WindowsShutDown) return;
            {

                // ---- Ok, Windows is not shutting down so
                // ---- either btnExit or Alt + x or Alt + f4 has been clicked or
                // ---- another form closing event was intiated
                //      *)  Confirm user wants to close the application
                switch (MessageBox.Show(this, 
                                    "Are you sure you want to close the Application?",
                                    mstrClsTitle + ".frmRexcel_FormClosing",
                                    MessageBoxButtons.YesNo, MessageBoxIcon.Question))
                {

                    // ---- *)  if No keep the application alive 
                    //----  *)  else close the application
                    case DialogResult.No:
                        e.Cancel = true;
                        break;
                    default:
                        break;
                }
            }
        }
    }
}

namespace Test
{
    public partial class Member : Form
    {
        public Member()
        {
            InitializeComponent();
        }

        private bool xClicked = true;

        private void btnClose_Click(object sender, EventArgs e)
        {
            xClicked = false;
            Close();
        }

        private void Member_FormClosing(object sender, FormClosingEventArgs e)
        {
            if (xClicked)
            {
                // user click the X
            } 
            else 
            {
                // user click the close button
            }
        }
    }
}

It determines when to close the application if a form is closed (if your application is not attached to a specific form).

    private void MyForm_FormClosed(object sender, FormClosedEventArgs e)
    {
        if (Application.OpenForms.Count == 0) Application.Exit();
    }

The CloseReason enumeration you found on MSDN is just for the purpose of checking whether the user closed the app, or it was due to a shutdown, or closed by the task manager, etc...

You can do different actions, according to the reason, like:

void Form_FormClosing(object sender, FormClosingEventArgs e)
{
    if(e.CloseReason == CloseReason.UserClosing)
        // Prompt user to save his data

    if(e.CloseReason == CloseReason.WindowsShutDown)
        // Autosave and clear up ressources
}

But like you guessed, there is no difference between clicking the x button, or rightclicking the taskbar and clicking 'close', or pressing Alt F4, etc. It all ends up in a CloseReason.UserClosing reason.

I also had to register the closing function inside the form's "InitializeComponent()" method:

private void InitializeComponent() {
// ...
this.FormClosing += FrmMain_FormClosing;
// ...
}

My "FormClosing" function looks similar to the given answer (https://stackoverflow.com/a/2683846/3323790):

private void FrmMain_FormClosing(object sender, FormClosingEventArgs e) {
    if (e.CloseReason == CloseReason.UserClosing){
        MessageBox.Show("Closed by User", "UserClosing");
    }

    if (e.CloseReason == CloseReason.WindowsShutDown){
        MessageBox.Show("Closed by Windows shutdown", "WindowsShutDown");
    }
}

One more thing to mention: There is also a "FormClosed" function which occurs after "FormClosing". To use this function, register it as shown below:

this.FormClosed += MainPage_FormClosed;

private void MainPage_FormClosing(object sender, FormClosingEventArgs e)
{
// your code after the form is closed
}

The "X" button registers as DialogResult.Cancel so another option is to evaluate the DialogResult.

If you have multiple buttons on your form, you're probably already associating different DialogResults to each and this will provide you with the means to tell the difference between each button.

(Example: btnSubmit.DialogResult = DialogResult.OK, btnClose.DialogResult = Dialogresult.Abort)

    public Form1()
    {
        InitializeComponent();

        this.FormClosing += Form1_FormClosing;
    }

    /// <summary>
    /// Override the Close Form event
    /// Do something
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    private void Form1_FormClosing(Object sender, FormClosingEventArgs e)
    {
        //In case windows is trying to shut down, don't hold the process up
        if (e.CloseReason == CloseReason.WindowsShutDown) return;

        if (this.DialogResult == DialogResult.Cancel)
        {
            // Assume that X has been clicked and act accordingly.
            // Confirm user wants to close
            switch (MessageBox.Show(this, "Are you sure?", "Do you still want ... ?", MessageBoxButtons.YesNo, MessageBoxIcon.Question))
            {
                //Stay on this form
                case DialogResult.No:
                    e.Cancel = true;
                    break;
                default:
                    break;
            }
        }
    }

You can try adding event handler from design like this: Open form in design view, open properties window or press F4, click event toolbar button to view events on Form object, find FormClosing event in Behavior group, and double click it. Reference: https://social.msdn.microsoft.com/Forums/vstudio/en-US/9bdee708-db4b-4e46-a99c-99726fa25cfb/how-do-i-add-formclosing-event?forum=csharpgeneral

I've done something like this.

private void Form_FormClosing(object sender, FormClosingEventArgs e)
    {
        if ((sender as Form).ActiveControl is Button)
        {
            //CloseButton
        }
        else
        {
            //The X has been clicked
        }
    }

I agree with the DialogResult-Solution as the more straight forward one.

In VB.NET however, typecast is required to get the CloseReason-Property

    Private Sub MyForm_Closing(sender As Object, e As CancelEventArgs) Handles Me.Closing

        Dim eCast As System.Windows.Forms.FormClosingEventArgs
        eCast = TryCast(e, System.Windows.Forms.FormClosingEventArgs)
        If eCast.CloseReason = Windows.Forms.CloseReason.None Then
            MsgBox("Button Pressed")
        Else
            MsgBox("ALT+F4 or [x] or other reason")
        End If

    End Sub

How to detect if the form closed by click on X button or by calling Close() in code?

You cannot rely on close reason of the form closing event args, because if the user click X button on title bar or close the form using Alt + F4 or use system menu to close the form or the form get closed by calling Close() method, all all above cases, the close reason will be Closed by User which is not desired result.

To distinguish if the form closed by X button or by Close method, you can use either of the following options:

• Handle WM_SYSCOMMAND and check for SC_CLOSE and set a flag.
• Check the StackTrace to see if any of the frames contain Close method call.

Example 1 - Handle WM_SYSCOMMAND

public bool ClosedByXButtonOrAltF4 {get; private set;}
private const int SC_CLOSE = 0xF060;
private const int WM_SYSCOMMAND = 0x0112;
protected override void WndProc(ref Message msg)
{
    if (msg.Msg == WM_SYSCOMMAND && msg.WParam.ToInt32() == SC_CLOSE)
        ClosedByXButtonOrAltF4 = true;
    base.WndProc(ref msg);
}
protected override void OnShown(EventArgs e)
{
    ClosedByXButtonOrAltF4 = false;
}   
protected override void OnFormClosing(FormClosingEventArgs e)
{
    if (ClosedByXButtonOrAltF4)
        MessageBox.Show("Closed by X or Alt+F4");
    else
        MessageBox.Show("Closed by calling Close()");
}

Example 2 - Checking StackTrace

protected override void OnFormClosing(FormClosingEventArgs e)
{
    if (new StackTrace().GetFrames().Any(x => x.GetMethod().Name == "Close"))
        MessageBox.Show("Closed by calling Close()");
    else
        MessageBox.Show("Closed by X or Alt+F4");
}