How to prevent or block closing a WinForms window?

Question

How can I prevent window closing by showing a MessageBox? (Technology:WinForms with C#)

When the close event occurs I want the

Answer 1

Catch FormClosing event and set e.Cancel = true

private void AdminFrame_FormClosing(object sender, FormClosingEventArgs e)
{
    var res = MessageBox.Show(this, "You really want to quit?", "Exit",
            MessageBoxButtons.YesNo, MessageBoxIcon.Warning, MessageBoxDefaultButton.Button2);
    if (res != DialogResult.Yes)
    {
      e.Cancel = true;
      return;
    }
}

Answer 2

Within your OnFormClosing event you can show the dialog and if answer is false (to not show) then set the Cancel property of the EventArgs to true.

Answer 3

A special twist might be to always prevent just the user closing the form:

private void Frm_FormClosing(object sender, FormClosingEventArgs e)
{
    e.Cancel = (e.CloseReason == CloseReason.UserClosing); 
    // disable user closing the form, but no one else
}

Answer 4

You can run any code you want when closing the form then, hide the form instead of closing it to prevent it from being disposed

yourFormName.FormClosing += (s, e) =>
{
   // any code you want
   yourFormName.Hide(); // this hides the form
   e.Cancel = true;  // this cancels the close event, you can put any boolean exprission 
};

Answer 5

Straight from MSDN:

private void Form1_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
   // Determine if text has changed in the textbox by comparing to original text. 
   if (textBox1.Text != strMyOriginalText)
   {
      // Display a MsgBox asking the user to save changes or abort. 
      if(MessageBox.Show("Do you want to save changes to your text?", "My Application",
         MessageBoxButtons.YesNo) ==  DialogResult.Yes)
      {
         // Cancel the Closing event from closing the form.
         e.Cancel = true;
         // Call method to save file...
      }
   }
}

In your case you don't need to do anything to explicitly close the form. Unless you cancel it it will close automatically, so your code would be:

private void addFile_FormClosing( object sender, FormClosingEventArgs e ) {
    var closeMsg = MessageBox.Show( "Do you really want to close?", "Warning", MessageBoxButtons.YesNo, MessageBoxIcon.Question );

    if (closeMsg == DialogResult.Yes) {
        // do nothing
    } else {
        e.Cancel = true;
    }
}

Answer 6

private void addFile_FormClosing( object sender, FormClosingEventArgs e ) {
var closeMsg = MessageBox.Show( "Do you really want to close?", "Warning", MessageBoxButtons.YesNo, MessageBoxIcon.Question );

if (closeMsg == DialogResult.Yes) {
    e.Cancel = false;
} else {
    e.Cancel = true;
}

e.Cancel is to enable or disable form closing event. For example, e.Cancel = true will disable you closing.