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Exiting application on X button of form pressed

I have a modal form (login) which I want that on closing it using "X" button, force application to exit.
I tried this:
private void Login_Deactivate(object sender, EventArgs e)
{
Application.Exit();
}
this cause my application to exit on pressing login button (closing). but I want exiting only on "X" button of window.
How can I do it?

Get rid of the Deactivate event, you don't need it.
The issue here is that you cannot tell that just the "X" button was pressed. What you really do is track all the other conditions that cause form close, and react when it's not one of those.
You should leverage the DialogResult enum, and allow the calling application to react, instead of trying to do it all in the Login form.
In your Login form constructor, set the property to None:
public Login()
{
DialogResult = DialogResult.None;
}
Then, in your button handler for "OK", set the property: DialogResult = DialogResult.OK.
If you have a specific Cancel event, you can set DialogResult = DialogResult.Cancel.
Ultimately, you could have a FormClosing event in the Login form, in which you can check this value and react. But more importantly, your calling application can check the result from the login form and react there as well.

I think you should use this.Parent.Application.Exit(), it kills whole application.

Instead of Deactivate event, subscribe to the "FormClosing" event of the "Login" form. Write the same code which you have written.
Keep the Deactivate event only if it is required to close the Application when you click outside login form.

Form in C# returns DialogResult.Cancel to Parent When It is Minimized

I have a form "Main" and in Main I am creating another form which I use .ShowDialog() to display it. I do this because I don't want the rest of the code to in Main to execute until after the new form is completed. I am allowing a user to minimize the new form to system tray.
The problem: When the form gets minimized it is returning DialogResult.Cancel to the Main form that called it, causing the next line to run early.
Code to create form from Main form:
for(int i = 0; i < lvAll.SelectedItems.Count; i++)
{
this.Hide();
this.run = new RunProfile(this.profiles[lvAll.SelectedItems[i].Text]);
DialogResult result = run.ShowDialog();
MessageBox.Show(result.ToString());
}
In the new form a user will get a list of files that copy... now the user can continue and copy those files and I would expect to return a result of OK and if not I assume they are going to cancel and return Cancel...
Is my only recourse to return Abort from the new form if a user specifies a cancel and assume that a cancel is someone trying to minimize? This just seems odd

You could handle this in a number of ways, one way is like what follows:
MainTestForm mainTestForm = new MainTestForm();
if (mainTestForm.ShowDialog() != System.Windows.Forms.DialogResult.OK)
{
return;
}
You must set the DialogResult state when you close the form like
this.DialogResult = System.Windows.Forms.DialogResult.OK;
I hope this helps.

This is entirely by design. When you hide a modal dialog, the user doesn't have any way to get back to the program. Dialogs don't have a taskbar button and the rest of the windows in the app are disabled so cannot be activated. The only recourse the user would have is to kill your program with Task Manager.
So Winforms does the logical thing, it automatically closes the dialog to avoid this UI trap. And of course you'll get DialogResult.Cancel.
Use proper UI design, a dialog should always have its MinimizeBox property set to False.

I'm not sure what you are trying to achieve with that. However, to get the Dialog to return anything else, you have to set it in the form's (Dialog's) DialogResult property before the form is closed.
You may also use the Form_Closing event of the dialog to set the DialogResult property to what you want. This is done before the form closes.

Here is a quote from MSDN regarding ShowDialog:
When this method is called, the code following it is not executed
until after the dialog box is closed.
After further reading it does state the X does not close the form but hides it and so you must dispose of it:
When a form is displayed as a modal dialog box, clicking the Close
button (the button with an X in the top-right corner of the form)
causes the form to be hidden and the DialogResult property to be set
to DialogResult.Cancel. The Close method is not automatically called
when the user clicks the Close button of a dialog box or sets the
value of the DialogResult property. Instead, the form is hidden and
can be shown again without creating a new instance of the dialog box.
Because of this behavior, you must call the Dispose method of the form
when the form is no longer needed by your application.
It seems this same issues applies to minimizing a userform as well.

Focus textbox on main form after closing a second form

How do I focus a TextBox element on the main form after closing a second form which is opened by calling ShowDialog()?
I have tried to call MainForm.TextBox.Focus() in the closing and closed event of the second form, but this won't focus the textbox.
I am using System.Windows.Forms on the compact framework.
Thanks.

From your second form, make a button (or another control) return a DialogResult by going into Properties. When you want the second form to close (ie after you press a button) make it return a specific DialogResult. In your main form you can do this:
if(secondform.ShowDialog() == DialogResult.OK)
{
textBox.Focus();
...
}
Calling ShowDialog() will block until it is closed so you could simply do:
secondform.ShowDialog();
textbox.Focus()
However the first example is for when you only want to make the textbox have focus after you press a certain button or do an action on the second form.

ShowDialog means, it's a modal window and the focus won't go back to main form until you close second form. You can set focus back in the same code which you used to open the second form.
SecondFrm.ShowDialog();
Textbox.Focus();

ShowDialog() will only return when the second form is closed, so you can write MyTextBox.Select() right after the call.

SomeForm form1 = new SomeForm();
form1.ShowDialog();
here you're showing the new form.
When you close it, you will execute methods after that, so add
yourTextbox.Focus();
so, its:
SomeForm form1 = new SomeForm();
form1.ShowDialog(); // do what you want in your form, then close it
yourTextbox.Focus();

How to keep the focus back to form when clicking on OK button in windows forms?

I have a windows form with multiple controls and OK and Cancel buttons. In the Click event handler of OK button, it checks to see if there are errors on the form. I need the form to stay open if there are errors. But the code below is not working. If there are errors, it is closing the form and returning to the caller. And I have the below two lines to invoke and show the form.
PtForm paymentForm = new PtForm();
ptForm.ShowDialog();
private void btnOk_Click(object sender, EventArgs e)
{
this.ValidateChildren(ValidationConstraints.Visible);
string ErrorString = GetValidationErrors();
MessageBox.Show(ErrorString, "Errors");
if (!string.IsNullOrEmpty(ErrorString))
{
return;
}
//Processing
}
Thanks for any help.

There's nothing in this code that will close the form. Therefore, the culprit must be outside this code.
Did you set your OK button's DialogResult property to DialogResult.OK? That would explain why the form is closing. AFAIK, if you set DialogResult on the button, that's what happens -- there's no way to veto it in code.
So in that case, you would need to go back to the designer and set the button's DialogResult back to None. Then at the end of your btnOk_Click method, once you've validated all the input and decided that it's safe to close the dialog, add a line that sets your Form's DialogResult property to OK.

Remove DialogResult property of a button-i.e. set it to None.

Closing dialog form closes parent form

I have been dealing with strange problem. I am using KryptonForm in a project. I have a form (say form1) and I need to open another form on a button click from this form. Here is the code:
void btn_click(object sender, EventArgs e)
{
Visible = false;
ShowInTaskbar = false;
var f = new Form2();
f.ShowDialog();
Visible = true;
ShowInTaskbar = true;
}
The problem is that when the Form2 closes it closes the Form1 also. I have tried setting DialogResult = DialogResult.None from Form2 but of no avail. Please help me.
I am always using this technique and this thing has never happened.

Yes, this code is troublesome. It goes wrong when the user closes the dialog. Windows must then find another window to give the focus to. There isn't any left in your app, your main window is invisible. It then picks a window of another app. Odds are good, for example, that this will be a window inside Visual Studio. A big one. Your main form now disappears behind it.
You need to make sure that your main window is visible again before the dialog closes. You can do so by subscribing to the dialog's FormClosing event handler. For example:
private void button1_Click(object sender, EventArgs e) {
using (var dlg = new Form2()) {
dlg.StartPosition = FormStartPosition.Manual;
dlg.Location = this.Location;
dlg.FormClosing += (s, ea) => this.Show(); // <=== Here
this.Hide();
if (dlg.ShowDialog() == DialogResult.OK) {
// etc...
}
}
}

Bugged me for days!! Found this: https://bytes.com/topic/net/answers/769433-c-showdialog-inside-showdialog-closing-both-return
The result was being passed down and I dont know why. But if after the .ShowDialog() I just put this.DialogResult = DialogResult.None, it will fix it. This shouldnt happen in the first place, but this fixes it, so I am not too bothered.
You can also try changing the dialogResult on the button itself to "None" or deleting the this.Btn1.DialogResult... from the designer which worked for some people.
https://social.msdn.microsoft.com/Forums/vstudio/en-US/543093ad-1860-4428-bae1-b0d4f112e04b/showdialog-closes-parent?forum=csharpgeneral

I know this is an old post, but I ran into this, and in my case the accepted answer (at the time I am writing this) is not helpful at all. The answer by #blind Skwirl led me to the culprit.
After 20 years of .Net programming (since it was introduced), I never noticed that BUTTONS have a "dialogresult" property. I always just set the forms "cancelbutton" and "acceptbutton" properties. What I found in my case was that (because I was doing a lot of copy-pasting of buttons), I had a bunch of buttons (not forms) that themselves had their "dialogresult" property set to "cancel", which meant that I would click a button on a dialog that would open another dialog, the "ok" button on the dialog had its result set to "cancel", and the button on the parent form ALSO had its result set to "cancel", so the dialog would close (with a result of cancel) and then the PARENT form would close with a result of cancel, confusing the heck out of me... so...
Just make sure all of your buttons have their dialogresult property set to NONE (or whatever the actual proper setting is that you want).
Bottom line, if a BUTTON (not the form) has its dialogresult property set to anything other than NONE, the form will close with that result when it is clicked (after any click event code has completed).
I hope that helps someone out there.