Develop Reference

Is it possible to catch MessageBox closing?

Is there any way for detect MessageBox closing. Some workarounds can be possible maybe I can write my own custom MessageBox, but I want the operating system's MessageBox.
Maybe something like MessageBox.Closing += new EventHandler, any suggestions?

There is no "normal" way of doing that, if not using some not very riliable API calls and sniffing. But according to yuor comment, you need may be something like:
var flag = true;
MessageBox.Show(...);
flag = false;
This is a correct way of doing that. MessageBox.Show(...); is a blocking call.
If you need more control, define your own form, and it wil become your message box.
So you can have full control over it, and have also Closing event handler possibility.

You can use the MessageBox found int Extended WPF Toolkit™ Community Edition.
In its documentation there are two events called
CloseButtonClicked
Closed
But as explained in the Tigran answer, the MessageBox.Show call is modal and block the thread in which you make the call, so there is no need to catch the close event unless you are running another thread that should react immediately in some way to the closing of the messagebox.

In my case I just wanted to see if the MessageBox was clicked and then do something, hope it helps.
DialogResult result = MessageBox.Show("Your message");
if (result == DialogResult.OK)
{
Application.Exit(); //whatever you want
}

Difference between "No" and "Cancel" in MessageBoxButtons

I was using a MessageBox to show a confirmation message when the user goes to delete an item and initially used MessageBoxButtons.YesNoCancel. Later I changed it to YesNo instead because a user pointed out that there was no real difference in "No" and "Cancel" in this case. My question is...what is the difference? Is there ever a reason to use YesNoCancel instead of YesNo?

In your case there is no difference as your question results in just one action and then finishes.
In standard usage, the Yes No Cancel usually asks a question, Yes or No will chose a different action and then proceed to do yet another action (like quitting a form), Cancel will abandon all actions.
For example: quitting Word, do you wish to save? "Yes, No, Cancel". Yes and No will continue to quit with or without saving, cancel will not save or quit.
Whatever you do, make sure Cancel does what the user expects most - I forever spam cancel if bombarded with message boxes when I have got to focus on something else. If I cancel something I don't want to lose a lot of work because I didn't have time to stop and handle it properly.
Users abuse cancel :-)

Sure there could be. For example, if there is a save dialog and you enter a filename that already exists, the dialog could ask you if you want to overwrite the file.
Yes would mean overwrite the file. No might mean append a "(1)" at the end of the file name, or prompt for a different file name. Cancel might mean don't save after-all.
You should note that Yes, No, and Cancel are all different enums and do not have the same value, so you can treat them differently.
REMEMBER TO HANDLE CANCEL ANYWAY because if the user clicks the x button in the top right corner of your dialog screen, the result of ShowDialog() is DialogResult.Cancel!

Here's an example of when YesNoCancel would be appropriate:
"Would you like to save your changes before quitting?"
Yes - Save and quit
No - Don't save and quit
Cancel - I pressed the button on accident, don't quit.

Im sure its easy enough to come up with a scenario where there would be a symantic difference between "No" as a response and "Cancel". Traditionally "Cancel" should return the program to its state before starting the current series of operations. "No" certainly doesnt have this same rule.
Example:
"Do you wish to delete file 4 of 10?"
Yes: Delete the file
No: Dont delete the file, move on to file 5 of 10
Cancel: Exit this operation and return to having not deleted any files.

I guess "Cancel" is used to abort the whole operation. If you are dealing with a huge procedure, for example, moving a set of files from one directory to another, you may want to ask something to the user about a specific file - for instance, to confirm if the user really wants to move a protected file. If the user presses "No", you ignore that item and continue the action. If the user presses "Cancel", you abort the whole action (and, maybe, rollback the previous action).
Of course, for a small procedure or a simple situation, "Cancel" and "No" have no difference.

Here's an example:
Say you are exiting an application with an unsaved file, like a word processor.
There is a confirmation when exiting that says: "Your file has changes that haven't been saved. Would you like to save them?"
In this case:
Yes = save the file and exit
No = exit and lose the changes
Cancel = abort the exit and go back to the application

C#: Is there a winforms way to make C# MessageBox Buttons (YesNo) larger?

It would be nice to have larger MessageBox Buttons since the target for this application is a tablet.
DialogResult dialogResult = MessageBox.Show(
message, caption,
MessageBoxButtons.YesNo,
MessageBoxIcon.Question,
MessageBoxDefaultButton.Button2);
switch (dialogResult)
{
case DialogResult.Yes:
// ...

It is a system setting. Tablet PCs are normally already configured to make it easy to tap buttons like this so that it works well in any program, not just yours. To configure your tablet, in Win7, use Control Panel + Display, Personalization, Window Color. Click Advanced appearance settings, select "Message Box" in the Item combo. Increase the font size. Don't be fooled by the poor preview, the button will actually grow. There are additional settings in this dialog you might want to tweak to make it easier to manipulate the UI.

A messagebox is just a simple modal form. You can make one yourself and use ShowDialog()

I'm not sure if it's possible or not, but you could use a simple form instead of a dialog box then you can get the design exactly as you wish.

Winforms way? Do you mean, an "automagically via a property change" way? If so, none that I know of.
You can spin up your own custom dialog/form that is bigger and use it instead. While this is not as automagic as the one line MessageBox.Show(), it is not very difficult.

That's not possible with MessageBox which wraps the native system dialog.
You'll need to produce your own dialog or even better see if there is a way to configure the system to give your app (and all others) bigger buttons.
The downside of rolling your own is that you lose all the functionality that the native one provides.

Yeah, going along with what MattP said, you'll need to create a custom form and then use the ShowDialog() method to display the second form as a modal dialog.
private void button2_Click(object sender, System.EventArgs e) {
using (Form2 xForm = new Form2()) {
if (xForm.ShowDialog(this) == DialogResult.OK) {
// Take some action
}
}
}

You can make a 2nd form, then you can make the buttons as big as you want

c# - create invisible user control

I need to create a user control in C#.Net, which can be added to the application without being visible - just like the FolderBrowserDialog. It's a new window which I'll be using often so I think this is the right way. The window will be opened by envoking the showDialog-Method as known from the other dialog.
Any Idea?
Thanks and regards,
Daniel

Since all these "invisible" controls derive from Component class, you should start by reading the MSDN article on it: http://msdn.microsoft.com/en-us/library/system.componentmodel.component.aspx.

simply set Visible to false or isn't this what you're asking for ?

A UserControl is by definition not a Form; I think what you really want is a Component. That said, couldn't you really just create a new Form class that has the functionality you want? Whenever you want to display it, create a new instance and call ShowDialog. Or, if you want to preserve state, add an instance as a class member to your parent form, call its Show method whenever you want to display it, and add an event handler to its FormClosing event to check:
if (e.CloseReason == CloseReason.UserClosing)
and, if so,
e.Cancel = true;
Hide();
(This last part is to prevent errors if the user closes the form and then tries to display again after it's been disposed.)

I think more information may be needed, but if your crating a custom user control, the control should have a .Visible property. The follow is an example of how a button can be located on the form but hidden from a user.
button.Visible = true; // shows the button
button.Show(); // Shows the button
button.Visible = false; // hides the button
button.Hide(); // Hides the button
While the button may still be on the form/control, it will not be interactible by the user. You can still perform programmatic control on the button, but essentially it is not a user control while it is 'hidden'. If you want there to be a sort of hidden button that the user can click you will need to do other things to obtain this but It doesn't should like that is what you want.

This show/hide thought process sounds a lot like pains and confusion leftover from classic VB. The old form methods of show and hide, etc., were confusing and often left me as a developer in a position to not know whether an object existed or if was merely invisible. And checking was only trivial if you used On Error Goto to prevent a null reference. So right off I would advise not to think in terms of visibility unless you are doing something with a web page and need to maintain space and state.
First, create a Windows form and add it to your project, assuming that is the type of project that you are describing. Decorate the form with the proper controls, and where applicable, create properties to allow public access to the control values. Also set the DialogResult property of the buttons that either "OK" or "Cancel" the form. Give it an appropriate border style of either Fixed3D or FixedDialog. Maybe also set the property for where you want the form to appear on startup -- center parent, center screen, Windows default, etc. The event handlers for both "OK" and "Cancel" should invoke this.Close(); to close the window.
From the calling point in the code, here's some hypothetical code to get you going in the right direction. Write something like this in the place where you want to invoke your Dialog.
int intResult = 0;
string strResult = null;
MyDialogForm frm = new MyDialogForm();
frm.Title = "Select an Item";
frm.SomeProperty = 0;
frm.SomeOtherProperty = true;
if (frm.ShowDialog() == DialogResult.OK)
{
intResult = frm.Result;
strResult = frm.StringResult;
}
else if (frm.ShowDialog() == DialogResult.Cancel)
{
// User clicked the cancel button. Nothing to do except maybe display a message.
MessageBox.Show("Canceled Task");
}
...
// Somewhere further on down, but within scope, simply repeat
// what you just did, but without having to reinstantiate the
// form Window. But if you make it that far within the same
// scope, this method might be too busy and may need to be
// factored down.
So in short:
Scrap show/hide -- its not a good
practice.
Save the form data without
using an invisible form to save it;
that's the class's job.
If the UI requires a lot of flipping back and
forth between windows, check your
design for other alternatives for
solving the original problem. Maybe a design pattern such as MVC is for you, depending upon the size and complexity of your application.
Sound good?

You can put that control in a Panel. Set the panel height = 0 visible = false when you dont want to show the control.
And do the vice versa when you want to show it.

Derive from Control, not UserControl, and in the constructor set Visible = false.
Also create an event handler in the constructor.
VisibleChanged += new EventHandler(SetVisibleFalse);
Create a method named SetVisibleFalse.
private void SetVisibleFalse(object sender, EventArgs e)
{
if (Visible) Visible = false;
}

.net C# windows Form Application : open popup window

I am using Windows Form application. I want to open a small textbox on a window to enter user's name or Email in Starting for the program.
How can I achieve this?

Write one, 'tis almost trivial (creating the form and adding label, textbox and buttons) and using the VB one is perputating something that was only put in to appease the baying mob.
Key method is ShowDialog() which is a method on a Form.
On the form make sure you set the flags for the Ok and Cancel buttons correctly and provide a property (ideally) to allow you to read (and write if necessary) the text box
You can then do something along the lines of the following:
using(MyInputForm mif = new MyInputForm)
{
if (mif.ShowDialog() == DialogResult.OK)
{
dataFromDialog = mif.InputData;
}
else
{
// logic to deal with cancel
}
}
You can do something similar in WPF, don't have an example to hand though.

Maybe the answer to this question will help:
What is the C# version of VB.net’s InputDialog?