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How to stop windows form from closing but hide upon clicking the X?

I'm trying to have a click event that will open another form. I don't want the user to be able to close this window because I get the following exception when the click event is executed again.
System.ObjectDisposedException: 'Cannot access a disposed object.
Object name: 'Form2'.'
I'm not sure if I'm implementing this correctly or there's a better way of doing this.
Form1
public Form2 f = new Form2();
private void Btnsearch_Click(object sender, EventArgs e)
{
f.Show();
}
Form2
private bool allowClose = false;
private void Btnclose_Click(object sender, EventArgs e)
{
allowClose = true;
this.Hide();
}
private void Form2_FormClosing(object sender, FormClosingEventArgs e)
{
if (!allowClose)
e.Cancel = true;
}

Subscribe to Form.OnClosing and set the Cancel property on the event args that are passed to the handler. This will tell the runtime to cancel the close event.
Since the event is getting canceled, you'll have to hide the form yourself (using Hide(), of course).
private void Form1_Closing(Object sender, CancelEventArgs e)
{
this.Hide();
e.Cancel = true;
}

The instance of form2 should be created within the event
private void Btnsearch_Click(object sender, EventArgs e)
{
Form2 f = new Form2();
f.Show();
}

There are a couple of ways to approach this.
It's generally more efficient, in the FormClosing event, to hide the form and cancel the event, but this can require extra logic.
Unless you have some expensive code that needs to run when the form is created, this probably doesn't matter, and it'll be easier to simply allow the form to close normally.
Either way, all you particularly need to do, is throw some safeguards into the btnSearch handler, so that it can appropriately respond to the state of form f;
public Form2 f;
public void BtnSearch_Click(object sender, EventArgs e)
{
if (f == null || f.IsDisposed || f.Disposing) f = new Form2(...);
f.Show();
}

Close WinForm On Button Click

I have this syntax on my buton press event, but when I press it - the form does not close.
What is the proper way to close the form on the button press event?
private void btnClose_Click(object sender, EventArgs e)
{
IxalocToes nip = new IxalocToes();
nip.Close();
}

This method btnClose_Click runs inside your forms class
Forms have a method call Close, calling Close() or this.Close() inside the form will close it
private void btnClose_Click(object sender, EventArgs e)
{
IxalocToes nip = new IxalocToes();
nip.Close();
Close();
}

As suggested by many and it is right, calling
this.Close() or
Close()
will close the form. As you want to know why nip.Close() is not working, it's because the button is in a FORM but when you call nip.Close() instead of this.Close(), it will close the new object created, not the one on which the button resides.

Stackoverflow Exception closing Form

I have a problem in WinForms. I created a MDIParent-Form and i call a ChildForm from the Load of the MDIParent. And I want that if the ChildForm closes, the MDIParent must close and the Application exits. Thats why i wrote an event for the childForm in the MDIParent, so that if the ChildForm closes the FormClosed-Event would be fired in the MDIParent, but it throws a stack overflow exception. I know that there is a infinite loop, but I dont know why...
private void MDIParent1_Load(object sender, EventArgs e)
{
Form1 childForm = new Form1();
childForm.MdiParent = this;
childForm.FormClosed += childForm_FormClosed;
childForm.Show();
}
void childForm_FormClosed(object sender, FormClosedEventArgs e)
{
this.Close();
//{Cannot evaluate expression because the current thread is in a stack overflow state.}
}
but if i use
Application.Exit();
instead of this.Close()... everything works fine ... i want to know why...can someone explain??
Update:
I have tried the same without a MDIParent and everything works...but why is there a problem if I use a MDIParent

This is a bit of a bug, the problem is that the child still is present in the MDIParent1.MdiChildren collection when the FormClosed event fires. In other words, the FormClosed event fires a little too soon. So when you close the parent, it will try to close the child again. Which triggers the child's FormClosed event again. Which closes the parent again. Etcetera. Event firing order is never not a problem. Well, let's call it a bug :)
The workaround is to use the Disposed event instead, it fires later:
private void MDIParent1_Load(object sender, EventArgs e)
{
Form1 childForm = new Form1();
childForm.MdiParent = this;
childForm.Disposed += childForm_Disposed;
childForm.Show();
}
void childForm_Disposed(object sender, EventArgs e)
{
this.Close(); // Fine now
}

How to show Notification Message on Shutdown of Application WPF

I made application in which when user will click on close button of MainWindow whole application will shutdown. I want to show a Notification after closing of application. How to show a toast message as application shuts'down?
Here Code is :
private void Close(object sender, EventArgs e)
{
base.OnClosed(e);
Application.Current.Shutdown();
}
Can any one answer my question?
Feel Free to ask if my question is not clear!

Try implementing a handler for the Window.Closing event:
private void MainWindow_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
MessageBox.Show("Hi, I'm closing!");
}
This will occur before the Window.Closed event.
UPDATE >>>
#Andy and Tameen, please take a look at the Window.Closing Event page at MSDN to see when this event really occurs.
Occurs directly after Close is called, and can be handled to cancel window closure.
UPDATE 2 >>>
Your question does not state that you want to cancel the Close event. However, that is exactly what the Closing event is for:
private void MainWindow_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
MessageBox.Show("Hi, I'm closing!");
e.Cancel = true;
}

Your application shutdowns by default when the mainwindow closes. Allow the button to signal the window close and handle the toast in the Closed event.
<Window ... Closed="Window_Closed" />
private void Button_Click(object sender, RoutedEventArgs e)
{
this.Close();
}
private void Window_Closed(object sender, EventArgs e)
{
MessageBox.Show("Cya");
}

Closing a form and doing something on return to another form

I have a mainForm and a saveForm.
I never close the mainForm, just let the saveForm appear over the top.
When i close the saveForm, I want a piece of code to run on returning to mainForm.
What is the best way to achieve this?

In addition to #benPearce's answer, if you are content to have saveForm appear modally, then you can just call:
So in the mainForm, I am assuming you have a Save button (let's call it btnSave) of some kind that brings up saveForm, right? Right. So double click on that Save button and Visual Studio will create an event handler for you. Type in the code below.
private void btnSave_Click(object sender, EventArgs e)
{
saveForm sf = new SaveForm();
if (sf.ShowDialog() == DialogResult.OK)
{
// do your thing
}
}
Of course, you have to make sure that the saveForm is setting the DialogResult. For instance, assuming you have an OK button in the saveForm that is supposed to close the saveForm... In the Click event for the OK button you would do this:
private void btnOK_Click(object sender, EventArgs e)
{
this.DialogResult = DialogResult.OK;
this.Close();
}

In mainForm, subscribe to the FormClosed event on the saveForm, put your code in the event handler for this event
void saveForm_FormClosed(object sender, FormClosedEventArgs e)
{
/// code here
}