When a form is being created and its Visible property
is true, the following events occur in the order listed:

1. OnCreate
2. OnShow
3. OnActivate
4. OnPaint

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The TCloseEvent type points to a method that handles the closing of a form. The value of the Action parameter determines if the form actually closes. These are the possible values of Action:

caNone The form is not allowed to close, so nothing happens.
caHide The form is not closed, but just hidden. Your application can still access a hidden form.
caFree The form is closed and all allocated memory for the form is freed.
caMinimize The form is minimized, rather than closed. This is the default action for MDI child forms.

To close the form and free it in an OnClose event, set Action to caFree.

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OnCloseQuery Occurs when close is attempted.

An OnCloseQuery event handler returns a Boolean CanClose value that
determines whether a form is allowed to close. Its default value is true.