Mega Code Archive
Anatomy Of A Project 101
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Title: Anatomy Of A Project 101
Question: In the "Anatomy Of A Project" series, I'm going to be going through all of the base pieces that make up your application. From the base unit code to enumerations to class composition and visibility, this will be a non-functional series, and will be more of a reference than a tutorial.
Class 101 will focus on the code generated when you create a new form.
Answer:
unit Training;
// The unit name consists only of the filename of the current unit.
interface
// The interface section contains all class, property, variable and
// method declarations.
uses
// The interface uses clause defines unit methods that will be
// referenced by the declarations AND the implementations.
// There is a danger in this uses section of circular
// references. A circular reference is when Unit1
// references Unit2 in the interface section, and Unit2
// references Unit1 in the interface section.
Windows, Messages, SysUtils, Classes, Graphics, Controls,
Forms, Dialogs;
type
// The type clause contains all class declaractions in the current
// unit.
TfrmTraining = class( TForm )
// The form in question is automatically created as a class.
// The type is the form component's Name property, with
// a 'T' preceding it. In general, all forms are decended
// from TForm, though it is possible to inherit from
// any Object Pascal class.
private
// Private declarations will be visible only to the
// class in which they reside (the form, in this case),
// any decendants of the class, or to anything physically
// implemented within this unit.
public
// Public declarations will be visible to any external units
// or classes.
end;
var
// The var clause in the interface section defines unit-level
// variables. By default, the form is the only variable
// declared, with the component name declared as the
// previously defined class. It is considered bad form in
// general to make your own variable declarations here, as
// they would be globals. This is not to say that globals
// are always a bad idea, and there are cases where
// globals are desirable. In a future article, I will
// discuss this. But for now, I will simply point out
// that if you are using global variables or functions,
// that you have a reason that you are not encapsulating
// them into a class.
frmTraining: TfrmTraining;
implementation
// The implementation section is where the actual implementation of
// the previously defined classes will be written. If you have
// written a class method in the interface section, you can press
// CTRL-SHIFT-C to have the IDE automatically write the shell for
// the method's implementation. In addition, you can
// quickly navigate between a method's interface and
// implementation by pressing CTRL-SHIFT-DOWN ARROW or
// CTRL_SHIFT_UP ARROW.
{$R *.DFM}
// This is a compiler directive. We're not going to go into them
// now, though I'll provide the short explanation that this
// includes as resource files ($R) the file in the directory with
// the unit name and a DFM extension (*.DFM). The DFM file stores
// your form's design-time information and internal component
// properties.
end.
// The "end." statement marks the end of the unit. No code beyond
// this point will be valid.
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