| Description |
The Unit keyword is fundamental to Delphi, defining the start of a module.
Each Delphi module is stored in a Name.pas file, where Name must match the Unit Name.
Each unit comprises a set of interface definitions. Do not confuse these with class interfaces - the unit interface is the external interface to the module. It defines to any user of the unit what it contains. These interface definitions define private, protected, public and Published data, types and routine declarations.
Any routines defined in the interface must be implemented in the Implementation section. All function and procedure definitions must have exactly redefined arguments - see procedure and function information.
Optionally, you may have Initialization and Finalization sections. These contain statements executed when the unit is loaded and when it terminates, respectively.
If you only define an Initialization section, you may replace this keyword with Begin.
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| Related commands |
| Function |
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Defines a subroutine that returns a value |
| Implementation |
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Starts the implementation (code) section of a Unit |
| Interface |
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Used for Unit external definitions, and as a Class skeleton |
| Private |
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Starts the section of private data and methods in a class |
| Procedure |
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Defines a subroutine that does not return a value |
| Property |
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Defines controlled access to class fields |
| Protected |
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Starts a section of class private data accesible to sub-classes |
| Public |
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Starts an externally accessible section of a class |
| Published |
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Starts a published externally accessible section of a class |
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| Example code : A simple example |
// Full Unit code.
// -----------------------------------------------------------
// You must store this code in a unit called Unit1 with a form
// called Form1 that has an OnCreate event called FormCreate.
Unit Unit1;
// External interface to this unit module
interface
uses
Forms, Dialogs;
type
// Define the form class used by this unit
TForm1 = class(TForm)
// Define a procedure that must be implemented in the
// implementation section below
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
// Define a form - can be referenced in the Implementation section
Form1: TForm1;
// Implements the interface declarations above
implementation
{$R *.dfm}
procedure TForm1.FormCreate(Sender: TObject);
begin
// Set and show the form title
Form1.Caption := 'Test program';
WriteLn('Running = '+Form1.Caption);
end;
initialization
// Tell the user we are starting this unit
WriteLn('Initialising');
end.
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| Show full unit code |
Initialising
Running Test program
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