Understand the Delphi Class (III)

Unit Unit1;

interface
uses
　Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
　Dialogs, StdCtrls;
type
　TForm1 = class(TForm)
　　Button1: TButton;
　　procedure Button1Click(Sender: TObject);
　end;There are only two fields in the TMyClass1 class (the variable comes to the class to be called the field) 　 TMyClass1 = class
　　FName: string;　{字段命名一般用 F 开头, 应该是取 field 的首字母}
　　FAge:　Integer; {另外: 类的字段必须在方法和属性前面}
　end;
　{这个类中的两个字段, 可以随便读写; 在实际运用中, 这种情况是不存在的.} //tmyclass2 class contains two properties (property), two methods, two and TMyClass1 the same fields　TMyClass2 = class
　strict private
　　FName: string;
　　FAge:　Integer;
　　procedure SetAge(const Value: Integer);
　　procedure SetName(const Value: string);
　published
　　property Name: string　read FName write SetName;
　　property Age:　Integer read FAge　write SetAge;
　end;
　{

But here's the fields: FName, Fage and methods: Setage, SetName is not accessible,

Because they are encapsulated in the strict private area, they can only be used inside the class after encapsulation.

There are three elements in the attribute:

1. Specify the data type: For example, the age attribute is an Integer type;

2, how to read: For example, read the age attribute, actually read the Fage field;

3, how to write: such as Hill age attribute, is actually through the Setage method.

Property is just a bridge.

What is the difference between a property access field and a direct access field?

By attributes can give access to a certain limit,

For example: A person's age can not be more than 200 years old, and will not be negative; A person's name should not be a null value.

This limitation is increased by looking at the implementation of the two methods of the TMyClass2 class in the implementation area.

　 }
var
　Form1: TForm1;
implementation
{$R *.dfm}
{ TMyClass2 }
procedure TMyClass2.SetAge(const Value: Integer);
begin
　if (Value>=0) and (Value<200) then
　　FAge := Value;
end;
procedure TMyClass2.SetName(const Value: string);
begin
　if Value<>'' then
　　FName := Value;
end;

Test:

procedure TForm1.Button1Click(Sender: TObject);
var
　class1: TMyClass1;
　class2: TMyClass2;
begin
　class1 := TMyClass1.Create;
　class2 := TMyClass2.Create;
　class1.FAge := 1000; {TMyClass1 中的 FAge 字段可以接受一个离奇的年龄}
　class2.Age　:= 99;　 {通过 TMyClass2 中的 Age 属性, 只能赋一个合理的值}
//class2.FAge := 99; {TMyClass2 中的 FAge 字段被封装了, 在这里无法使用}
　class1.Free;
　class2.Free;
end;

End.