This

This : Object

Parâmetro	Tipo		Descrição
Resultado	Object	←	Current element or object

Descrição

O comando This retorna uma referência ao objeto processado atualmente.

Na maioria dos casos, o valor de Isso é determinado pela forma como uma função é chamada. Não pode ser definido por atribuição durante a execução e pode ser diferente de cada vez que a função é chamada.

This command can be used in different contexts, described below. Within these contexts, you will access object/collection element properties or entity attributes through This.<propertyPath>. For example, This.name or This.employer.lastName are valid pathes to object, element or entity properties.

Em qualquer outro contexto, o comando retorna Null.

Função de classe

Quando uma função construtor de classe é usada (com a new()), sua This estará ligada ao novo objeto que está sendo construído.

//Class: ob

Class Constructor  

 // Create properties on This as
 // desired by assigning to them

 This.a:=42

// num método 4D  
$o:=cs.ob.new()
$val:=$o.a //42

When calling the superclass constructor in a constructor using the Super keyword, keep in mind that This must not be called before the superclass constructor, otherwise an error is generated. Veja este exemplo.

Em qualquer caso, This refere-se ao objeto em que o método foi chamado, como se o método estivesse no objeto.

//Class: ob

Function f() : Integer
 return This.a+This.b

Depois pode escrever num método projecto:

$o:=cs.ob.new()
$o.a:=5
$o.b:=3
$val:=$o.f() //8

Neste exemplo, o objeto atribuído à variável $o não tem sua própria propriedade f, herda-o de sua classe. Uma vez que f é chamado como um método de $o, o seu This refere-se a $o.

Objecto fórmula

In the context of the execution of a formula object created by the Formula or Formula from string commands, This returns a reference to the object currently processed by the formula.

For example, you want to use a project method as a formula encapsulated in an object:

 var $person : Object := New object
 $person.firstName:="John"
 $person.lastName:="Smith"
 $person.greeting:=Formula(Greeting)
 $g:=$person.greeting("hello") // returns "hello John Smith"
 $g:=$person.greeting("hi") // returns "hi John Smith"

With the Greeting project method:

 #DECLARE($greeting : Text) : Text
 return $greeting+" "+This.firstName+" "+This.lastName

List box

In the context of a list box associated to a collection or an entity selection, during the On Display Detail or the On Data Change events, This returns a reference to the collection element or entity accessed by the list box to display the current row.

nota

If you use a collection of scalar values in a list box, 4D creates an object for each element with a single value property. Thus, the element value is returned by the This.value non-assignable expression.

Exemplo 1

A collection of objects, each with this structure:

{  
"ID": 1234
"name": "Xavier",  
"revenues": 47300,  
"employees": [  
             "Allan",  
             "Bob", 
             "Charlie"  
            ] 
},{  
"ID": 2563
"name": "Carla",  
"revenues": 55000,  
"isFemale": true
"employees": [  
             "Igor",  
             "Jane"  
            ] 
},...
 

In the list box, each column refers to one of the properties of the object, either directly (This.name), indirectly (This.employees.length), or through an expression (getPicture) in which can be used directly. O list box parece com:

The GetPicture project method is automatically executed during the On display detail event:

  //GetPicture Method
 #DECLARE -> $genderPict : Picture
 If(This.isFemale)
    $genderPict:=Form.genericFemaleImage
 Else
    $genderPict:=Form.genericMaleImage
 End if

Once the form is executed, you can see the result:

Exemplo 2

You want to display entities from the following structure in a list box:

You build a list box of the "Collection or entity selection" type with the following definition:

Note que:

• This.ID, This.Title and This.Date directly refers to the corresponding attributes in the ds.Event dataclass.
• This.meetings is a related attribute (based upon the One To Many relation name) that returns an entity selection of the ds.Meeting dataclass.
• Form.eventList is the entity selection that is attached to the list box. The initialization code can be put in the on load form event:

 Case of  
    :(Form event code=On Load)  
       Form.eventList:=ds.Event.all() //returns an entity selection with all entities  
 End case  

Once the form is executed, the list box is automatically filled with the entity selection:

Veja também

Self
Super

Propriedades

Command number	1470
Thread safe	✓