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Property Statement 

Declares the name of a property, and the property procedures used to store and retrieve the value of the property.


[ <attributelist> ] [ Default ] [ accessmodifier ] 
[ propertymodifiers ] [ Shared ] [ Shadows ] [ ReadOnly | WriteOnly ] 
Property name ( [ parameterlist ] ) [ As returntype ] [ Implements implementslist ]
    [ <attributelist> ] [ accessmodifier ] Get
        [ statements ]
    End Get
    [ <attributelist> ] [ accessmodifier ] Set ( ByVal value As returntype [, parameterlist ] )
        [ statements ]
    End Set
End Property

attributelist

Optional. List of attributes that apply to this property or Get or Set procedure. See Attribute List.

Default

Optional. Specifies that this property is the default property for the class or structure on which it is defined. Default properties must accept parameters and can be set and retrieved without specifying the property name. If you declare the property as Default, you cannot use Private on the property or on either of its property procedures.

accessmodifier

Optional on the Property statement and on at most one of the Get and Set statements. Can be one of the following:

See Access Levels in Visual Basic.

propertymodifiers

Optional. Can be one of the following:

Shared

Optional. See Shared (Visual Basic).

Shadows

Optional. See Shadows.

ReadOnly

Optional. See ReadOnly (Visual Basic).

WriteOnly

Optional. See WriteOnly.

name

Required. Name of the property. See Declared Element Names.

parameterlist

Optional. List of local variable names representing the parameters of this property, and possible additional parameters of the Set procedure. See Parameter List.

returntype

Required if Option Strict is On. Data type of the value returned by this property.

Implements

Optional. Indicates that this property implements one or more properties, each one defined in an interface implemented by this property's containing class or structure. See Implements Statement.

implementslist

Required if Implements is supplied. List of properties being implemented.

implementedproperty [ , implementedproperty ... ]

Each implementedproperty has the following syntax and parts:

interface.definedname

Part Description

interface

Required. Name of an interface implemented by this property's containing class or structure.

definedname

Required. Name by which the property is defined in interface.

Get

Required unless the property is marked WriteOnly. Starts a Get property procedure used to return the value of the property.

statements

Optional. Block of statements to run within the Get or Set procedure.

End Get

Terminates the Get property procedure.

Set

Required unless the property is marked ReadOnly. Starts a Set property procedure used to store the value of the property.

End Set

Terminates the Set property procedure.

End Property

Terminates the definition of this property.

The Property statement introduces the declaration of a property. A property can have a Get procedure (read only), a Set procedure (write only), or both (read-write).

You can use Property only at module level. This means the declaration context for a property must be a class, structure, module, or interface, and cannot be a source file, namespace, procedure, or block. For more information, see Declaration Contexts and Default Access Levels.

Properties default to public access. You can adjust a property's access level with an access modifier on the Property statement, and you can optionally adjust one of its property procedures to a more restrictive access level.

Visual Basic passes a parameter to the Set procedure during property assignments. If you do not supply a parameter for Set, the integrated development environment (IDE) uses an implicit parameter named value. This parameter holds the value to be assigned to the property. You typically store this value in a private local variable and return it whenever the Get procedure is called.

Rules

  • Mixed Access Levels. If you are defining a read-write property, you can optionally specify a different access level for either the Get or the Set procedure, but not both. If you do this, the procedure access level must be more restrictive than the property's access level. For example, if the property is declared Friend, you can declare the Set procedure Private, but not Public.

    If you are defining a ReadOnly or WriteOnly property, the single property procedure (Get or Set, respectively) represents the entire property. You cannot declare a different access level for such a procedure, because that would set two access levels for the property.

  • Return Type. The Property statement can declare the data type of the value it returns. You can specify any data type or the name of an enumeration, structure, class, or interface.

    If you do not specify returntype, the property returns Object.

  • Implementation. If this property uses the Implements keyword, the containing class or structure must have an Implements statement immediately following its Class or Structure statement. The Implements statement must include each interface specified in implementslist. However, the name by which an interface defines the Property (in definedname) does not have to be the same as the name of this property (in name).

Behavior

  • Returning from a Property Procedure. When the Get or Set procedure returns to the calling code, execution continues with the statement following the statement that invoked it.

    The Exit Property and Return statements cause an immediate exit from a property procedure. Any number of Exit Property and Return statements can appear anywhere in the procedure, and you can mix Exit Property and Return statements.

  • Return Value. To return a value from a Get procedure, you can either assign the value to the property name or include it in a Return statement. The following example assigns the return value to the property name quoteForTheDay and then uses the Exit Property statement to return.

    Private quoteValue As String = "No quote assigned yet."
    
    
    ReadOnly Property quoteForTheDay() As String
        Get
            quoteForTheDay = quoteValue
            Exit Property
        End Get
    End Property
    
    

    If you use Exit Property without assigning a value to name, the Get procedure returns the default value for the property's data type.

    The Return statement simultaneously assigns the Get procedure return value and exits the procedure. The following example shows this.

    Private quoteValue As String = "No quote assigned yet."
    
    
    ReadOnly Property quoteForTheDay() As String
        Get
            Return quoteValue
        End Get
    End Property
    
    

The following example declares a property in a class.

Class Class1
    ' Define a local variable to store the property value.
    Private propertyValue As String
    ' Define the property.
    Public Property prop1() As String
        Get
            ' The Get property procedure is called when the value
            ' of a property is retrieved.
            Return propertyValue
        End Get
        Set(ByVal value As String)
            ' The Set property procedure is called when the value 
            ' of a property is modified.  The value to be assigned
            ' is passed in the argument to Set.
            propertyValue = value
        End Set
    End Property
End Class

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