CreateInstanceAttribute Class

Specifies that a Domain Component‘s target method will create Domain Component instances.

Namespace: DevExpress.ExpressApp.DC

Assembly: DevExpress.ExpressApp.v23.2.dll

NuGet Package: DevExpress.ExpressApp

Declaration

C#

[AttributeUsage(AttributeTargets.Method)]
public class CreateInstanceAttribute :
    Attribute

VB.NET

<AttributeUsage(AttributeTargets.Method)>
Public Class CreateInstanceAttribute
    Inherits Attribute

Remarks

When implementing a Domain Component, you can define a method that will create Domain Component instances. For this purpose, the method must be parameterless, have the required return type, and be decorated with the CreateInstanceAttribute.

C#

[DomainComponent]
public interface IAddress {
    string PrimaryAddress { get; set; }
    string SecondaryAddress { get; set; }
}
[DomainComponent]
public interface IPerson {
    IAddress Address { get; set; }
    [CreateInstance]
    IAddress CreateAddress();
}
[DomainLogic(typeof(IPerson))]
public class PersonLogic {
    public static void AfterConstruction(IPerson person) {
        if(person.Address == null) {
            person.Address = person.CreateAddress();
        }
    }
}

VB.NET

<DomainComponent> _
Public Interface IAddress
    Property PrimaryAddress() As String
    Property SecondaryAddress() As String
End Interface
<DomainComponent> _
Public Interface IPerson
    Property Address() As IAddress
    <CreateInstance> _
    Function CreateAddress() As IAddress
End Interface
<DomainLogic(GetType(IPerson))> _
Public Class PersonLogic
    Public Shared Sub AfterConstruction(ByVal person As IPerson)
        If person.Address Is Nothing Then
            person.Address = person.CreateAddress()
        End If
    End Sub
End Class

You can override the type of Domain Components created by a method, by using the CreateInstanceAttribute constructor taking a Type parameter.

C#

[DomainComponent]
public interface IExtendedAddress : IAddress { }
[DomainComponent]
public interface IPerson {
    IAddress Address { get; set; }
    [CreateInstance(typeof(IExtendedAddress))]
    IAddress CreateAddress();
}

VB.NET

<DomainComponent> _
Public Interface IExtendedAddress
    Inherits IAddress
End Interface
<DomainComponent> _
Public Interface IPerson
    Property Address() As IAddress
    <CreateInstance(GetType(IExtendedAddress))> _
    Function CreateAddress() As IAddress
End Interface

If an application has several registered entities implementing the interface, specified as the CreateInstanceAttribute.InstanceType, the CreateInstanceAttribute will not be able to determine what type of Domain Components must be created by the method, and an exception will be thrown. In this instance, you need to define the logic for the method, and explicitly specify what type must be instantiated.

C#

[DomainComponent]
public interface ICustomAddress : IAddress { }
[DomainLogic(typeof(IPerson))]
public class AdditionalPersonLogic {
    public static IAddress CreateAddress(IPerson source, IObjectSpace os) {
        return os.CreateObject<ICustomAddress>();
    }
}

VB.NET

<DomainComponent> _
Public Interface ICustomAddress
    Inherits IAddress
End Interface
<DomainLogic(GetType(IPerson))> _
Public Class AdditionalPersonLogic
    Public Shared Function CreateAddress(ByVal source As IPerson, ByVal os As IObjectSpace) _
    As IAddress
        Return os.CreateObject(Of ICustomAddress)()
    End Function
End Class

Inheritance

Object

Attribute

CreateInstanceAttribute