NewItemInstanceInitializerAttribute.CreateInstance(ITypeDescriptorContext, IEnumerable) Method

Creates a dictionary item with a key/value pair.

Namespace: DevExpress.Mvvm.DataAnnotations

Assembly: DevExpress.Mvvm.v24.2.dll

Declaration

C#

public virtual KeyValuePair<object, object>? CreateInstance(
    ITypeDescriptorContext context,
    IEnumerable dictionary
)

VB.NET

Public Overridable Function CreateInstance(
    context As ITypeDescriptorContext,
    dictionary As IEnumerable
) As KeyValuePair(Of Object, Object)?

Parameters

Name	Type	Description
context	ITypeDescriptorContext	Context information about a new dictionary item to be created.
dictionary	IEnumerable	A new dictionary item to be created.

Returns

Type	Description
Nullable<KeyValuePair<Object, Object>>	A KeyValuePair object that contains the key/value pair.

Remarks

This method allows you to create a new dictionary item with a key/value pair. The default implementation returns null.

In the following code sample, the CreateInstance method overrides the base implementation to create a new dictionary item where the key is a unique integer string and the value is an instance of ItemInitializer.

C#

public class DictionaryKey1 : NewItemInstanceInitializerAttribute {
    public DictionaryKey1(Type type) : base(type) { }
    public override KeyValuePair<object, object>? CreateInstance(ITypeDescriptorContext context, IEnumerable dictionary) {
        var testObject = ((DescriptorContext)context).Value as IDictionary<string, object>;
        int key = testObject.Keys.Count;
        while(testObject.Keys.Contains(key.ToString()))
            key++;
        return new KeyValuePair<object, object>(key.ToString(), new ConcreteClass());
    }
}

VB.NET

Public Class DictionaryKey1
Inherits NewItemInstanceInitializerAttribute
Public Sub New(ByVal type As Type)
    MyBase.New(type)
End Sub
Public Overrides Function CreateInstance(ByVal context As ITypeDescriptorContext, ByVal dictionary As IEnumerable) As KeyValuePair(Of Object, Object)?
    Dim testObject = TryCast(context, DescriptorContext)?.Value as IDictionary(Of String, Object)
    Dim key As Integer = testObject.Keys.Count    
    While testObject.Keys.Contains(key.ToString())
        key += 1
    End While    
    Return New KeyValuePair(Of Object, Object)(key.ToString(), New ItemInitializer())
End Function
End Class