在VB.NET中创建可以在C＃中使用的索引器

Question

Can I create a class in VB.NET which can be used from C# like that:

myObject.Objects[index].Prop = 1234;

Sure I could create a property which returns an array. But the requirement is that the index is 1-based, not 0-based, so this method has to map the indices somehow:

I was trying to make it like that, but C# told me I cannot call this directly:

   Public ReadOnly Property Objects(ByVal index As Integer) As ObjectData
        Get
            If (index = 0) Then
                Throw New ArgumentOutOfRangeException()
            End If
            Return parrObjectData(index)
        End Get
    End Property

EDIT Sorry if I was a bit unclear:

C# only allows my to call this method like

myObject.get_Objects(index).Prop = 1234

but not

myObject.Objects[index].Prop = 1234;

this is what I want to achieve.

Answer 1

The syntax is:

Default Public ReadOnly Property Item(ByVal index as Integer) As ObjectData
  Get
    If (index = 0) Then
      Throw New ArgumentOutOfRangeException()
    End If
    Return parrObjectData(index)
  End Get
End Property

The Default keyword is the magic that creates the indexer. Unfortunately C# does not support named indexers. You are going to have to create a custom collection wrapper and return that instead.

Public ReadOnly Property Objects As ICollection(Of ObjectData)
  Get
    Return New CollectionWrapper(parrObjectData)
  End Get
End Property

Where the CollectionWrapper might would look like this:

Private Class CollectionWrapper
  Implements ICollection(Of ObjectData)

  Private m_Collection As ICollection(Of ObjectData)

  Public Sub New(ByVal collection As ICollection(Of ObjectData))
    m_Collection = collection
  End Sub

  Default Public ReadOnly Property Item(ByVal index as Integer) As ObjectData
    Get
      If (index = 0) Then
        Throw New ArgumentOutOfRangeException()
      End If
      Return m_Collection(index)
    End Get
  End Property

End Class

Answer 2

You can fake named indexers in C# using a struct with a default indexer:

public class ObjectData
{
}

public class MyClass
{
    private List<ObjectData> _objects=new List<ObjectData>();
    public ObjectsIndexer Objects{get{return new ObjectsIndexer(this);}}

    public struct ObjectsIndexer
    {
        private MyClass _instance;

        internal ObjectsIndexer(MyClass instance)
        {
            _instance=instance;
        }

        public ObjectData this[int index]
        {
            get
            {
                return _instance._objects[index-1];
            }
        }
    }
}

void Main()
{
        MyClass cls=new MyClass();
        ObjectData data=cls.Objects[1];
}

If that's a good idea is a different question.

Answer 3

C＃不支持命名索引属性的声明（尽管您可以创建索引器），但是您可以通过显式调用setter或getter来访问在其他语言（如VB）中声明的索引属性（ get_MyProperty / set_MyProperty ）

Answer 4

Why not make use of the 0 based indexing but give the illusion to the coder that it is 1 based?

ie

Return parrObjectData(index-1)