Using the typical get set properties in C#... with parameters

Question

I'd like to do the same in C#. Is there anyway of using properties in C# with parameters in the same way I've done with the parameter 'Key' in this VB.NET example?

Private Shared m_Dictionary As IDictionary(Of String, Object) = New Dictionary(Of String, Object)

Public Shared Property DictionaryElement(ByVal Key As String) As Object
    Get
        If m_Dictionary.ContainsKey(Key) Then
            Return m_Dictionary(Key)
        Else
            Return [String].Empty
        End If
    End Get
    Set(ByVal value As Object)
        If m_Dictionary.ContainsKey(Key) Then
            m_Dictionary(Key) = value
        Else
            m_Dictionary.Add(Key, value)
        End If

    End Set
End Property

Thanks

Answer 1

Is there anyway of using properties in C# with parameters

No. You only can provide the default property in C# with an argument, to model indexed access (as in a dictionary):

public T this[string key] {
    get { return m_Dictionary[key]; }
    set { m_Dictionary[key] = value; }
}

Other properties can't have arguments. Use a function instead. By the way, it's recommented to do the same in VB so other .NET languages (C# …) can use your code.

By the way, your code is unnecessarily complicated. Four things:

• You don't need to escape the String identifier. Use the keyword directly.
• Why not use ""?
• Use TryGetValue, it's faster. You query the dictionary twice.
• Your setter doesn't have to test whether the value already exists.

---

Public Shared Property DictionaryElement(ByVal Key As String) As Object
    Get
        Dim ret As String
        If m_Dictionary.TryGetValue(Key, ret) Then Return ret
        Return "" ' Same as String.Empty! '
    End Get
    Set(ByVal value As Object)
        m_Dictionary(Key) = value
    End Set
End Property

Answer 2

The "proper" way to do it in C# is to create child class specifically to access the collection. It should either hold the collection itself or have internal linkages to the parent class.

Answer 3

A more general-purpose, safer, and reusable solution to your problem might be implementing a generic, "parameterized" property class, like this:

    // Generic, parameterized (indexed) "property" template
    public class Property<T>
    {
        // The internal property value
        private T PropVal = default(T);

        // The indexed property get/set accessor 
        //  (Property<T>[index] = newvalue; value = Property<T>[index];)
        public T this[object key]
        {
            get { return PropVal; }     // Get the value
            set { PropVal = value; }    // Set the value
        }
    }

You could then implement any number of properties within your public class so that clients could set/get the properties with an index, descriptor, security key, or whatever, like this:

    public class ParameterizedProperties
    {
        // Parameterized properties
        private Property<int> m_IntProp = new Property<int>();
        private Property<string> m_StringProp = new Property<string>();

        // Parameterized int property accessor for client access
        //  (ex: ParameterizedProperties.PublicIntProp[index])
        public Property<int> PublicIntProp
        {
            get { return m_IntProp; }
        }

        // Parameterized string property accessor
        //  (ex: ParameterizedProperties.PublicStringProp[index])
        public Property<string> PublicStringProp
        {
            get { return m_StringProp; }
        }
    }

Finally, client code would access your public class's "parameterized" properties like this:

        ParameterizedProperties parmProperties = new ParameterizedProperties();
        parmProperties.PublicIntProp[1] = 100;
        parmProperties.PublicStringProp[1] = "whatever";
        int ival = parmProperties.PublicIntProp[1];
        string strVal = parmProperties.PublicStringProp[1];

Sure, this seems weird, but it definitely does the trick. Besides, from a client-code perspective, it's not weird at all -- it's simple and intuitive and acts just like real properties. It doesn't break any C# rules, nor is it incompatible with other .NET managed languages. And from the class-implementer's perspective, creating a reusable, generic, "parameterized" property template class makes component coding a relative breeze, as shown here.

NOTE: You can always override the generic property class to provide custom processing, such as indexed lookup, security-controlled property access, or whatever-the-heck you want.

Cheers!

Mark Jones

Answer 4

Here is a sample for you (with changes along the lines of Grauenwolf's suggestions):

using System;
using System.Collections.Generic;

public class Test
{
    public FakeIndexedPropertyInCSharp DictionaryElement { get; set; }

    public Test()
    {
        DictionaryElement = new FakeIndexedPropertyInCSharp();
    }

    public class FakeIndexedPropertyInCSharp
    {
        private Dictionary<string, object> m_Dictionary = new Dictionary<string, object>();

        public object this[string index]
        {
            get 
            {
                object result;
                return m_Dictionary.TryGetValue(index, out result) ? result : null;
            }
            set 
            {
                m_Dictionary[index] = value; 
            }
        }
    }


}

class Program
{
    static void Main(string[] args)
    {
        Test t = new Test();
        t.DictionaryElement["hello"] = "world";
        Console.WriteLine(t.DictionaryElement["hello"]);
    }
}

Answer 5

Your code sample strikes me as a very strange design and an abuse of what properties are intended for. Why not just an instance method AddOrUpdateKey:

Public Sub AddOrUpdateKey(ByVal Key As String, ByVal Value as Object)
    If m_Dictionary.ContainsKey(Key) Then
        m_Dictionary(Key) = Value
    Else
        m_Dictionary.Add(Key, Value)
    End If
End Sub

Your property also returns String.Empty if the key does not exist, but claims to return an Object, nor a String.

Answer 6

Thanks Konrad, Alan, Grauenwolf,

In conclusion, I can't use C# properties exactly in the same way that in VB.NET... :_( Anyway, your answers has been very usefull to me, and I´ll probably take this ideas to my C# code.

In addition to the answers to the properties question, there are other good points. For example,

• Use TryGetValue, it's faster. You query the dictionary twice.
• Your setter doesn't have to test whether the value already exists.

Thanks Sören, too, using a method don't fits well in my initial aims, but thanks very much.