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

1
9
10/25/2008 2:56:48 PM

Accepted Answer

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
14
10/25/2008 3:12:08 PM

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


Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow
Icon