Reflection

Back in the old days, C++ templates were the highest level of code abstraction for me. I loved creating template classes. On the other hand, Reflection, when I first learned about it, it didn't raise such an emotional feeling in me. It seamed like a complicated way to do simple things. About a year ago I was lucky to work with John Volkar from Bayer Healthcare. His project used Reflection to transform between C# data members and DICOM data elements. Recently, while working on another project, this technique came in handy. It's a nice example of how to use the Attribute class to link between a data member and a DICOM tag. Here it is. Thanks John.

First, how to you use it. It's very simple. Use the Tag attribute above the class member like this:

[Tag(0x0010,0x0010)]

public string patient_name;

This just mapped the patient_name member to a DICOM Patient Name data element by using the tag (0010,0010).


Here's a test class for the DICOM Patient Module with patient name, patient id, patient birth date and patient sex. This test puts values into the module class, maps the class into a DCXOBJ and then creates a new instance of the module class and fills the data from the DCXOBJ. The test compares the values in the two instances.

using System;

using Microsoft.VisualStudio.TestTools.UnitTesting;

using GenericDICOM;

using rzdcxLib;

using System.Globalization;

namespace UnitTests

{

    [TestClass]

    public class DicomModuleTest

    {

        class PatientModule : DicomModule

        {

            [Tag(0x0010,0x0010)]

            public string patient_name;

            [Tag(0x0010, 0x0020)]

            public string patient_id;

            [Tag(0x0010, 0x0030)]

            public string _patient_birth_date;

            public DateTime patient_birth_date

            {

                set

                {

                    _patient_birth_date = value.ToString("yyyyMMdd");

                }

                get

                {

                    return DateTime.ParseExact(_patient_birth_date, "yyyyMMdd", CultureInfo.InvariantCulture);

                }

            }

            [Tag(0x0010,0x0040)]

            public string pateint_sex;

        }

        [TestMethod]

        public void TestDICOMFromTo()

        {

            PatientModule m = new PatientModule();

            m.patient_name = "A^B";

            m.patient_id = "PID123";

            m.patient_birth_date = new DateTime(2001, 02, 03);

            m.pateint_sex = "M";

            DCXOBJ o = m.ToDicomObject();

            PatientModule n = new PatientModule();

            n.FromDicomObject(o);

            Assert.AreEqual(m.patient_name, n.patient_name);

            Assert.AreEqual(m.patient_id, n.patient_id);

            Assert.AreEqual(m.patient_birth_date, n.patient_birth_date);

            Assert.AreEqual(m.pateint_sex, n.pateint_sex);

        }

    }

}

The DateTime type for patient birth date does require a little bit of dancing around it in order to format it properly. Maybe someone wants to contribute a generic class for it?

Here's the implementation of DicomModule class and the Tag Attribute class:

using System;

using rzdcxLib;

using System.Reflection;

namespace GenericDICOM

{

    ///

    /// The Tag attribute maps a member to a specific DICOM Data Element

    ///

    public class Tag : Attribute

    {

        public int tag;

        public Tag(ushort group, ushort element)

        {

            tag = group << 16 | element;

        }

    }

    ///

    /// A DICOM Module represents a set of DICOM Data Elelments

    ///

    public class DicomModule

    {

        public DicomModule()

        {

        }

        public DicomModule(DCXOBJ inObj)

        {

            FromDicomObject(inObj);

        }

        public DCXOBJ ToDicomObject()

        {

            DCXOBJ dicomObject = new DCXOBJ();

            FieldInfo[] fields = this.GetType().GetFields();

            foreach (FieldInfo f in fields)

            {

                Attribute[] attrs = System.Attribute.GetCustomAttributes(f);

                foreach (Attribute attr in attrs)

                {

                    if (attr is Tag)

                    {

                        DCXELM e = new DCXELM();

                        e.Init((attr as Tag).tag);

                        e.Value = f.GetValue(this);

                        dicomObject.insertElement(e);

                    }

                }

            }

            return dicomObject;

        }

        public void FromDicomObject(DCXOBJ dicomObject)

        {

            FieldInfo[] fields = this.GetType().GetFields();

            foreach (FieldInfo f in fields)

            {

                Attribute[] attrs = System.Attribute.GetCustomAttributes(f);

                foreach (Attribute attr in attrs)

                {

                    if (attr is Tag)

                    {

                        DCXELM e = dicomObject.GetElement((attr as Tag).tag);

                        if (e != null)

                            f.SetValue(this, Convert.ChangeType(e.Value, f.FieldType));

                    }

                }

            }

        }

    }

}

In the next post I'm going to take C# Generic Programming techniques a bit further and use the DicomModule class for performing DICOM Queries and Move instances using the DICOM Query/Retrieve Service.