Using reflection, get an individual item from a property that is an object array

Question

0.00/5 (No votes)

See more:

I have a data set that is in a peculiar setup - an array of "column" classes with properties "Name", "DataType" and "Values"

The latter property is an array of values e.g.

C#

public partial class UsageColumn  {

    private string nameField;

    private string dataTypeField;

    private object[] valuesField;


    public string Name {
        get {
            return this.nameField;
        }
        set {
            this.nameField = value;
        }
    }

    public string DataType {
        get {
            return this.dataTypeField;
        }
        set {
            this.dataTypeField = value;
        }
    }

    public object[] Values {
        get {
            return this.valuesField;
        }
        set {
            this.valuesField = value;
        }
    }

    }
}

I am currently turning this into a .NET collection thus:-

public static List<TRecord> ConvertResultToList<TRecord>(object[] columns, int rowCount) where TRecord : DTO.IDataScopeDTOClass
{
    List<TRecord> ret = new List<TRecord>();

    // The object that we got in columns should have a property called Name and a property called DataType and Values[]
    if (rowCount > 0)
    {
        if (columns.Count() > 0)
        {
            System.Reflection.PropertyInfo piName = columns[0].GetType().GetProperty(@"Name" );
            System.Reflection.PropertyInfo piDataType = columns[0].GetType().GetProperty(@"DataType");
            System.Reflection.PropertyInfo piValues = columns[0].GetType().GetProperty(@"Values");

            System.Reflection.ConstructorInfo ciTarget = typeof(TRecord).GetConstructor(Type.EmptyTypes );


            for (int i = 0; i < rowCount ; i++)
            {
                TRecord newValue = (TRecord)ciTarget.Invoke(null);
                foreach (var thisColumn in columns)
                {
                    string name = piName.GetValue(thisColumn).ToString();
                    string dataType = piDataType.GetValue(thisColumn).ToString();
                    object[] value = (object[])piValues.GetValue(thisColumn);
                    newValue.SetProperty(name, dataType, value[i]);
                }
                ret.Add(newValue);
            }

        }


    }

    return ret;
}

However the line object[] value = (object[])piValues.GetValue(thisColumn); is copying the whole array every time. How do I just get the value at index [i] ?

Posted 4-Jul-14 0:11am

Duncan Edwards Jones

Updated 4-Jul-14 0:28am

v2

Add a Solution

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Richard Deeming · Accepted Answer · 2014-07-04T02:40:00

It's not copying the array; it's just getting a reference to the existing array.

You could retrieve a single value using reflection, but that would almost certainly be slower than casting the value to an array and accessing it directly:

C#

System.Reflection.MethodInfo miGet = piValues.PropertyType.GetMethod("Get");
...
object values = piValues.GetValue(thisColumn);
object value = miGet.Invoke(values, new object[] { i });
newValue.SetProperty(name, dataType, value);

Other comments:

A call to GetType() is slow; you should cache and re-use the result of columns[0].GetType():

C#

Type columnType = columns[0].GetType();
System.Reflection.PropertyInfo piName = columnType.GetProperty(@"Name" );
System.Reflection.PropertyInfo piDataType = columnType.GetProperty(@"DataType");
System.Reflection.PropertyInfo piValues = columnType.GetProperty(@"Values");

You can avoid calling the TRecord's constructor via reflection by adding a new() constraint to the type parameter:

C#

where TRecord : DTO.IDataScopeDTOClass, new()
...
TRecord newValue = new TRecord();