Add new property to existing object - c#

When both 'if' condition is satisfied, I want Start to be added to the same DataList along with value and time.

public List<object> DataList = new List<object>();

if(somecondition)
{     
    DataList.Add(new { Value = Value, Time = time}); // assume this is DataList[0]
    //var start = null;
    //DataList.Add(new { Value = Value, Time = time, Start = start}); 
}

if(somecondition)  
{
    -> how do I add `start` to DataList[0] here.
    //DataList.Add(new { Start = start });
    //DataList[0]?.Start  = start;   
}

Later, when I use DataList, it should contain values from both if condition. Thank you.

Here are two options.

Use inheritance:

void Method()
{
	/* init variables */

	if (someCondition)
	{
		DataList.Add(new Data() { Value = Value, Time = time });
	}
	else if (someOtherCondition)
	{
	    DataList.Add(new DataWithStart() { Value = Value, Time = time, Start = start });
	}
}

public List<Data> DataList = new List<Data>();

public class Data
{
	public string Value;
	public string Time;
}

public class DataWithStart : Data
{
	public string Start;
}

Or, use ExpandoObject:

void Method()
{
	/* init variables */

	dynamic data = new System.Dynamic.ExpandoObject();

	if (someCondition)
	{
		data.Value = Value;
		data.Time = time;
	}
	
	if (someOtherCondition)
	{
	    data.Start = start;
	}
	
	DataList.Add(data);
}

public List<System.Dynamic.ExpandoObject> DataList = new List<System.Dynamic.ExpandoObject>();

using System.Collections.Generic;
using System.Dynamic;

List<dynamic> DataList = new List<dynamic>();

dynamic data1 = new ExpandoObject();

if (someCondition)
{
    data1.Value = Value;
    data1.Time = time;
}

if (someCondition)
{
    data1.Start = start;
}

DataList.Add(data1);

you can use ExpandoObject to solve in simplest way.