Explanation :

Construction Injection is a technique to avoid unnecessary implementations. Check this with some practical scenarios. 

Here i added one interface component with some property declarations.

public interface INewemp
    {
        string EmpID { get; set; }
        string EmpName { get; set; }
        string EmpAddress { get; set; }
        DateTime DateofJoining { get; set; }
    }

added one more interface component with one more additional property declaration.

public interface IOldemp
   {
       string EmpID { get; set; }
       string EmpName { get; set; }
       string EmpAddress { get; set; }
       DateTime DateofJoining { get; set; }
       DateTime DateofReleaving { get; set; }
   }

Check the above two interface components.  only 'DateofReleaving' property added to IOldemp interface and remains same. now lets come to implementation.

  public class Employee : IOldemp, INewemp
    {
 
}

Now we got big complexity between properties.
Example : Employee.EmpID refers to IOldemp component or INewemp component ? In this situations developer may get trouble.

  

To overcome this problem lets simplify our interface declarations as like below

public interface INewemp
   {
       string EmpID { get; set; }
       string EmpName { get; set; }
       string EmpAddress { get; set; }
       DateTime DateofJoining { get; set; }
   }

and

public interface IOldemp : INewemp
   {
       DateTime DateofReleaving { get; set; }
   }

no need to declare redundant properties in every interface components and good enough to implement IOldemp like below

public class Employee : IOldemp
    {
 
}

and you can get all INewemp reference from IOldemp with help of constructor Injection.

public class ConstructorInject
    {
        IOldemp OldEmpData = new Employee();
        public INewemp NewEmpData;
 
        public ConstructorInject()
        {
            NewEmpData = OldEmpData;
        }
    }

INewemp receiving reference from IOldemp in  ConstructorInject class constructor.

Test INewemp reference now

class Program
    {
        static void Main(string[] args)
        {
            var request = new ConstructorInject();
            var ActualResult = request.NewEmpData;
            Console.WriteLine("Actual values from Formal Object refrence");
            Console.WriteLine(ActualResult.EmpID);
            Console.WriteLine(ActualResult.EmpName);
            Console.WriteLine(ActualResult.EmpAddress);
            Console.Read();
 
        }
    }

So we no need implement all Interfaces and their properties. We can Inject it from class constructor.