c# - Why does this generic method require T to have a public, parameterless constructor?

Question

public void Getrecords(ref IList iList,T dataItem) 
{ 
  iList = Populate.GetList<dataItem>() // GetListis defined as GetList<T>
}

dataItem can be my order object or user object which will be decided at run time.The above does not work as it gives me this error The type 'T' must have a public parameterless constructor in order to use it as parameter 'T' in the generic type

Answer 1

public void GetRecords<T>(ref IList<T> iList, T dataitem)
{
}

What more are you looking for?

To Revised question:

 iList = Populate.GetList<dataItem>() 

"dataitem" is a variable. You want to specify a type there:

 iList = Populate.GetList<T>() 

The type 'T' must have a public parameterless constructor in order to use it as parameter 'T' in the generic type GetList:new()

This is saying that when you defined Populate.GetList(), you declared it like this:

IList<T> GetList<T>() where T: new() 
{...}

That tells the compiler that GetList can only use types that have a public parameterless constructor. You use T to create a GetList method in GetRecords (T refers to different types here), you have to put the same limitation on it:

public void GetRecords<T>(ref IList<T> iList, T dataitem) where T: new() 
{
   iList = Populate.GetList<T>();
}