Data Controls :: Add Dynamic Rows In GridView With TextBox And Keep Edited GridView Row Data On Post Back

I have 3 textboxes , 1 dropdown , 1 Button and 1 gridview .

Textboxes ID are :ACode , ADesc , ASeq
DropDown ID is :CPhase
Button ID is :AddRowBTN
GridView ID is :PhasesTempGrid

Now whats the story is ?After adding some data into textboxes , when a user clicks ADDRow BTN , that data gets saved into datatable , then that datatable gets binded to gridview and it shows my textboxes data in it .

What i want to achieve ?In my gridview i am use templateField and inside that template field there are textboxes ( Let the users edit the row without clicking any button ) .

Take an example of dummy data and problem persisting in there :for e.g i put some data in textboxes :ACode = "ABCD"ADesc = "EFGH"ASeq = "HIJK"Then i click Add BTN , it saves the data in datatable and show in gridview , now if i do this in gridview :ACode = "Edited ABCD"ADesc = "Edited EFGH too"ASeq = "WoW There"Then i click Add BTN , it removes the edited record in gridview and shows original data which had came earlier from textboxes :ACode = "ABCD"ADesc = "EFGH"ASeq = "HIJK"I don't want that to be done ... Simple is that user can enter data from textboxes , click the btn to submit into grid then he can edit the data like he want ... data must not get flashed , here's my coding i have done so far : 

public void AddNewData()
{
var dt = new DataTable();
if (ViewState["myDatatable"] != null)
{
dt = (DataTable) ViewState["myDatatable"];
}

[CODE]...

here i havent added dropdown combo in gridview but you can do it so that it will save my time (Bind it just the way PhaseDropDown have bind)...