How to set focus of a dialog window?

Question

I have a dialog, which, when pops up, requests input from the user. How can I set the window up that the focus is on the InputField of the new window (i.e. the caret stands in the InputField), so that when the user starts typing, it is immediately registered by the field? At the moment, I have to click inside the field first to make it the active control on screen.

DialogInput[{InputField["", String], Button["Ok", DialogReturn[]]}]

Answer 1

Since Input is a DialogInput, it seemed reasonable to peek into Input's structure to understand how the focus is set. After removing the ReadProtected attribute I've realized that there is no neat way to do it, as WRI itself has done the reposition of the focus via successive SelectionMove calls.

This example below is not the original but a modified version, as the original Input definition only includes one InputField but no other expressions (like a Button). Note that it is not documented that you can use Initialization in dialogs, moreover it is colored red by the syntax highlighter to suggest an invalid option.

DialogInput[{InputField["", String], Button["Ok", DialogReturn[]]},
 Initialization :> (FrontEndExecute[{
      FrontEnd`SelectionMove[#1, Before, Notebook, 
       AutoScroll -> False],
      FrontEnd`SelectionMove[#1, Next, Cell, 2, AutoScroll -> False],
      FrontEnd`SelectionMove[#1, Previous, CellContents, 
       AutoScroll -> False],
      FrontEnd`FrontEndToken[#1, "MovePreviousPlaceHolder"]
      }] &), ShowCellBracket -> True, Selectable -> True]

Answer 2

What's wrong with Input[""]?