GUIUtility.keyboardControl

Description

The controlID of the control that has keyboard focus.

    // Click on the text field to see the id of the control.

    private var str : String = "A String!";
    function OnGUI() {
        str = GUILayout.TextField(str,10);
        Debug.Log("id: " + GUIUtility.keyboardControl);
    }

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    private string str = "A String!";
    void OnGUI() {
        str = GUILayout.TextField(str, 10);
        Debug.Log("id: " + GUIUtility.keyboardControl);
    }
}