Selectable.navigation

public UI.Navigation navigation ;

Description

The Navigation setting for this selectable object.

using UnityEngine;
using System.Collections;
using UnityEngine.UI; // Required when Using UI elements.

public class ExampleClass : MonoBehaviour
{
    public Button button;

    void Start()
    {
        //Set the navigation to the default value. ("Automatic" is the default value).
        button.navigation = Navigation.defaultNavigation;
    }
}