Why is spacebar causing Unity to fire last OnClick() event

Question

I have a turn based roguelike with input issues that are driving me nuts.

I use the Unity Input/GetAxis() for keyboard input. I recently added a skill bar with clickable buttons that pass an int parameter to a simple class when clicked.

The problem I am having is that the OnClick() event, on the last button that was clicked, fires whenever the SPACE bar is pressed.

What could cause this? I do not have space set on any of the input Axes (I did originally and both the axes attached to SPACE and the OnClick() would fire)

Edit: The code is below. It is called by the OnClick() handler on the button in the inspector. If you run the project and press SPACE nothing happens. Then if you click a button the Debug.Log fires. Then press SPACE again and the debug fires again with the same button number as was last clicked.

public class SkillClickNotifier : MonoBehaviour
{
    [HideInInspector]
    public int SkillClicked;

    public void ButtonClicked(int skill)
    {
        Debug.Log("Button Clicked: "+ skill);
        // SkillClicked = skill;
        // GameManager.Notifications.PostNotification(this, "SkillClicked");
    }
}

Answer 1

I found the answer and am answering it myself in the hope it will help someone in the future.

In the Unity Button control there is a property called Navigation that defaults to Automatic. This is to allow keyboard navigation and was causing my issue when the Space bar was pressed. The correct setting for me was None.

Answer 2

When you click on the button, there will then be a color surrounding it, telling the user that the button is now the selected UI item. Hitting Space at this point "activates" the UI item.

This will not necessarily solve the issue, but clicking off the screen will remove the selection, and so when you'll press Space again, the OnClick event will not fire.

Answer 3

For those who are using the UI Toolkit:

var root = GetComponent<UIDocument>().rootVisualElement;

root.RegisterCallback<NavigationSubmitEvent>((evt) =>
{
    evt.StopPropagation();
}, TrickleDown.TrickleDown);

There's also a Cancel- and MoveEvent which might interest you.