为什么当我在 UI 元素上右键单击 NOT 时编译器会出错

Question

My compiler gives an error ArgumentOutOfRangeException in the file List.cs when I click on the empty space but if I click on the UI elements it's doesn't gives an error. But how it gives an error if I have a check

if (results != null)

There is my code :

public void Update()
{

    if (Input.GetKey(KeyCode.Mouse1))
    {
        eventData = new PointerEventData(eventSystem);
        eventData.position = Input.mousePosition;

        List<RaycastResult> results = new List<RaycastResult>();

        _raycaster.Raycast(eventData, results);

        if (results != null)
        {
            if (results[0].gameObject.tag == "ItemIcon")
            {
                if(currentMenu != null)
                {
                    Destroy(currentMenu);
                }
                currentMenu = Instantiate(SplitMenu, transform);
            }
        }
    }
} 

Answer 1

My best guess is that you are checking that results != null, but you are not checking if results actually has any elements in it. So using results[0] on an empty array results in the ArgumentOutOfRangeException you are seeing.

Adding && results.Any() to the if check should resolve it.

Answer 2

最好的选择：我们需要使用results.Count != 0而不是null 。

Answer 3

1.    List<RaycastResult> results = new List<RaycastResult>();

     _raycaster.Raycast(eventData, results);

2.    if (results != null)
    {
3.        if (results[0].gameObject.tag == "ItemIcon")

Line 1 initialises results , so that check on line 3 will never be false. Just because results is initialised, doesn't mean it has any entries in it, so line 3 will give an error if there are no results.

As others have pointed out, line 2 should be:

if(results.Any())

.Any() is better that .Count > 0 because it implies the intent that 'something is in the list', rather than 'the count is greater than 0'.