UI sizeDelta.y return 0 after instantiation

Questions & Answers
1

This problem has been buggering be for quite some while. I have found a solution, bet it’s not as clean as i’d want.

Here are examples.

private void Start() {
    GameObject node = (GameObject)Instantiate(contentPrefab);

    RectTransform rectComponent = node.GetComponent<RectTransform>();

    Debug.Log(rectComponent.sizeDelta.y.ToString()); //prints 0 ?
}


private IEnumerator Start() {
    GameObject node = (GameObject)Instantiate(contentPrefab);

    RectTransform rectComponent = node.GetComponent<RectTransform>();

    yield return new WaitForSeconds(0.1f); //wait for some small time
    Debug.Log(rectComponent.sizeDelta.y.ToString()); //prints actual value, not 0
}

Looks like UI elements are not updated on instantiation, but in fact left for update on next iterations.

Has anyone tried any workarounds, without using any update methods?

2

Solution is to wait a frame before UI element is actually initiated and positioned.
That can be done by:

yield return null;

yield return new WaitForEndOfFrame();

or set the element dirty and process it in fixedupdate.