Bug Root canvas invalid RectTransform.sizeDelta

I have a root canvas (the most top object that have canvas component in hierarchy) , and i have canvas scaler with specification :

• UI Scale Mode = Scale With Screen Size
• Screen Match Mode = Expand

Then i check the root canvas RectTransform size delta with this script

Code (CSharp):

1.  
2. public int oldscreenwidth = 0;
3. public int oldscreenheight = 0;
4. public GameObject rootcanvas;
5. void awake() {
6. oldscreenwidth = Screen.width;
7. oldscreenheight = Screen.height;
8. rootcanvas = this.gameObject.GetComponentInParent<Canvas>().rootCanvas.gameObject;
9. }
10. void update() {
11. if(Screen.width != oldscreenwidth || Screen.height != oldscreenheight ) {
12. Debug.Log(" rootcanvas SizeDelta when screen resolution changed : " + rootcanvas.GetComponent<RectTransform>().sizeDelta);
13. oldscreenwidth = Screen.width;
14. oldscrenheight = Screen.height;
15. } else {
16. Debug.Log(" rootcanvas SizeDelta in normal condition : " + rootcanvas.GetComponent<RectTransform>().sizeDelta);
17. }
18. }
19.  

I noticed that when the screen resolution changed , at that exact frame , root canvas size delta will "blink" to wrong size which will be corrected in the next frame. This is annoying as i was wondering what was wrong with my UI script until i found this bug.

Code (CSharp):

1. LayoutRebuilder.ForceRebuildLayoutImmediate(rootcanvas.GetComponent<RectTransform>());

I also have tried force rebuild before the Debug.Log but it seems like the problem cannot be fixed at that frame , the problem fixes itself the next frame after screen resolution changed.