[unity3d] cannot correctly obtain the attribute value of recttransform, resulting in calculation error

UGUI obtain RectTransform There are too many pits in some attributes of , Record the pits that bloggers have stepped on ：

1. because ContentSizeFitter Component causes incorrect acquisition UI The width and height of

Refer to the practice of xuanyusong great God ：Unity3D Research Institute of ContentSizeFitter Synchronous immediate response callback

public static Vector2 GetPreferredSize (RectTransform rect, ContentSizeFitter fitter) {
    
   if (rect == null || fitter == null) {
    
       return Vector2.zero;
   }
   LayoutRebuilder.ForceRebuildLayoutImmediate (rect);
   return new Vector2 (HandleSelfFittingAlongAxis (0, fitter, rect), HandleSelfFittingAlongAxis (1, fitter, rect));
}

// Get width and height 
private static float HandleSelfFittingAlongAxis (int axis, ContentSizeFitter fitter, RectTransform rect) {
    
    ContentSizeFitter.FitMode fitting = (axis == 0 ? fitter.horizontalFit : fitter.verticalFit);
    if (fitting == ContentSizeFitter.FitMode.MinSize) {
    
        var size = LayoutUtility.GetMinSize (rect, axis);
        return size;
    } else {
    
        var size = LayoutUtility.GetPreferredSize (rect, axis);
        return size;
    }
}

2. Canvas Prompt on ‘some values driven by canvas’ Can't get Canvas Correct width and height

If you want to get Canvas Of RectTransform.rect.width / RectTransform.rect.height Be careful when this prompt appears ,rect It is likely that both width and height are zero , I guess it's also because RectTransform It takes a frame to set the correct width and height RectTransform in , So what bloggers do is ：
Start a collaborative process , Keep checking RectTransform.rect.width / RectTransform.rect.height, When both values are greater than zero, execute your callback

Be careful , If there is a need to convert the world coordinates of the object to a Canvas Under the UI Coordinates , We have to wait Canvas Of rect Both width and height are greater than zero , Otherwise, it is also wrong , Here is the conversion code ：

public static Vector3 WorldToUGUIPosition (Camera worldCam, Vector3 worldPos, Camera uiCamera, RectTransform uiRect) {
    
   	var pos = worldCam.WorldToScreenPoint (worldPos);
    Vector2 result;
    RectTransformUtility.ScreenPointToLocalPointInRectangle(uiRect, pos, uiCamera, out result);
    return result;
}