[Solved] Enabling/Disabling Canvas Creates GC Alloc

Hello all. I have come across a bit of a problem. I am trying to reduce GC Alloc in my game. I am using Unity 2020.3.3f1. So I have been deep profiling and fixing any GC Alloc produced. I have come across a problem where I am unable to reduce GC Alloc by enabling and disabling a canvas for hiding some images.

Everytime I enable or disable a canvas it creates a GC Alloc of 364B in editor and 256B in build. This isn't created everyframe but is created everytime the player switches weapon because I have linked the weapon switch and crosshair together so that when the player switches a weapon a different crosshair canvas is enable or disabled.

So my questions are, is it possible to enable and disable a canvas without creating GC Alloc? If possible then how to do it?

Sharing my code, profiling pic and canvas hierarchy pic to give much clearer picture.

Code (CSharp):

1. using GiantMech.Weapons;
2. using UnityEngine;
3.  
4. namespace GiantMech.UIs
5. {
6.     public class IconHelper : MonoBehaviour
7.     {
8.         [Header("IconHelper Local Properties")]
9.         [SerializeField] private Canvas _iconCanvas;
10.  
11.         private IWeapon _weapon;
12.  
13.         private void Awake()
14.         {
15.             TryGetComponent(out _weapon);
16.             _weapon.RegisterIcon(SetIcon);
17.         }
18.  
19.         /// <summary>
20.         /// This method hides/shows the icon.
21.         /// </summary>
22.         /// <param name="isShow">True means to show the icon, false otherwise,
23.         ///                      of type bool</param>
24.         public void SetIcon(bool isShow) => _iconCanvas.enabled = isShow;
25.     }
26. }

Line 16, weapon.RegisterIcon(SetIcon), stores the SetIcon(bool) method in a delegate for the _weapon to call whenever there is a weapon switch.



The above picture is of the deep profilling I did in the editor. I have highlighted the part where my code starts the GC Alloc and from there it is all Unity.



The above picture is the hierarchy where the canvas is located. I have highlighted the canvas and inside it are two images. G O means Game Object. This means that the weapon contains the canvas.

I have tried by removing the canvas from the weapon game object and placing it outside like a normal static canvas. I have also tried to enable/disable the image components only in the canvas but didn't work. I have also tried to enable/disable the canvas gameobject to see what happens, which is a no no, and wasn't surprised by the gc alloc byte in this approch.

When working with Unity's UI I always follow Unite 2016 - Let's Talk (Content) Optimization and Some of the best optimization tips for Unity UI. Those two links always had the answers that I am looking for but unfortunately in this case I can't find any answer to fix this.

Any help/information will be much appreciated.

K Out!

 

Alright guys I have solved the issue. Another idea came to me right after posting this thread. I am now getting 0B for enabling and disabling canvases in build. Let me share what I did.



I have one main canvas, which I have highlighted. This canvas contains two more canvases which contains one image each. The sub canvases are always enabled and are never disabled. Only the main canvas, IconCanvas, is enabled/disabled. This now does not generate any GC Alloc in build but in editor it shows 0.7KB is created, which are PreUpdate.IMGUISendQueuedEvents(368B) and GUI.Repaint(368B), but that is not due to my code or enabling/disabling the canvases. This is probably some editor GC Alloc being created.

This was mentioned in the linked I provided but for some reason this just escaped my mind. I hope this helps anyone else who may come across this problem.

K Out!