UI timer without Garbage Collection possible?

I have a TMPro UI timer (timeText) updating every frame, using TimeSpan.

Code (CSharp):

1.     private void UpdateTime()
2.     {
3.         timer += Time.deltaTime;
4.         timeSpan = TimeSpan.FromSeconds(timer);
5.  
6.         timeToDisplay = timeSpan.ToString(@"mm\:ss\:ff");
7.         timeText.text = timeToDisplay;
8.     }

This generates 11 calls and 0.9kb of GC / frame.
I've tried other methods like calculating minutes, seconds and milliseconds separately, then building the string, but that has even much poorer results as far as calls and GC goes.

Has anyone a more efficient solution that does not generate GC?

 

It's impossible to create a new string and not generate garbage, and TextMeshPro may very well be doing something with the string you assign as well to generate even more garbage. Your best bet is to only update it as frequently as needed -- I doubt you need the time updated every single frame?

 

You can try the ultra-trashy way: Instantiate 60 texts for 0-59 minutes, instantiate 60 for 0-59 seconds, etc. Then enable/disable the combination you need instead of changing the text. I'm not sure how much GC you'd save from it, but at least the string allocation is gone, and probably the text mesh generation is gone. You'll still get a canvas rebuild I guess? Not too sure .

 

You can totally make a new string without allocating.
Well, not a "string" directly, but you can definitely display changing text with numbers and stuff .


Just use SetText() on the tmp text. It has specialized handling for floats and supports basic formatting (just decimal digits, that's all, but it's enough).
There are multiple overloads for it, take a look.

It 100% does not allocate anything to build the new string.

Another alternative would be using a string builder (however that might allocate some small strings sometimes when dealing with number to text formatting).

 

Actually came up with something similar, which is perhaps overkill, but works super well.
Made a static array pool of intToStrings from 0 to 99 in awake, and the value of the array is then called via timeSpan.
After generation, no further garbage at runtime, only 1 call.

Here's the example for seconds (I use the same path for minutes and milliseconds):

Code (CSharp):

1.     private void UpdateTime()
2.     {
3.         timer += Time.deltaTime;
4.         timeSpan = TimeSpan.FromSeconds(timer);
5.         timeText.SetText(TimerStringsPool.GetNumberString(timeSpan.Seconds));
6.     }

 

I had no idea about the SetText()! That's on the textmeshpro text instead of UGUI text?

 

Text Mesh Pro allows you to give it a char array, so you can just do that. I've got GC-free strings like that.

Essentially, to show the time 12:45, you do:

Code (csharp):

1. chars[0] = '1';
2. chars[1] = '2';
3. chars[2] = ':';
4. chars[3] = '4';
5. chars[4] = '5';
6.  
7. textMeshProThing.SetCharArray(chars);

that won't allocate anything for the string generation. I also seem to remember that you can null-terminate strings using that apporach, so if you set chars[n] to '\0', no chars from n or later will be displayed.

Turning time into chars and putting them into the correct slots is an exercise left to the reader.

 

Just in case anyone is looking for a copy and paste solution - here's some seconds to char array code for format 0:00.000

Code (CSharp):

1.     private void SecondsToCharArray(float timeInSeconds, char[] array) {
2.         int minutes = (int)(timeInSeconds / 60f);
3.         array[0] = (char)(48 + (minutes % 10));
4.         array[1] = ':';
5.  
6.         int seconds = (int)(timeInSeconds - minutes * 60);
7.         array[2] = (char)(48 + seconds / 10);
8.         array[3] = (char)(48 + seconds % 10);
9.         array[4] = '.';
10.  
11.         int milliseconds = (int)((timeInSeconds % 1) * 1000);
12.         array[5] = (char)(48 + milliseconds / 100);
13.         array[6] = (char)(48 + (milliseconds % 100) / 10);
14.         array[7] = (char)(48 + milliseconds % 10);
15.     }

 

How about changing the sprite of a Image? There is no string involved in this method.