[C#] How to write a generic yield return WaitForCondition with an expression as argument ?

Question

I wondered how one could write something like a yield return new WaitForCondition which allows you to wait until a condition is matched. I thought about making it with a helper function and a while - loop but I am not very satisfied with it, since it requires an unqiue WaitForCondition for each usage, as well as reference to a field and it does not allow expressions, like in if - statements, they are converted into a value, not preserving the expression as is.

In the end, I would like to be able to do something like this:

 public class MyClass{
     bool myBool = false;
     public IEnumerator MyWait(){
         yield return new WaitForCondition(myBool == true);
         // doSomething
     }
 }

I do know that in this example, I could instead write it similar to the accepted solution to this question: Waiting for Input via Coroutine

However, on purpose, I would like to require a bool expression as argument, no matter whether it is yield return new WaitForCondition( b == true );or yield return StartCoroutine(WaitForCondition(b == true));The examples might be misleading in terms of usability, imagine more complex bool expressions.

How would I achieve this ? I do know there are workarounds using Properties, but I would like to force this way. The main problem for me is preserving the expression as is instead of converting it to a value, as one is waiting for a condition to be matched, hence requiring to continuously checking for it.

Answer 1

Best Answer

Answer by jdean300 · Feb 10, 2017 at 08:52 PM

This already exists: https://docs.unity3d.com/ScriptReference/WaitUntil.html

Add comment · Show 2 · Share

jdean300 · Feb 10, 2017 at 09:09 PM 1

Share

Just to explain things a bit more - you cannot pass a statement like b == true into a function and expect it to be evaluated multiple times - the statement is evaluated once and then given to the function. If you want a function to act based on some passed in argument that needs to be evaluated multiple times, you have to pass a lambda.

A lambda is fancy speak for a function. $$anonymous$$ore precisely it is a function with an execution context(local variables and such) wrapped up into one. What WaitUntil does is take a lambda that you give it that returns a bool and calls it every frame. When it returns true, WaitUntil breaks.

Here is an example of using WaitUntil with a typical function (alan$$anonymous$$emp already posted a lambda example):

 private IEnumerator LookAt$$anonymous$$e() {
   // pass a function to WaitUntil
   yield return new WaitUntil(BIsTrue);
 }
 
 // this function will be called by WaitUntil every frame
 private bool BIsTrue() { return b == true; }

Ardenian jdean300 · Feb 14, 2017 at 12:46 PM 0

Share

Thank you very much! I hanged myself a bit with the term "condition", wondered why Unity would not have something like this as default. Great to know this exists! Also, a great thank you for your explanation!

Answer 2

Answer by alankemp · Feb 10, 2017 at 08:52 PM

You can use WaitUntil to do this:

 yield return new WaitUntil( () => b == true );

Add comment · Show 1 · Share

Ardenian · Feb 14, 2017 at 12:47 PM 0

Share

Thank you!

Answer 3

Answer by dan_ginovker · Feb 16 at 09:42 AM

If you're like me and want a custom implementation of WaitUntil or WaitForSeconds, check out CustomYieldInstruction:

https://docs.unity3d.com/ScriptReference/CustomYieldInstruction.html

https://forum.unity.com/threads/writing-a-custom-class-yieldinstruction-to-wait-for-frames-or-seconds-depending-on-the-class-params.448925/

Add comment · Share

[C#] How to write a generic yield return WaitForCondition with an expression as argument ?

3 Replies

Your answer

Follow this Question

Related Questions