Mecanim Trigger getting stuck in 'TRUE' state

Ultroman's answer is not 100% exact. The problem does not (always) occur when you trigger an animation that is currently being played. It does occur when you trigger an amination while a transition is still running.

Let's say you have 2 animations: A and B and 2 triggers: tA and tB, animation A plays when tA gets triggered and animation B plays when tB gets triggered. If you trigger tA animation A will start playing, but if you trigger tB before animation A has finished, tA won't be reset, it will remain true until animation A is played from begining to end. The same also happens if you trigger tA for a second time while animation A is still playing.

So, if for some reason you need to trigger tB and you are not sure if animation A has finished, you should use ResetTrigger, I didn't understand why the guys at Unity decided to include this funtion until I stumbled upon this problem.

To prevent this unwanted behaviour you should do something like this:

 animator.ResetTrigger("tA");
 animator.SetTigger("tB);

2021 update: Check out the answer above instead or follow this link: http://answers.unity.com/answers/977718/view.html

ORIGINAL ANSWER: I found out that there is a problem with Mechanim, if you try to trigger the same animation that is already running. I don't think it is built for that. It is a state-machine after all, so it makes sense that it should never trigger an animation that is already running.

You "simply" have to check if the animation you're starting is already running.

I've done these steps to ease my life:

1. Made one trigger for each of my animations, with the same name as the animation I want to trigger! (this is important, if you want to use the simple functions below)

2. Made a transition from "Any State" to each of my animations, and the only condition for each transition, is the matching trigger.

3. Then I made a PlayAnimation function, which checks if the animation is already running:

.

 public void PlayAnimation(string animationName){
     if (!_animator.GetCurrentAnimatorStateInfo(0).IsName(animationName))
         _animator.SetTrigger(animationName);
 }

...and here's one where you can control the layer you're checking:

 public void PlayAnimation(string animationName, int layer){
     if (!_animator.GetCurrentAnimatorStateInfo(layer).IsName(animationName))
         _animator.SetTrigger(animationName);
 }

The IsName() function checks if the string you pass it, is the name of the currently playing animation. If it isn't, I use the trigger with the same name. Simple.

This works for me.

The animations trigger instantly, though.

I don't know if this interrupts non-atomic animations.

EDIT: Since doing this, I somehow got my Animator working normally, so now I can just do:

 _animator.Play(animationName);

It doesn't screw up anymore, and I don't need to use triggers at all. And also, I can do this to restart the running animation from scratch, even if it is the same animation:

 _animator.Play(animationName, layer, 0.0f);

I don't know why, but this wasn't working yesterday. _animator.Play() just didn't do anything.

This is how I did in my game after reading the articles.

 string currentAnimation = null;

 void setAnimation(string stringInput){
     Animator anim =transform.GetComponent<Animator>();
     Debug.Log("Setting Anim to : " + stringInput);
     if(currentAnimation==stringInput){

     }else{
         if(currentAnimation!=null){
             anim.ResetTrigger(currentAnimation);
         }
         anim.SetTrigger(stringInput);
         currentAnimation=stringInput;
     }
 }

you need to turn on flag "can transition to self" in transition settings rollout.

For what it's worth, I've had this problem when setting the trigger while in a state that had no exit condition based on that trigger. The trigger was simply not consumed.