Playing an animation from code

I'm trying to play an animation from code using the following lines:

Code (CSharp):

1. Animator mAnim = this.GetComponent<Animator> ();
2. ...
3. mAnim.Play("Ui_In", 0);

But instead of playing the animation, the following warning is issued:

A screenshot of the states in the animation controller is attached.
What could be the cause of this problem? Thanks!

 

I think this will help you:
https://unity3d.com/learn/tutorials/modules/beginner/animation/animator-scripting

 

So there is no way to do this without transitions and triggers?
Seems somewhat overcomplicated...

 

What I meant is... try this:

Code (CSharp):

1.     Animator anim;
2.     int yourAwesomeAnimation = Animator.StringToHash("Ui_In");
3.  
4.  
5.     void Start ()
6.     {
7.         anim = GetComponent<Animator>();
8.         PlayYourAwesomeAnimation();
9.     }
10.  
11.     void PlayYourAwesomeAnimation()
12.     {
13.        anim.Play(YourAwesomeAnimation);
14.     }