trouble with UI Text.

After upgrade to Unity 5.5.0b4, I have problem with the UI Text, I just upgrade to 5.5.0b7 and i got the same problem with UI Text.
// Include UI library.
using UnityEngine.UI;
*
//Create new UI Text
public Text newText;
*
//set value to newText but I cannot found text, It disappears after I update to Unity 5.5.*
newText.text = "blablabla";

//Moreover, I cannot drag and drop UI text into newText in the inspector window.

I update back to version 5.4 and everything works well again.

 

Crash for IOS with a simple code (version 5.5.0b7)
Run ok on Editor

Text t = GetComponent<Text> ();
t.text = "123";