passwords - how to animate the entry of a new character in passcode textview android? -

currently implementing custom textview passcode entry. i'm using custom transformation show last number entered so:

public class pincodepasswordtransformationmethod extends passwordtransformationmethod {  char passwordbullet = '\u26aa';  @override public charsequence gettransformation(charsequence source, view view) {     return new passwordcharsequence(source); }  private class passwordcharsequence implements charsequence {     private charsequence msource;      public passwordcharsequence(charsequence source) {         msource = source; // store char sequence     }     public char charat(int index) {         if(index != msource.length()-1)             return passwordbullet;         else             return msource.charat(index);      }     public int length() {         return msource.length(); // return default     }     public charsequence subsequence(int start, int end) {         return msource.subsequence(start, end); // return default     } } } 

and apply on textview so:

mtextview.settransformationmethod(new pincodepasswordtransformationmethod()); 

right each letter appears instantly when inputed. how can animate changes entry of new pin number , change of second last number password bullet character animated?