How to enable text when listening with "addTextChangedListener" and "Character.isLetterOrDigit(s.charAt(i))"

I disable a button when the user inserts non LetterOrDigit and enable it when a user inserts LetterOrDigit.

The problem I'm having is that it enables it too even when the user inserts a letter after a non LetterOrDigit. But I want to only enable when he deletes the non LetterOrDigit character.

My Code

 name1.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {
            }
            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
            }
            @Override
            public void afterTextChanged(Editable s) {
                for (int i = 0; i < s.length(); i++) {
                    if(name1.getText().toString().length()>16)
                    {
                        register.setClickable(false);
                        mistakeusername.setErrorEnabled(true);
                        mistakeusername.setError("You cant insert more then 16 characters");
                    }else {
                        if (!(Character.isLetterOrDigit(s.charAt(i))||Character.toString(s.charAt(i)).equals("_")))
                        {
                            register.setClickable(false);
                            mistakeusername.setErrorEnabled(true);
                            mistakeusername.setError("Only allowed Digit, Number or '_'");
                        }else{
                            register.setClickable(true);
                            mistakeusername.setErrorEnabled(false);
                            mistakeusername.setError("");
                        }
                    }
                }
            }
         });

i think your problem is that you should break from for after your if(!(Character.isLetterOrDigit(s.charAt(i))||Character.toSt‌​ring(s.charAt(i)).eq‌​uals("_"))) is true.

try this:

 name1.addTextChangedListener(new TextWatcher() {
        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {
        }
        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
        }
        @Override
        public void afterTextChanged(Editable s) {
            for (int i = 0; i < s.length(); i++) {
                if(name1.getText().toString().length()>16)
                {
                    register.setClickable(false);
                    mistakeusername.setErrorEnabled(true);
                    mistakeusername.setError("You cant insert more then 16 characters");
                }else {
                    if (!(Character.isLetterOrDigit(s.charAt(i))||Character.toString(s.charAt(i)).equals("_")))
                    {
                        register.setClickable(false);
                        mistakeusername.setErrorEnabled(true);
                        mistakeusername.setError("Only allowed Digit, Number or '_'");
                        break;
                    }else{
                        register.setClickable(true);
                        mistakeusername.setErrorEnabled(false);
                        mistakeusername.setError("");
                    }
                }
            }
        }
     });