Validation allow only number and characters in edit text in android

Instead of using your "manual" checking method, there is something very easy in Android:

InputFilter filter = new InputFilter() { 
    public CharSequence filter(CharSequence source, int start,
                               int end, Spanned dest, int dstart, int dend) { 

        for (int i = start;i < end;i++) { 
            if (!Character.isLetterOrDigit(source.charAt(i)) && 
                !Character.toString(source.charAt(i)).equals("_") && 
                !Character.toString(source.charAt(i)).equals("-")) 
            { 
                return ""; 
            } 
        } 
        return null; 
    } 
}; 

edittext.setFilters(new InputFilter[] { filter }); 

Or another approach: set the allowed characters in the XML where you are creating your EditText:

<EditText 
  android:inputType="text" 
  android:digits="0,1,2,3,4,5,6,7,8,9,*,qwertzuiopasdfghjklyxcvbnm,_,-" 
  android:hint="Only letters, digits, _ and - allowed" />

This can be useful, especially if your EditText should allow diacritics (in my case, Portuguese Diacritic):

<EditText
   android:digits="0123456789AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZzÁáÂâÃãÀàÇçÉéÊêÍíÓóÔôÕõÚú"
/>

<EditText 
  android:inputType="text" 
  android:digits="0,1,2,3,4,5,6,7,8,9,*,qwertzuiopasdfghjklyxcvbnm,_,-" 
  android:hint="Only letters, digits, _ and - allowed"
/>

the above code will also include , additionally to avoid , use the following code

<EditText 
  android:inputType="text" 
  android:digits="0123456789qwertzuiopasdfghjklyxcvbnm_-"
  android:hint="Only letters, digits, _ and - allowed"
/>

A solution similar to the android:digits="0123456789*", is to use this:

EditText etext = new EditText(this);
etext.setKeyListener(DigitsKeyListener.getInstance("0123456789*"));

An added bonus is that it also displays the numeric keypad.