title: How to make users not to delete suffix in EditText?
body: <p>i create a form with an EditText that takes in input numberDecimal (i set <code>android:inputType="numberDecimal"</code> in related XML file) and i write the following activity that prevent inserting numbers with more than 2 decimal places (i used <code>.setFilters()</code>). In addition i set a suffix in the same EditText and i would avoid that users can delete this suffix, neither add some input after it. I mean that if users go at the end of the EditText and tries to press backspace button the cursor goes at the begin of the suffix " m" (including space).
  How to do that?</p>
  
  <pre><code>public class InputForm extends Activity {
      EditText inputField;
  
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.input_form);    
  
          inputField = (EditText) findViewById(R.id.editInput);
          inputField.setText(" m");
          inputField.setSelection(0);
  
          inputField.setFilters(new InputFilter[] {new DecimalDigitsInputFilter(2)});
  }
  
      public class DecimalDigitsInputFilter implements InputFilter {
          Pattern mPattern;
          public DecimalDigitsInputFilter(int digitsAfterZero) {
              mPattern = Pattern.compile("[0-9]+((\\.[0-9]{0," + (digitsAfterZero-1) + "})?)||(\\.)?");
          }
          @Override
          public CharSequence filter(CharSequence source, int start, int end, Spanned dest, int dstart, int dend) {
              int input_length = dest.length() - 2; // lenght of the input without " m"
  
              Matcher matcher = mPattern.matcher(dest.subSequence(0, input_length));
  
              if(!matcher.matches())
                  return "";
  
              return null;
          }
      }
  }
  </code></pre>