Custom format edit text input android to accept credit card number

how to make edit text accept input in format

4digitnumber-4dignumber-4dignumber-4dignumber   

The code

text.addTextChangedListener(new TextWatcher() {
    int len = 0;
    String string ;
    @Override

    public void afterTextChanged(Editable s) {

        text.setOnKeyListener(new OnKeyListener()
        {   public boolean onKey(View v, int keyCode, KeyEvent event)
            {              
                    if (keyCode == KeyEvent.KEYCODE_DEL)
                    {

                    }
                    else{

                        string = text.getText().toString();
                        len = string.length()+1;
                        if(len%5==0){text.append("-");}

             }

                return false;      }   });
    }
});

works fine upon adding, but deleting or editing causes problem.