How to use EditText onTextChanged event when I press the number?

You can also try this:

EditText searchTo = (EditText)findViewById(R.id.medittext);
searchTo.addTextChangedListener(new TextWatcher() {
    @Override
    public void afterTextChanged(Editable s) {
        // TODO Auto-generated method stub
    }

    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {
        // TODO Auto-generated method stub
    }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {
        doSomething();
    } 
});

You have selected correct approach. You have to extend the class with TextWatcher and override afterTextChanged(),beforeTextChanged(), onTextChanged().

You have to write your desired logic in afterTextChanged() method to achieve functionality needed by you.

Here, I wrote something similar to what u need:

    inputBoxNumberEt.setText(".     ");
    inputBoxNumberEt.setSelection(inputBoxNumberEt.getText().length());
    inputBoxNumberEt.addTextChangedListener(new TextWatcher() {

        boolean ignoreChange = false;

        @Override
        public void afterTextChanged(Editable s) {
        }

        @Override
        public void beforeTextChanged(CharSequence s, int start,
                                      int count, int after) {
        }

        @Override
        public void onTextChanged(CharSequence s, int start,
                                  int before, int count) {
            if (!ignoreChange) {
                String string = s.toString();
                string = string.replace(".", "");
                string = string.replace(" ", "");
                if (string.length() == 0)
                    string = ".     ";
                else if (string.length() == 1)
                    string = ".  " + string;
                else if (string.length() == 2)
                    string = "." + string;
                else if (string.length() > 2)
                    string = string.substring(0, string.length() - 2) + "." + string.substring(string.length() - 2, string.length());
                ignoreChange = true;
                inputBoxNumberEt.setText(string);
                inputBoxNumberEt.setSelection(inputBoxNumberEt.getText().length());
                ignoreChange = false;
            }
        }
    });

put the logic in

afterTextChanged(Editable s) {
    string str = s.toString()
    // use the string str
}

documentation on TextWatcher