EditText showing numbers with 2 decimals at all times

I would like to display the input of the EditText fields with two decimals at all times. So when the user enters 5 it will show 5.00 or when the user enters 7.5 it will show 7.50.

Besides that I would like to also show zero when the field is empty instead of nothing.

What I've got already is the inputtype set to:

android:inputType="number|numberDecimal"/>

Should I work with inputfilters here?

Sorry I still quite new to android / java...

Thanks for your help!

Edit 2011-07-09 23.35 - Solved part 1 of 2: The "" to 0.00.

With the answer of nickfox I was able to solve half of my question.

    et.addTextChangedListener(new TextWatcher() {
        public void afterTextChanged(Editable s) {}
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {}
        public void onTextChanged(CharSequence s, int start, int before, int count) {
            if(s.toString().matches(""))
            {
                et.setText("0.00");
                Selection.setSelection(et.getText(), 0, 4);
            } 
        }
    });

I'm still working on a solution for the other half of my question. If I found the solution I will post it here too.

Edit 2011-07-09 23.35 - Solved part 2 of 2: Change user input to a number with two decimals.

OnFocusChangeListener FocusChanged = new OnFocusChangeListener() {

    @Override
    public void onFocusChange(View v, boolean hasFocus) {
        if(!hasFocus){
            String userInput = et.getText().toString();

            int dotPos = -1;    

            for (int i = 0; i < userInput.length(); i++) {
                char c = userInput.charAt(i);
                if (c == '.') {
                    dotPos = i;
                }
            }

            if (dotPos == -1){
                et.setText(userInput + ".00");
            } else {
                if ( userInput.length() - dotPos == 1 ) {
                    et.setText(userInput + "00");
                } else if ( userInput.length() - dotPos == 2 ) {
                    et.setText(userInput + "0");
                }
            }
        }
    }

Here is something I use to for dollar input. It makes sure that there are only 2 places past the decimal point at all times. You should be able to adapt it to your needs by removing the $ sign.

    amountEditText.setRawInputType(Configuration.KEYBOARD_12KEY);
    amountEditText.addTextChangedListener(new TextWatcher() {
        public void afterTextChanged(Editable s) {}
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {}

        public void onTextChanged(CharSequence s, int start, int before, int count) {
            if(!s.toString().matches("^\\$(\\d{1,3}(\\,\\d{3})*|(\\d+))(\\.\\d{2})?$"))
            {
                String userInput= ""+s.toString().replaceAll("[^\\d]", "");
                StringBuilder cashAmountBuilder = new StringBuilder(userInput);

                while (cashAmountBuilder.length() > 3 && cashAmountBuilder.charAt(0) == '0') {
                    cashAmountBuilder.deleteCharAt(0);
                }
                while (cashAmountBuilder.length() < 3) {
                    cashAmountBuilder.insert(0, '0');
                }
                cashAmountBuilder.insert(cashAmountBuilder.length()-2, '.');
                cashAmountBuilder.insert(0, '$');

                amountEditText.setText(cashAmountBuilder.toString());
                // keeps the cursor always to the right
                Selection.setSelection(amountEditText.getText(), cashAmountBuilder.toString().length());

            }

        }
    });