Android EditText combined with InputFilter vs TextWatcher

Question

Basically I would like to know more in depth difference and usage scenario for InputFilter and TextWatcher.

As per the docs:
InputFilter: InputFilters can be attached to Editables to constrain the changes that can be made to them.

TextWatcher: When an object of a type is attached to an Editable, its methods will be called when the text is changed. So it can be used to constrain the change correct me if I am wrong

Which one is better? and why? My scenario is I need an EditText with minimum 6 characters after decimal point in it.

Answer 1

TextWatcher is used to be notified whenever user types.
InputFilter decides what can be typed.

For example,
Suppose I want to allow the user to enter temperature. This temperature has to be all numbers and can only contain two digits after decimal. If you look closely, I need both TextWatcher and InputFilter.

InputFilter would allow only numbers.

final InputFilter[] filters = new InputFilter[]
                { DigitsKeyListener.getInstance(true, true) };
textView.setFilters(filters);   

Now, this would allow numbers with more than two digits after decimal. Why? Because InputFilter only restricts what keys can be typed. Here's when TextWatcher comes in.

@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
    // you need this to avoid loops
    // or your stack will overflow
    if(!textView.hasWindowFocus() || textView.hasFocus() || s == null){
        return;
    }
    // Now you can do some regex magic here to see 
    // if the user has entered a valid string
    // "\\d+.\\d{6,}" for your case

}