Question

I need to detect text changes in an EditText. I’ve tried TextWatcher, but it doesn’t work in a way I would expect it to. Take the onTextChanged method:

public void onTextChanged( CharSequence s, int start, int before, int count )

Say I have the text “John” in already in the EditText. If press another key, “e”, s will be “Johne”, start will be 0, before will be 4, and count will be 5. The way I would expect this method to work would be the difference between what the EditText previously was, and what it’s about to become.

So I would expect:

s = "Johne"
start = 4 // inserting character at index = 4
before = 0 // adding a character, so there was nothing there before
count = 1 // inserting one character

I need to be able to detect individual changes every time a key is pressed. So if I have text “John”, I need to know “e” was added at index 4. If I backspace “e”, I need to know “e” was removed from index 4. If I put the cursor after “J” and backspace, I need to know “J” was removed from index 0. If I put a “G” where “J” was, I want to know “G” replaced “J” at index 0.

How can I achieve this? I can’t think of a reliable way to do this.

Answer 1

Use a textwatcher and do the diff yourself. store the previous text inside the watcher, and then compare the previous text to whatever sequence you get onTextChanged. Since onTextChanged is fired after every character, you know your previous text and the given text will differ by at most one letter, which should make it simple to figure out what letter was added or removed where. ie:

new TextWatcher(){ 
    String previousText = theEditText.getText();

    @Override 
    onTextChanged(CharSequence s, int start, int before, int count){
        compare(s, previousText); //compare and do whatever you need to do
        previousText = s;
    }

    ...
}