Live character count for EditText

Could you review it and said if it's written good and/or is better way to do that?

My algorithm is:

Input roomNumber
If length of roomNumber is 8 set goToRoom state Enabled and color 0xFFFFFFFF
Else set goToRoom state Disabled and color 0xBBFFFFFF


Code of that algorithm is:

public class Join_room_screen extends Activity {

EditText numberRoom;
Button goToRoom;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

setContentView(R.layout.joinroom);

numberRoom = (EditText) findViewById(R.id.roomNumber);
goToRoom = (Button) findViewById(R.id.goToRoom);

TextWatcher watcher = new LocalTextWatcher();
goToRoom.addTextChangedListener(watcher);
updateButtonState();
}

void updateButtonState() {
boolean enabled = checkEditText(numberRoom);
if (enabled) {
goToRoom.setBackgroundColor(0xFFFFFFFF);
goToRoom.setEnabled(enabled);
} else {
goToRoom.setBackgroundColor(0xBBFFFFFF);
goToRoom.setEnabled(false);
}
}

private boolean checkEditText(EditText edit) {
return ((edit.getText().toString()).length() == 8 );
}

private class LocalTextWatcher implements TextWatcher {
public void afterTextChanged(Editable s) {
updateButtonState();
}

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

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


Here is my list of improvements:

-
Encapsulate all the logic in a custom textwatcher. This gives you the benefit to make the EnableViewTextWatcher reusable in other parts of your project (if you extract it from the Activity).

-
Programming against TextView vs EditText and View vs Button will make the code more flexible.

-
Limit visibility by using private keyword (class members, parameters and local variables)

-
Make class members, params and local variables final is possible

-
Follow the general Android coding guidelines regarding naming.

-
Use meaningful names when naming class, class members, params, and local variables

-
Use annotations in your code to improve code quality

-
Use constants instead of Magic Numbers.

public class RoomSelectActivity extends Activity {

    @Override
    protected void onCreate(@Nullable final Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_select_room);

        final TextView roomNumberText = (TextView) findViewById(R.id.tv_room_number);
        final View enabledView = findViewById(R.id.btn_go_to_room);

        final TextWatcher watcher = new EnableViewTextWatcher(roomNumberText, enabledView);
        roomNumberText.addTextChangedListener(watcher);
    }

    private static class EnableViewTextWatcher implements TextWatcher {

        private static final int LENGTH_TO_ENABLE_VIEW = 8;
        private static final int ENABLED_TEXT_COLOR  = 0xFFFFFFFF;
        private static final int DISABLED_TEXT_COLOR = 0xBBFFFFFF;

        private final TextView mWatchedTextView;
        private final View     mEnableView;

        public EnableViewTextWatcher(@NonNull final TextView textViewToWatch, @NonNull final View viewToEnable) {
            mWatchedTextView = textViewToWatch;
            mEnableView = viewToEnable;
            updateEnabledViewState();
        }

        public void afterTextChanged(@NonNull final Editable s) {
            updateEnabledViewState();
        }

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

        public void onTextChanged(@NonNull final CharSequence s, final int start, final int before, final int count) {
        }

        private boolean checkTextView(@NonNull final TextView textView) {
            return ((textView.getText().toString()).length() == LENGTH_TO_ENABLE_VIEW);
        }

        private void updateEnabledViewState() {
            final boolean enabled = checkTextView(mWatchedTextView);
            mEnableView.setBackgroundColor(enabled ? ENABLED_TEXT_COLOR : DISABLED_TEXT_COLOR);
            mEnableView.setEnabled(enabled);
        }
    }
}

StackExchange Code Review Q#74930, answer score: 9