Native Base Input Refs Not Being Set

So I'm working with the Native Base <Input> tag, trying to set refs to handle "tabbing" through form fields. I've got the following code: <Item floatingLabel> <Label style={{ color: "#fff" }}>First Name</Label> <Input ref={input => { this.firstNameRef = input; }} onSubmitEditing={() => { this.lastNameRef._root.focus(); }} returnKeyType={"next"} /> </Item> <Item floatingLabel last> <Label style={{