Refocus input based on nav index instead of willFocus event

The willFocus event by the navigator doesn't work properly (it doesn't
fire when screen has been navigated to) so use the nav index from state
instead to refocus the text input.

src/screens/CreatePineAddressScreen.js

@@ -78,7 +78,8 @@ const styles = StyleSheet.create({
   defaultPineAddressHostname: state.settings.defaultPineAddressHostname,
   pineAddressHostname: state.settings.pineAddressHostname,
   bitcoinNetwork: state.settings.bitcoin.network,
-  hasCreatedBackup: state.settings.user.hasCreatedBackup
+  hasCreatedBackup: state.settings.user.hasCreatedBackup,
+  navIndex: state.nav.index
 }))
 class CreatePineAddressScreen extends Component {
   static navigationOptions = ({ navigation }) => {
@@ -106,20 +107,16 @@ class CreatePineAddressScreen extends Component {
   componentDidMount() {
     const { navigation } = this.props;
 
-    this._willFocusListener = navigation.addListener('willFocus', this.componentWillFocus.bind(this));
-
     navigation.setParams({ canSubmit: false });
     navigation.setParams({ submit: this._onSubmit.bind(this) });
     navigation.setParams({ cancel: this._cancel.bind(this) });
   }
 
-  componentWillUnmount() {
-    this._willFocusListener.remove();
-  }
-
-  componentWillFocus() {
-    if (this._input) {
-      setTimeout(() => this._input.focus(), 300);
+  componentDidUpdate(prevProps) {
+    if (this.props.navIndex === 0 && prevProps.navIndex > 0) {
+      if (this._input && !this._input.isFocused()) {
+        setTimeout(() => this._input.focus(), 300);
+      }
     }
   }
 
@@ -272,6 +269,7 @@ class CreatePineAddressScreen extends Component {
 CreatePineAddressScreen.propTypes = {
   dispatch: PropTypes.func,
   navigation: PropTypes.any,
+  navIndex: PropTypes.number,
   keys: PropTypes.object,
   defaultPineAddressHostname: PropTypes.string,
   pineAddressHostname: PropTypes.string,