Different left button on different screens

I want to have burger button for drawer opening when there is only one route in stack. When we pushed a route to navigator I want to display back button. I wrote this code to handle this logic:

```
@autobind
renderLeftButton(routes) {
if (routes.length === 1) {
return (



);
}

return (

);
}

render() {
const currentRoutes = this.props.navigator.getCurrentRoutes();
const currentRoute = currentRoutes[currentRoutes.length - 1];
const tintColor = '#ffffff';
const {
props:{
title = currentRoute.title,
}
} = this;

let leftButtonConfig = {
tintColor,
title: this.renderLeftButton(currentRoutes),
};

const titleConfig = {
tintColor,
title,
};

if (currentRoutes.length === 1) {
leftButtonConfig.handler = this.props.openDrawer;
} else {
leftButtonConfig.handler = this.props.navigator.pop;
}

return (

)
}
```

The problem is no component updates on navigator.pop action. So the appearance of buttons don't change. Does anybody know the right solution to get this work?

Start by examining the NavigationBarOrig component and the navigator.pop action described in the issue, then trace how the current routes reach renderLeftButton. Reproduce the route-stack transition and verify that the left button changes between the drawer and back states after navigation.

Written by the indexing model from the issue text.