* Make StackNavigator keyboard aware
One thing that has always annoyed me in React Navigation is the handling of the keyboard. When a keyboard is visible on screen and a navigation action occurs (either by tapping a button or using a gesture), the keyboard tends to stay on screen until the transition completes. This feels janky and broken. On native iOS, for instance, the keyboard hides immediately when the navigation starts, and if the transition is cancelled (say, when the user releases the gesture), the keyboard reappears.
This PR introduces a "KeyboardAwareNavigator" higher order component that is enabled on the StackNavigator, unless a `disableKeyboardHandling` prop is passed into the StackNavigator's configuration.
* Set status bar in keyboard handling example
* Call gesture props in keyboard aware navigator if available
* Fix formatting
The navigation prop should also pass through, and be prioritized over context because it is more explicit
This also fixes an incorrect warning/invariant
Adds a new state persistence mechanisms to all of the navigators via createNavigationContainer
There are two new props that you can provide to a navigation container: `storageKey` and `renderLoading`.
`storageKey` is the string key to be used with AsyncStorage while saving and persisting navigation state. To disable persistence, set to null.
`renderLoading` allows you to render something while the navigator re-hydrates its state and loads its initial URL. By default this returns null, but Expo users will want to render a <AppLoading /> component for smooth app launches
There is also functionality in this PR to observe errors that come from re-hydrating state, and gracefully recover by dispatching an init action.
Also this revises the init action to *reset* the navigation state, rather than preserve the previous state.
