Feature/toggle (#2492)

* add toggle functionality

* add documentation

docs/api/navigators/DrawerNavigator.md

@@ -68,6 +68,12 @@ To open and close drawer, navigate to `'DrawerOpen'` and `'DrawerClose'` respect
 this.props.navigation.navigate('DrawerOpen'); // open drawer
 this.props.navigation.navigate('DrawerClose'); // close drawer
 ```
+If you would like to toggle the drawer you can navigate to `'DrawerToggle'`, and this will choose which navigation is appropriate for you given the drawers current state.
+
+```js
+// fires 'DrawerOpen'/'DrawerClose' accordingly
+this.props.navigation.navigate('DrawerToggle');
+```
 
 ## API Definition
 
@@ -181,7 +187,7 @@ The navigator component created by `DrawerNavigator(...)` takes the following pr
    screenProps={/* this prop will get passed to the screen components and nav options as props.screenProps */}
  />
  ```
- 
+
  ### Nesting `DrawerNavigation`
- 
+
 Please bear in mind that if you nest the DrawerNavigation, the drawer will show below the parent navigation.

src/navigators/DrawerNavigator.js

@@ -63,6 +63,9 @@ const DrawerNavigator = (
       DrawerOpen: {
         screen: () => null,
       },
+      DrawerToggle: {
+        screen: () => null,
+      },
     },
     {
       initialRouteName: 'DrawerClose',

src/views/Drawer/DrawerView.js

@@ -63,6 +63,12 @@ export default class DrawerView<T: *> extends PureComponent<void, Props, void> {
       const { routes, index } = nextProps.navigation.state;
       if (routes[index].routeName === 'DrawerOpen') {
         this._drawer.openDrawer();
+      } else if (routes[index].routeName === 'DrawerToggle') {
+        if (this._drawer.state.drawerShown) {
+          this.props.navigation.navigate('DrawerClose');
+        } else {
+          this.props.navigation.navigate('DrawerOpen');
+        }
       } else {
         this._drawer.closeDrawer();
       }