Add lazy requiring screens components (#115)

* Add lazy requiring screens components

* Fix naming

src/screens.native.js

@@ -17,7 +17,7 @@ const getViewManagerConfigCompat = name =>
     ? UIManager.getViewManagerConfig(name)
     : UIManager[name];
 
-export function useScreens(shouldUseScreens = true) {
+function useScreens(shouldUseScreens = true) {
   USE_SCREENS = shouldUseScreens;
   if (USE_SCREENS && !getViewManagerConfigCompat('RNSScreen')) {
     console.error(
@@ -26,20 +26,33 @@ export function useScreens(shouldUseScreens = true) {
   }
 }
 
-export function screensEnabled() {
+function screensEnabled() {
   return USE_SCREENS;
 }
 
-export const NativeScreen = requireNativeComponent('RNSScreen', null);
+let NativeScreenValue;
+let NativeScreenContainerValue;
 
-const AnimatedNativeScreen = Animated.createAnimatedComponent(NativeScreen);
+const ScreensNativeModules = {
+  get NativeScreen() {
+    NativeScreenValue =
+      NativeScreenValue || requireNativeComponent('RNSScreen', null);
+    return NativeScreenValue;
+  },
 
-export const NativeScreenContainer = requireNativeComponent(
-  'RNSScreenContainer',
-  null
+  get NativeScreenContainer() {
+    NativeScreenContainerValue =
+      NativeScreenContainerValue ||
+      requireNativeComponent('RNSScreenContainer', null);
+    return NativeScreenContainerValue;
+  },
+};
+
+const AnimatedNativeScreen = Animated.createAnimatedComponent(
+  ScreensNativeModules.NativeScreen
 );
 
-export class Screen extends React.Component {
+class Screen extends React.Component {
   setNativeProps(props) {
     this._ref.setNativeProps(props);
   }
@@ -77,12 +90,26 @@ export class Screen extends React.Component {
   }
 }
 
-export class ScreenContainer extends React.Component {
+class ScreenContainer extends React.Component {
   render() {
     if (!USE_SCREENS) {
       return <View {...this.props} />;
     } else {
-      return <NativeScreenContainer {...this.props} />;
+      return <ScreensNativeModules.NativeScreenContainer {...this.props} />;
     }
   }
 }
+
+module.exports = {
+  ScreenContainer,
+  Screen,
+  get NativeScreen() {
+    return ScreensNativeModules.NativeScreen;
+  },
+
+  get NativeScreenContainer() {
+    return ScreensNativeModules.NativeScreenContainer;
+  },
+  useScreens,
+  screensEnabled,
+};