title: Error: Element type is invalid React Native
body: <p>When I launch my app on android I get that error: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it's defined in, or you might have mixed up default and named imports.</p>
  <p>Here is my Navigation.js</p>
  <pre><code>import React from 'react'
  import { createStackNavigator } from 'react-navigation-stack'
  import { Dimensions } from 'react-native'
  import {createAppContainer, } from 'react-navigation';
  import { createBottomTabNavigator } from 'react-navigation-tabs'
  
  import Home from '../screens/Home'
  import AddCollege from '../screens/AddCollege'
  import ViewCollege from '../screens/ViewCollege'
  import ViewSchool from '../screens/ViewSchool'
  import AddSchool from '../screens/AddSchool'
  import Profile from '../screens/Profile'
  import Dashboard from '../screens/Dashboard'
  import Settings from '../screens/Settings'
  import ManageProfile from '../screens/ManageProfile'
  
  import { Ionicons } from &quot;react-native-vector-icons&quot;;
  
  const HEIGHT = Dimensions.get('window').height
  const WIDTH = Dimensions.get('window').width
  
  const HomeStack = createStackNavigator(
      {
        Home: Home,
        AddCollege: AddCollege,
        ViewCollege: ViewCollege,
        ViewSchool: ViewSchool,
        AddSchool: AddSchool,
        ManageProfile: ManageProfile
      },
      {
        defaultNavigationOptions: {
           headerStyle: {
            backgroundColor: 'black',
            height: HEIGHT / 9
          },
          headerTintColor: '#fff',
        },
      }
      );
  
      const ProfileStack = createStackNavigator(
        {
          Profile: Profile,
         
        },
        {
          defaultNavigationOptions: {
            headerTitleStyle: {
              textAlign: 'center',
            },
             headerStyle: {
              backgroundColor: 'black',
              height: HEIGHT / 9
              //marginTop: 24 ,
            },
            
            headerTintColor: '#fff',
            title: 'Profile', 
           
          },
        }
      );
  
      const DashboardStack = createStackNavigator(
        {
          Dashboard: Dashboard,   
        },
        {
          defaultNavigationOptions: {
            title: 'Dashboard',
            headerStyle: {
              backgroundColor: 'black',
              height: HEIGHT / 9
            },
            headerTintColor: '#fff',
           
          },
        }
      );
  
      const SettingsStack = createStackNavigator(
        {
          Settings: Settings,
        },
        {
          defaultNavigationOptions: {
          title: 'Settings ',
            headerStyle: {
              backgroundColor: 'black',
              height:HEIGHT / 9
            },
            headerTitleStyle: {
                  color: '#fff',
              },    
          },
        },
      );
  
  
  const MainApp = createBottomTabNavigator({
      Home: {
        screen: HomeStack ,
        navigationOptions: {
              tabBarLabel: 'Home', 
              tabBarIcon: ({ tintColor }) =&gt; (
                  &lt;Ionicons name=&quot;md-home&quot; color={tintColor} size={30} /&gt;
              )
            }
          }, 
      Profile: {
        screen: ProfileStack,
        navigationOptions: {
              tabBarLabel: 'Profile', 
              tabBarIcon: ({ tintColor }) =&gt; (
                  &lt;Ionicons name=&quot;md-user&quot; color={tintColor} size={30} /&gt;
              )
            }
          }, 
      Dashboard: { 
        screen: DashboardStack,
         navigationOptions: {
              tabBarLabel: 'Dashboard', 
              tabBarIcon: ({ tintColor }) =&gt; (
                  &lt;Ionicons name=&quot;md-clipboard&quot; color={tintColor} size={30} /&gt;
              )
            }
          } ,
      Settings: {
        screen : SettingsStack ,
         navigationOptions: {
              tabBarLabel: 'Settings', 
              tabBarIcon: ({ tintColor }) =&gt; (
                  &lt;Ionicons name=&quot;md-settings&quot; color={tintColor} size={30} /&gt;
              )
          }
        }
    },
    {
      tabBarOptions: {
        labelStyle: {
       fontSize: 12,
       padding: 0,
        margin: 0
    },
          activeTintColor: 'red', 
          inactiveTintColor: 'white',
          style:{height: HEIGHT / 10,  backgroundColor: 'black' },
          showIcon: true,
          padding: 0,
          margin: 0
      }
    });
  
    export default createAppContainer(MainApp);
  </code></pre>