title: React Native Expo Image Saving Attempt: TypeError: Null is not an object
body: <p>I'm trying to get an image to save to my device. I am usint react-native-view-shot to capture a component and react-native-community/cameraroll to save it.</p>
  
  <p>I am getting an error:</p>
  
  <pre><code>[Unhandled promise rejection: TypeError: null is not an object (evaluating '_nativeInterface.default.saveToCameraRoll')]
  * http://172.16.17.76:19001/node_modules/expo/AppEntry.bundle?platform=ios&amp;dev=true&amp;minify=false&amp;hot=false:152104:40 in save
  * http://172.16.17.76:19001/node_modules/expo/AppEntry.bundle?platform=ios&amp;dev=true&amp;minify=false&amp;hot=false:150956:45 in &lt;unknown&gt;
  - node_modules/react-native-view-shot/src/index.js:231:31 in ViewShot#onCapture
  - node_modules/react-native-view-shot/src/index.js:214:9 in firstLayoutPromise.then.then$argument_0
  - node_modules/promise/setimmediate/core.js:37:14 in tryCallOne
  - node_modules/promise/setimmediate/core.js:123:25 in setImmediate$argument_0
  - node_modules/react-native/Libraries/Core/Timers/JSTimers.js:146:14 in _callTimer
  - node_modules/react-native/Libraries/Core/Timers/JSTimers.js:194:17 in _callImmediatesPass
  - node_modules/react-native/Libraries/Core/Timers/JSTimers.js:458:30 in callImmediates
  * [native code]:null in callImmediates
  - node_modules/react-native/Libraries/BatchedBridge/MessageQueue.js:407:6 in __callImmediates
  - node_modules/react-native/Libraries/BatchedBridge/MessageQueue.js:143:6 in __guard$argument_0
  - node_modules/react-native/Libraries/BatchedBridge/MessageQueue.js:384:10 in __guard
  - node_modules/react-native/Libraries/BatchedBridge/MessageQueue.js:142:17 in __guard$argument_0
  * [native code]:null in flushedQueue
  * [native code]:null in invokeCallbackAndReturnFlushedQueue
  </code></pre>
  
  <p>But according to the GitHub page, saveToCameraRoll is indeed a function (<a href="https://github.com/react-native-community/react-native-cameraroll" rel="nofollow noreferrer">https://github.com/react-native-community/react-native-cameraroll</a>). This is my code:</p>
  
  <pre><code>  import React, { Component } from 'react';
    import { ScrollView, StyleSheet} from 'react-native';
    import { ExpoLinksView } from '@expo/samples';
    import ViewShot from "react-native-view-shot";
    import CameraRoll from "@react-native-community/cameraroll";
  
    export default class LinksScreen extends Component {
        onCapture = uri =&gt; {
            console.log("do something with ", uri);
            CameraRoll.saveToCameraRoll(uri);
        }   
        render(){
      return (
        &lt;ScrollView style={styles.container}&gt;
            &lt;ViewShot onCapture={this.onCapture} captureMode="mount"&gt;
                &lt;ExpoLinksView /&gt;
            &lt;/ViewShot&gt;
        &lt;/ScrollView&gt;
      );  
  
     }
    }
  
    LinksScreen.navigationOptions = { 
      title: 'Links',
    };
  
    const styles = StyleSheet.create({
      container: {
        flex: 1,
        paddingTop: 15, 
        backgroundColor: '#fff',
      },  
    });
  </code></pre>
  
  <p>Thanks for the help!</p>