Writing native modules
If we cannot find an open source module to meet our application's needs, we may need to write our own. For instance, we might need to write our own native module if we require some very specific behavior or if we have code from previously developed native applications that we want to incorporate into a React Native project.
We are going to create native modules-one for iOS and one for Android-that allow the user to select an image from their device's media library when the avatar icon is pressed on the profile page. As we develop these modules, we'll look at exposing both native methods and constants. We will also look at several different methods of communicating between JavaScript and native code, including callbacks, promises, and events.
Native modules in iOS
As we mentioned at the beginning of this chapter, in order to follow along in this section, you will need some basic Objective-C knowledge. When writing native modules for iOS, we will also work...
