expo-core

JavaScript installation

$ yarn add expo-core

# or

$ npm install expo-core --save

Installation

iOS (Cocoapods)

If you're using Cocoapods, add the following dependency to your Podfile:

pod 'EXCore', path: '../node_modules/expo-core/ios'

and run pod install.

Android

1. Append the following lines to android/settings.gradle:

   include ':expo-core'
   project(':expo-core').projectDir = new File(rootProject.projectDir, '../node_modules/expo-core/android')

2. Insert the following lines inside the dependencies block in android/app/build.gradle:

   compile project(':expo-core')

3. If you're using ProGuard, you'll need to append these lines to your ProGuard rules file for it not to strip out methods required for Expo modules to work.

   -keepclassmembers class * {
     @expo.core.interfaces.ExpoProp *;
   }
   -keepclassmembers class * {
     @expo.core.interfaces.ExpoMethod *;
   }

Usage

Glossary

• Native code — iOS/Android native code.

• Client code — code over the bridge, for React Native it would be the JavaScript app, for Flutter it would be Flutter code.

• Internal module — a class implementing EXInternalModule/expo.core.interfaces.InternalModule interface. Its instance can be exposed internally to other modules via Module Registry (how dependants reference modules differs between platforms).

• Module interface — an interface that should be implemented by the dependency so it can act as an implementation of it.

  On Android modules implement an external interface (expo-file-system package implements interface provided by expo-file-system-interface). Dependants may access the implementations by calling

  public <T> T getModule(Class<T> interfaceClass);

  method on the module registry.

  On iOS its the consumer who defines required protocol. Implementations are identified by a protocol. Dependants access the implementation by calling

  - (id)getModuleImplementingProtocol:(Protocol *)protocol;

  method on the module registry.

• Module Registry — well, a registry of modules. Instance of this class is used to fetch another internal or exported module.

• Exported methods — a subset of instance methods of a given module that should get exposed to client code by specific platform adapter.

• Exported module — a subclass of {EX,expo.core.}ExportedModule. Its methods annotated with expo.core.ExpoMethod/EX_EXPORT_METHOD_AS are exported to client code.

• View manager — a class capable of providing platform adapter with custom views.

Registering modules in the registry

iOS

1. Open the header file for your module.
2. Import <EXCore/EXInternalModule.h>.
3. Add EXModule to a list of implemented interfaces by the module instances (eg. NSObject <EXInternalModule>).
4. Open the implementation file for your module and implement methods required by the protocol.
5. Use EX_REGISTER_MODULE(); macro to register the module.
6. That's it!

Android

1. Add expo.core.interfaces.InternalModule to your class's imports.
2. Make your module class implement InternalModule interface.
   1. Implement public List<Class> getExportedInterfaces();. Return a list of module interfaces implemented by the class, for example:

      return Collections.singletonList((Class) expo.interfaces.filesystem.FileSystem.class);

3. Create a Package class for your module, unless you already have one.
   1. A Package class should implement expo.core.Package interface (a BasePackage class is provided for you not to have to implement all the initialization flavors at once).
   2. Add the Package to a List provided to ModuleRegistryBuilder.

      new ModuleRegistryBuilder(
        Arrays.<Package>asList(
          new FileSystemPackage()
        )
      )

4. Add your module to be returned by List<InternalModule> createInternalModules(Context context);.
5. You're good to go!

Exporting module to client code

iOS

When registering your module for export to client code, you must first decide whether the class will only be exported to client code or will it be both internal and exported module. If the former is applicable, you easily just subclass EXExportedModule and use macro EX_EXPORT_MODULE(clientCodeName) to provide a name under which it should be exported. If your module should be both internal and exported module, you also have to subclass EXExportedModule, but this time use EX_REGISTER_MODULE() in the implementation and then manually override methods exportedInterfaces and exportedModuleName.

Android

Subclass expo.core.ExportedModule and add your module to a list returned by Package in createExportedModules().

Exporting methods and calling exported methods

iOS

Use EX_EXPORT_METHOD_AS(exportedName, definition) macro to export given method to client code. Note that for the module to be available in the client code you have to provide a non-empty client code name in EX_EXPORT_MODULE(clientCodeName) or - (const NSString *)exportedModuleName. For now, arguments have to use basic, object types, like NSString *, NSDictionary *, NSNumber *. Methods are required to receive EXPromiseResolveBlock and EXPromiseRejectBlock as two last arguments.

Android

Given that your module subclasses expo.core.ExportedModule and it is returned by the respective Package, you just have to annotate the given method with @ExpoMethod annotation. Methods are required to receive expo.core.Promise as the last argument.

Exporting constants to client code

iOS

Implement - (NSDictionary *)constantsToExport method to export constants to client code.

Android

Override public Map<String, Object> getConstants(); method to export constants to client code.

Creating a custom view manager

iOS

Subclass EXViewManager and override at least - (UIView *)view and - (NSString *)viewName. Register it with EX_REGISTER_MODULE().

Use EX_VIEW_PROPERTY(propName, propClass, viewClass) to define custom view properties.

Android

TODO: ViewManager from interface to a class

Implement expo.core.interfaces.ViewManager in your class and respond with its instance in List<ViewManager> createViewManagers(Context context); in corresponding Package.

Annotate prop setter methods with @ExpoProp(name = <name>) to define custom view properties.