> For the complete documentation index, see [llms.txt](https://docs.apryse.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.apryse.com/reusable-content/guide/guide-gs-reactnative-addapi3.md).

# guide/gs/reactNative/addAPI3

The logic is to get the PDF view controller and if the field names are valid, use the controller to get the fields from the current document.

### Adding the `onLayoutChanged` event listener

#### 2. Define the new listener in TS

Event listeners are handled in `DocumentView.tsx`. Add the following to the file:

```js
static propTypes = {
    ...
    onLayoutChanged: func<() => void>(),
}

onChange = (event) => {
    if (event.nativeEvent.onLeadingNavButtonPressed) {
        ...
    } else if (event.nativeEvent.onLayoutChanged) {
      if (this.props.onLayoutChanged) {
        this.props.onLayoutChanged();
      }
    }
}
```

The `onLayoutChanged` event listener does not require any arguments. If your event listener requires arguments, access them using `event.nativeEvent.exampleArg`.

For event listeners and other props that accept functions, use the `func` helper method. This helper returns flexible types that allow custom checks for TypeScript users, while maintaining standard run-time checks for all users.

While you are adding types, consider representing objects with reusable object types. You can use existing ones, or create a new type alias or interface in `AnnotOptions.ts` (see [Object Types](https://www.typescriptlang.org/docs/handbook/2/objects.html)).


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.apryse.com/reusable-content/guide/guide-gs-reactnative-addapi3.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.