> 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-flutter-addapi1.md).

# guide/gs/flutter/addAPI1

***

#### Introduction

The Flutter API for Apryse Mobile SDK includes all of the most used functions and methods for viewing, annotating and saving PDF documents. However, it is possible your app may need access to APIs that are available as part of the native API, but are not directly available to Flutter.

There are 2 different ways to use Apryse Flutter API on iOS or Android:

* Present a document via a plugin.
* Show an Apryse document view via a Widget.

This guide will demonstrate how to add a new functionality to both approaches.

The examples provided will show you how to add the following to the Flutter interface:

* `readOnly` viewer configuration option that determines if the viewer will allow edits to the document.
* `getPageCropBox` function that returns a `PTRect` object containing information about the crop box of a specified page.
* `startZoomChangedListener` event listener that is raised when the zoom ratio is changed in the current document.

You can follow the same pattern to add new functions and viewer configuration options that your Flutter app may need. These additions could be simple ones, which expose one piece of functionality, or custom ones, that expose a series of native commands under the hood.

Prior to following this guide, we highly recommend you to go through the official guide here: [Writing Platform-specific code](https://flutter.dev/docs/development/platform-integration/platform-channels?tab=android-channel-java-tab) to have a better understanding of the system.

#### 1. Fork and clone Apryse's Flutter Repo

The source is hosted on GitHub here: [https://github.com/ApryseSDK/pdftron-flutter](https://github.com/ApryseSDK/pdftron-flutter/)

Fork the project and clone a copy of the repository to your disk.

### Adding the `readOnly` viewer configuration option

#### 2. Define the new viewer configuration option in Dart

The `config.dart` file is responsible for setting all of the viewer configuration options.

```dart
var _readOnly;

set readOnly(bool value) => _readOnly = value;

Config.fromJson(Map<String, dynamic> json) :
    _readOnly = json['readOnly'];

Map<String, dynamic> toJson() => {
    'readOnly': _readOnly,
};
```


---

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