# iOS UIActivity Sharing
## iOS UIActivity Sharing
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## UIActivity Sharing Simplified
From iOS 6 onwards, third-party applications have been enabled to **share data** such as text, URLs, or images using mechanisms like AirDrop, as outlined in Apple's [Inter-App Communication guide](https://developer.apple.com/library/archive/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/Inter-AppCommunication/Inter-AppCommunication.html#//apple_ref/doc/uid/TP40007072-CH6-SW3). This feature manifests through a system-wide *share activity sheet* that surfaces upon interacting with the "Share" button.
A comprehensive enumeration of all the built-in sharing options is available at [UIActivity.ActivityType](https://developer.apple.com/documentation/uikit/uiactivity/activitytype). Developers may opt to exclude specific sharing options if they deem them unsuitable for their application.
### **How to Share Data**
Attention should be directed towards:
* The nature of the data being shared.
* The inclusion of custom activities.
* The exclusion of certain activity types.
Sharing is facilitated through the instantiation of a `UIActivityViewController`, to which the items intended for sharing are passed. This is achieved by calling:
```bash
$ rabin2 -zq Telegram\ X.app/Telegram\ X | grep -i activityItems
0x1000df034 45 44 initWithActivityItems:applicationActivities:
```
Developers should scrutinize the `UIActivityViewController` for the activities and custom activities it's initialized with, as well as any specified `excludedActivityTypes`.
### **How to Receive Data**
The following aspects are crucial when receiving data:
* The declaration of **custom document types**.
* The specification of **document types the app can open**.
* The verification of the **integrity of the received data**.
Without access to the source code, one can still inspect the `Info.plist` for keys like `UTExportedTypeDeclarations`, `UTImportedTypeDeclarations`, and `CFBundleDocumentTypes` to understand the types of documents an app can handle and declare.
A succinct guide on these keys is available on [Stackoverflow](https://stackoverflow.com/questions/21937978/what-are-utimportedtypedeclarations-and-utexportedtypedeclarations-used-for-on-i), highlighting the importance of defining and importing UTIs for system-wide recognition and associating document types with your app for integration in the "Open With" dialogue.
### Dynamic Testing Approach
To test **sending activities**, one could:
* Hook into the `init(activityItems:applicationActivities:)` method to capture the items and activities being shared.
* Identify excluded activities by intercepting the `excludedActivityTypes` property.
For **receiving items**, it involves:
* Sharing a file with the app from another source (e.g., AirDrop, email) that prompts the "Open with..." dialogue.
* Hooking `application:openURL:options:` among other methods identified during static analysis to observe the app's response.
* Employing malformed files or fuzzing techniques to evaluate the app's robustness.
### References
*
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