# Callback from native code

> Understand how to use native-to-managed callback functionality.

Unity iOS supports limited native-to-managed callback functionality using one of the following methods:

* [`UnitySendMessage`](#unitySendMessage)
* [Delegates](#delegates)

## Use UnitySendMessage

`UnitySendMessage` looks like this:

`UnitySendMessage("GameObjectName1", "MethodName1", "Message to send");`

There are three parameters:

* The name of the target GameObject
* The script method to call on that object
* The message string to pass to the called method

`UnitySendMessage` has the following limitations:

1. From native code, you can only call script methods that correspond to the following signature: `void MethodName(string message);`.
2. Calls to `UnitySendMessage` are asynchronous and have a delay of one frame.
3. If two or more GameObjects have the same name, this can cause conflicts when you use `UnitySendMessage`.

## Use delegates

When you use delegates, the method on the C# side must be static and marked with the `MonoPInvokeCallback` attribute.

To use delegates:

1. Pass the method as a delegate to the extern method.
2. Implement the extern method in native code as a function that accepts a pointer to functions with the corresponding signature.

The function pointer in the native code then points back to the static method in C#.

The C# code for this method looks like this:

```lang-cs
delegate void MyFuncType();

[AOT.MonoPInvokeCallback(typeof(MyFuncType))]

static void MyFunction() { }

[DllImport ("__Internal")] 

static extern void RegisterCallback(MyFuncType func);
```

The C code that accepts the callback then looks like this:

```lang-c
typedef void (*MyFuncType)();

void RegisterCallback(MyFuncType func) {}
```

> **Note:**
>
> Ensure string values returned from a native method are UTF--8 encoded and allocated on the heap.

## Additional resources

* [Automated plug-in integration for iOS](/engine/6000.3/manual/platform-specific/iphone/ios-developing/plugins-for-ios/ios-native-plugin-use/automated-integration.md)