Callback from native code

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

• UnitySendMessage
• Delegates

Tip: Managed-to-unmanaged calls are processor-intensive on iOS. Try to avoid calling multiple native methods per frame.

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 GameObjectsThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
   See in Glossary 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:

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:

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