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Unity Engine

Callback from native code

Understand how to use native-to-managed callback functionality.
Read time 1 minuteLast updated 20 days ago
Unity iOS supports limited native-to-managed callback functionality using one of the following methods:

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:
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