Xamarin iOS绑定中如何处理(const void*)类型参数？

Got it, let's work through how to correctly bind that Objective-C method with const void* parameters in Xamarin.iOS.

First, your initial approach using IntPtr is on the right track—const void* in Objective-C maps naturally to IntPtr in C# since both represent generic unmanaged pointers. Here's the complete, correct binding code:

[Export("sendBytes:length:answer:length:")]
unsafe bool SendBytes(IntPtr data, nuint dataLength, IntPtr answer, nuint answerLength);

How to Use This Binding in C# #

The exact usage depends on whether the pointers are for input (you pass data to the native method) or output (the native method writes data to the pointer):

1. Passing Input Data (e.g., the data parameter)

If you have a C# byte[] you need to send to the native method, you can use a fixed block to get a pointer to the array's memory, then cast it to IntPtr:

byte[] sendData = new byte[] { 0x01, 0x02, 0x03 };
fixed (byte* dataPtr = sendData)
{
    bool success = YourNativeInstance.SendBytes((IntPtr)dataPtr, (nuint)sendData.Length, answerPtr, answerLength);
}

2. Handling Output Data (e.g., the answer parameter)

If the native method writes results to the answer pointer, you'll need to pre-allocate a C# buffer, get its pointer, and then copy the native-written data back:

// Assume you know the required buffer length from the native docs or other methods
nuint expectedAnswerLength = 16;
byte[] answerBuffer = new byte[expectedAnswerLength];

fixed (byte* answerPtr = answerBuffer)
{
    bool success = YourNativeInstance.SendBytes(dataPtr, dataLength, (IntPtr)answerPtr, expectedAnswerLength);
    if (success)
    {
        // answerBuffer now contains the data written by the native method
        // Use it as needed
    }
}

Important Memory Management Note #

If the native method retains the pointer beyond the method call (uncommon for most sendBytes-style methods, but worth checking), you'll need to pin the C# array to prevent the garbage collector from moving it. Use GCHandle for this:

byte[] sendData = new byte[100];
GCHandle pinnedHandle = GCHandle.Alloc(sendData, GCHandleType.Pinned);
try
{
    IntPtr dataPtr = pinnedHandle.AddrOfPinnedObject();
    bool success = YourNativeInstance.SendBytes(dataPtr, (nuint)sendData.Length, ...);
}
finally
{
    pinnedHandle.Free(); // Always free the handle to avoid memory leaks
}

That's all you need! This binding will correctly bridge the const void* parameters between Objective-C and C#.

内容的提问来源于stack exchange，提问作者drewfrisk