如何从 NSNumber 转换为 .NET Object

Question

When working with .NET iOS targets (ie. net6.0-ios , net6.0-maccatalyst , Xamarin, MAUI, etc.), there are methods on NSNumber for converting to a specific .NET type. For example, .BooleanValue , .Int32Value , .DoubleValue , etc.

But what should one do if you don't know the type in advance, and just want a .NET object (boxing the actual bool , int , double , or whatever)?

Answer 1

Here's an extension method that I came up with. It uses the ObjCType encoded values , and handles bool values properly.

It's not perfect though. For example, NSNumber.FromByte(255).ToObject() gives back an object containing an Int16 , so it would appear that while "c" comes through for sbyte values, that byte value give "s" rather than "C" . Not sure why.

public static object ToObject(this NSNumber n)
{
    // This gets pretty close, but has some edges to be aware of:
    //   - byte returns short
    //   - ushort return int
    //   - uint returns long
    //   - ulong returns long unless it's > long.MaxValue
    //   - n/nu types return more primitive types (ex. nfloat => double)

    // https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtTypeEncodings.html

    switch (n.ObjCType)
    {
        // bool ("B" if originated from C99 or C++, but "c" with different class name if from ObjC)
        case "c" when n.Class.Name == "__NSCFBoolean":
        case "B":
            return n.BoolValue;

        // signed char
        case "c":
            return n.SByteValue;

        // signed int
        case "i":
            return n.Int32Value;

        // signed short
        case "s":
            return n.Int16Value;

        // signed long (32 bit)
        case "l":
            return n.Int32Value;

        // signed long long (64 bit)
        case "q":
            return n.Int64Value;

        // unsigned char
        case "C":
            return n.ByteValue;

        // unsigned int
        case "I":
            return n.UInt32Value;

        // unsigned short
        case "S":
            return n.UInt16Value;

        // unsigned long (32 bit)
        case "L":
            return n.UInt32Value;

        // unsigned long long (64 bit)
        case "Q":
            return n.UInt64Value;

        // float
        case "f":
            return n.FloatValue;

        // double
        case "d":
            return n.DoubleValue;
    }

    throw new ArgumentOutOfRangeException(nameof(n), n, $"Unknown ObjCType \"{n.ObjCType}\" (Class: \"{n.Class.Name}\")");
}