c# - 如何从 .Net Core 应用程序 PInvoke AppKit 方法？

Question

在 Mac OS 上的 .Net Core 上运行时，是否可以使用 PInvoke 调用 AppKit 方法？具体来说，我想使用 NSWorkspace.Recycle 方法。

根据documentation MacOS 支持 PInvoke，只是不清楚如何使用它与 AppKit 等框架进行交互。

Answer 1

PInvoke 仅适用于 C 方法，但由于 Objective C 运行时基于 C 方法，我们可以使用它们。 Xamarin 将提供所有必要的设置和便利方法，但这是可能的。请注意，此示例使用不安全代码，因此需要在 csproj 文件中设置以下属性:

<AllowUnsafeBlocks>true</AllowUnsafeBlocks>

下面是完整代码，注意 objc_msgSend需要使用正确的签名多次导入。在 C 中，这可以通过将其转换为具有正确签名的不同函数指针来完成。框架也需要通过完整路径导入，因为CoreCLR没有框架的探测逻辑，它会搜索 lib{sth}.dylib反而。

using System;
using System.IO;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading;

namespace NSWorkspaceExample
{
    public class Program
    {
        static void Main(string[] args)
        {
            var testFile = Path.Combine(Directory.GetCurrentDirectory(), "test.txt");
            File.WriteAllText(testFile, "example file content");

            var cfstrTestFile = CreateCFString(testFile);
            var nsURL = objc_getClass("NSURL");
            var fileUrl = objc_msgSend_retIntPtr_IntPtr(nsURL, GetSelector("fileURLWithPath:"), cfstrTestFile);
            CFRelease(cfstrTestFile);

            var urlArray = CreateCFArray(new IntPtr[] {fileUrl});

            var nsWorkspace = objc_getClass("NSWorkspace");
            var sharedWorkspace = objc_msgSend_retIntPtr(nsWorkspace, GetSelector("sharedWorkspace"));

            objc_msgSend_retVoid_IntPtr_IntPtr(sharedWorkspace, GetSelector("recycleURLs:completionHandler:"), urlArray, IntPtr.Zero);

            CFRelease(urlArray);
            CFRelease(fileUrl);
            CFRelease(sharedWorkspace);

            // sleep since we didn't go through the troubles of creating a block object as a callback
            Thread.Sleep(1000);
        }

        public static IntPtr GetSelector(string name)
        {
            IntPtr cfstrSelector = CreateCFString(name);
            IntPtr selector = NSSelectorFromString(cfstrSelector);
            CFRelease(cfstrSelector);
            return selector;
        }

        private const string FoundationFramework = "/System/Library/Frameworks/Foundation.framework/Foundation";
        private const string AppKitFramework = "/System/Library/Frameworks/AppKit.framework/AppKit";

        public unsafe static IntPtr CreateCFString(string aString)
        {
            var bytes = Encoding.Unicode.GetBytes(aString);
            fixed (byte* b = bytes) {
                var cfStr = CFStringCreateWithBytes(IntPtr.Zero, (IntPtr)b, bytes.Length, CFStringEncoding.UTF16, false);
                return cfStr;
            }
        }

        // warning: this doesn't call retain/release on the elements in the array
        public unsafe static IntPtr CreateCFArray(IntPtr[] objectes)
        {
            fixed(IntPtr* vals = objectes) {
                 return CFArrayCreate(IntPtr.Zero, (IntPtr)vals, objectes.Length, IntPtr.Zero);
            }
        }

        [DllImport(FoundationFramework)]
        public static extern IntPtr CFStringCreateWithBytes(IntPtr allocator, IntPtr buffer, long bufferLength, CFStringEncoding encoding, bool isExternalRepresentation);

        [DllImport(FoundationFramework)]
        public static extern IntPtr CFArrayCreate(IntPtr allocator, IntPtr values, long numValues, IntPtr callbackStruct);

        [DllImport(FoundationFramework)]
        public static extern void CFRetain(IntPtr handle);

        [DllImport(FoundationFramework)]
        public static extern void CFRelease(IntPtr handle);

        [DllImport(AppKitFramework, CharSet = CharSet.Ansi)]
        public static extern IntPtr objc_getClass(string name);

        [DllImport(AppKitFramework)]
        public static extern IntPtr NSSelectorFromString(IntPtr cfstr);

        [DllImport(FoundationFramework, EntryPoint="objc_msgSend")]
        public static extern IntPtr objc_msgSend_retIntPtr(IntPtr target, IntPtr selector);

        [DllImport(FoundationFramework, EntryPoint="objc_msgSend")]
        public static extern void objc_msgSend_retVoid_IntPtr_IntPtr(IntPtr target, IntPtr selector, IntPtr param1, IntPtr param2);

        [DllImport(FoundationFramework, EntryPoint="objc_msgSend")]
        public static extern IntPtr objc_msgSend_retIntPtr_IntPtr(IntPtr target, IntPtr selector, IntPtr param);

        [DllImport(FoundationFramework, EntryPoint="objc_msgSend")]
        public static extern void objc_msgSend_retVoid(IntPtr target, IntPtr selector);

        public enum CFStringEncoding : uint
        {
            UTF16 = 0x0100,
            UTF16BE = 0x10000100,
            UTF16LE = 0x14000100,
            ASCII = 0x0600
        }
    }
}