如何从.Net核心应用程序中调用AppKit方法？

Question

在Mac OS上运行.Net Core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。

按照documentation的PInvoke支持在MacOS，它是不明确的人会如何使用该命令与框架，例如AppKit的互动。

Answer 1

PInvoke仅适用于C方法，但由于Objective C运行时基于C方法，因此我们可以使用它们。 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，这个例子使用不安全的代码，因此需要在文件的csproj以下属性设置：

<AllowUnsafeBlocks>true</AllowUnsafeBlocks> 

下面是完整的代码，注意objc_msgSend需要进口多的时间与正确的签名。在C中，这将通过将其转换为具有正确签名的不同函数指针来完成。该框架还需要通过完整路径导入，因为CoreCLR没有针对框架的探测逻辑，所以它将搜索lib{sth}.dylib。

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 
     } 
    } 
}