How do you get DllImportAttribute using System.Reflection?-CodePudding

How do you get info about a DllImport attribute?

I'm using monodevelop inspector to inspect a c# dll that wraps native dll

using System.Runtime.InteropServices;
namespace MonoMac.foo
{
 public class fooFramework
 {
  [DllImport ("/System/Library/Frameworks/foo")]
  public static extern void NSfoo ();
 }
}

I try to "replicate" the inspector functionality in my code using System.Reflection. I got no problem to get a MethodInfo on the NSfoo method. How do you get those (noncustom) attributes? I think

mymethodInfo.Attributes & MethodAttributes.PinvokeImpl

will tell me if the method consists in a extern call. But how can I get more information such as the path to the native dll?

EDIT:
I was using Attribute.GetCustomAttributes(mymethodInfo) or mymethodInfo.GetCustomAttributes(). For some reason, the returned list does not contain any attribute of type DllImport.

Asking explicitly for a DllImportAttribute is the way to go : var dllImport =(DllImportAttribute)mymethodInfo.GetCustomAttribute(typeof(DllImportAttribute)).
If attribute is not null, the "path" is in the property named Value.

CodePudding user response：

Since extern is always static you need to find all static methods and filter them by result of GetCustomAttribute() method:

public class fooFramework
{
    [DllImport ("/System/Library/Frameworks/foo")]
    public static extern void NSfoo ();
}
...
public class MethodData
{
    public MethodInfo MethodInfo { get; set; }

    public DllImportAttribute Attribute { get; set; }

    public string DllPath => Attribute.Value;
}
...
public static List<MethodData> GetDllImportMethods(Type classType)
{
    var methods = classType.GetMethods(BindingFlags.Public | BindingFlags.Static);
    var result = new List<MethodData>();
    foreach (var methodInfo in methods)
    {
        var dllImportAttribute =
            methodInfo.GetCustomAttribute(typeof(DllImportAttribute));
        if (dllImportAttribute == null)
            continue;
        result.Add(new MethodData()
        {
            MethodInfo = methodInfo,
            Attribute = (DllImportAttribute)dllImportAttribute
        });
    }

    return result;
}
...
//Usage:
var methods = GetDllImportMethods(typeof(fooFramework));
Console.WriteLine(methods[0].DllPath); // /System/Library/Frameworks/foo