Xamarin iOS binding project

I have an Xamarin.iOS application, and I want to reference a binding project so that I can use a .a file in my project. But I get this error when I try to build:

linker command failed with exit code 1 (use -v to see invocation) /Users/darius/Mobile-MyApp/Source/MyApp/MyApp.Touch/MTOUCH: Error MT5216: Native linking failed for '/Users/darius/Mobile-MyApp/Source/MyApp/MyApp.Touch/obj/iPhone/Debug/device-builds/iphone7.1-11.0.3/mtouch-cache/arm64/libAcrCloudSdkIosBinding.dll.dylib'. Please file a bug report at http://bugzilla.xamarin.com (MT5216) (Touchshop.Touch)

I checked what architectures the .a file supports with this command line:

xcrun -sdk iphoneos lipo -info libACRCloud_IOS_SDK.a

and it outputs:

Architectures in the fat file: libACRCloud_IOS_SDK.a are: armv7 i386 x86_64 arm64

I put the .a in the NativeReferences folder.

Here is my ApiDefinition.cs:

using System;

using UIKit;
using Foundation;
using ObjCRuntime;
using CoreGraphics;

namespace AcrCloudSdkIos
{
// typedef void (^ACRCloudResultBlock)(NSString *, ACRCloudResultType);
delegate void ACRCloudResultBlock(string arg0, ACRCloudResultType arg1);

// typedef void (^ACRCloudResultWithFpBlock)(NSString *, NSData *);
delegate void ACRCloudResultWithFpBlock(string arg0, NSData arg1);

// typedef void (^ACRCloudStateBlock)(NSString *);
delegate void ACRCloudStateBlock(string arg0);

// typedef void (^ACRCloudVolumeBlock)(float);
delegate void ACRCloudVolumeBlock(float arg0);

// @interface ACRCloudConfig : NSObject
[BaseType(typeof(NSObject))]
interface ACRCloudConfig
{
    // @property (retain, nonatomic) NSString * accessKey;
    [Export("accessKey", ArgumentSemantic.Retain)]
    string AccessKey { get; set; }

    // @property (retain, nonatomic) NSString * accessSecret;
    [Export("accessSecret", ArgumentSemantic.Retain)]
    string AccessSecret { get; set; }

    // @property (retain, nonatomic) NSString * host;
    [Export("host", ArgumentSemantic.Retain)]
    string Host { get; set; }

    // @property (retain, nonatomic) NSString * audioType;
    [Export("audioType", ArgumentSemantic.Retain)]
    string AudioType { get; set; }

    // @property (retain, nonatomic) NSString * homedir;
    [Export("homedir", ArgumentSemantic.Retain)]
    string Homedir { get; set; }

    // @property (retain, nonatomic) NSString * uuid;
    [Export("uuid", ArgumentSemantic.Retain)]
    string Uuid { get; set; }

    // @property (retain, nonatomic) NSString * protocol;
    [Export("protocol", ArgumentSemantic.Retain)]
    string Protocol { get; set; }

    // @property (retain, nonatomic) NSDictionary * params;
    [Export("params", ArgumentSemantic.Retain)]
    NSDictionary Params { get; set; }

    // @property (assign, nonatomic) ACRCloudRecMode recMode;
    [Export("recMode", ArgumentSemantic.Assign)]
    ACRCloudRecMode RecMode { get; set; }

    // @property (assign, nonatomic) NSInteger requestTimeout;
    [Export("requestTimeout")]
    nint RequestTimeout { get; set; }

    // @property (assign, nonatomic) NSInteger prerecorderTime;
    [Export("prerecorderTime")]
    nint PrerecorderTime { get; set; }

    // @property (assign, nonatomic) _Bool keepPlaying;
    [Export("keepPlaying")]
    bool KeepPlaying { get; set; }

    // @property (copy, nonatomic) ACRCloudResultBlock resultBlock;
    [Export("resultBlock", ArgumentSemantic.Copy)]
    ACRCloudResultBlock ResultBlock { get; set; }

    // @property (copy, nonatomic) ACRCloudStateBlock stateBlock;
    [Export("stateBlock", ArgumentSemantic.Copy)]
    ACRCloudStateBlock StateBlock { get; set; }

    // @property (copy, nonatomic) ACRCloudVolumeBlock volumeBlock;
    [Export("volumeBlock", ArgumentSemantic.Copy)]
    ACRCloudVolumeBlock VolumeBlock { get; set; }

    // @property (copy, nonatomic) ACRCloudResultWithFpBlock resultFpBlock;
    [Export("resultFpBlock", ArgumentSemantic.Copy)]
    ACRCloudResultWithFpBlock ResultFpBlock { get; set; }
}

// @interface ACRCloudRecognition : NSObject
[BaseType(typeof(NSObject))]
interface ACRCloudRecognition
{
    // -(id)initWithConfig:(ACRCloudConfig *)config;
    [Export("initWithConfig:")]
    IntPtr Constructor(ACRCloudConfig config);

    // -(void)startPreRecord:(NSInteger)recordTime;
    [Export("startPreRecord:")]
    void StartPreRecord(nint recordTime);

    // -(void)stopPreRecord;
    [Export("stopPreRecord")]
    void StopPreRecord();

    // -(void)startRecordRec;
    [Export("startRecordRec")]
    void StartRecordRec();

    // -(void)stopRecordRec;
    [Export("stopRecordRec")]
    void StopRecordRec();

    // -(void)stopRecordAndRec;
    [Export("stopRecordAndRec")]
    void StopRecordAndRec();

    // -(NSString *)recognize:(char *)buffer len:(int)len;
    [Export("recognize:len:")]
    unsafe string Recognize(NSObject buffer, int len);

    // -(NSString *)recognize:(NSData *)pcm_data;
    [Export("recognize:")]
    string Recognize(NSData pcm_data);

    // -(void)recognize_fp:(NSData *)fingerprint resultBlock:(ACRCloudResultBlock)resultBlock;
    [Export("recognize_fp:resultBlock:")]
    void Recognize_fp(NSData fingerprint, ACRCloudResultBlock resultBlock);

    // -(NSString *)recognize_fp:(NSData *)fingerprint;
    [Export("recognize_fp:")]
    string Recognize_fp(NSData fingerprint);

    // +(NSData *)get_fingerprint:(char *)pcm len:(int)len;
    [Static]
    [Export("get_fingerprint:len:")]
    unsafe NSData Get_fingerprint(NSObject pcm, int len);

    // +(NSData *)get_fingerprint:(NSData *)pcm;
    [Static]
    [Export("get_fingerprint:")]
    NSData Get_fingerprint(NSData pcm);

    // +(NSData *)get_fingerprint:(char *)pcm len:(unsigned int)len sampleRate:(unsigned int)sampleRate nChannel:(short)nChannel;
    [Static]
    [Export("get_fingerprint:len:sampleRate:nChannel:")]
    unsafe NSData Get_fingerprint(NSObject pcm, uint len, uint sampleRate, short nChannel);

    // +(NSData *)get_fingerprint:(NSData *)pcm sampleRate:(unsigned int)sampleRate nChannel:(short)nChannel;
    [Static]
    [Export("get_fingerprint:sampleRate:nChannel:")]
    NSData Get_fingerprint(NSData pcm, uint sampleRate, short nChannel);

    // +(NSData *)resample:(NSData *)pcm sampleRate:(unsigned int)sampleRate nChannel:(short)nChannel;
    [Static]
    [Export("resample:sampleRate:nChannel:")]
    NSData Resample(NSData pcm, uint sampleRate, short nChannel);

    // +(NSData *)resample:(char *)pcm len:(unsigned int)len sampleRate:(unsigned int)sampleRate nChannel:(short)nChannel;
    [Static]
    [Export("resample:len:sampleRate:nChannel:")]
    unsafe NSData Resample(NSObject pcm, uint len, uint sampleRate, short nChannel);

    // +(NSData *)resample_bit32:(char *)pcm len:(unsigned int)bytes sampleRate:(unsigned int)sampleRate nChannel:(short)nChannel isFloat:(_Bool)isFloat;
    [Static]
    [Export("resample_bit32:len:sampleRate:nChannel:isFloat:")]
    unsafe NSData Resample_bit32(NSObject pcm, uint bytes, uint sampleRate, short nChannel, bool isFloat);
}

}

And Structs.cs:

using System;

namespace AcrCloudSdkIosBinding
{
    public enum ACRCloudRecMode : uint
    {
        remote = 0,
        local = 1,
        both = 2,
        advance_remote = 3
    }

    public enum ACRCloudResultType
    {
        error = -1,
        none = 0,
        audio = 1,
        live = 2,
        audio_live = 3
    }

    public enum HTTPResumeType
    {
        error = -1,
        resume = 0,
        restart = 1,
        success = 2
    }
}

Here is the source for it, the .a file can be found there too (libACRCloud_IOS_SDK.a). And Here is the cocoapod for it.

Solution

After a week of hacking at this, I found the solution. I opened the source code of the native project (Swift) in Xcode and noticed that it was referencing libc++.tbd. So all I had to do is set -lc++ in the Linker Flags for the referencing .a library in Visual Studio (Right click on the library -> Properties -> Linker Flags).

Also, make sure that you are giving the appropriate privileges in your info.plist that your library needs. It would just crash on me without giving any error before I set the privileges that it needed.

The tool that Cole Xia referenced is worth looking at too, because I had to manually pick out the interfaces I needed in the generated ApiDefinition.cs because it was filled with junk that I didn't need, and fix a few things with it too. So I gave him the bounty points for that. I guess the tool didn't work for this library because of the referencing libc++.tbd.