ML.Net 在 Xamarin.Android 上工作但不在 Xamarin.iOS 上工作：System.Reflection.Emit

Question

I have a .NETStandard 2.1 solution running a Xamarin.Forms solution. While trying to do some ML work (predicting anomalies), I am getting an runtime exception ONLY in Xamarin.iOS.

System.PlatformNotSupportedException with a message that the "Operation is not supported on this platform." Here's my code:

// Dataset for ML
var amounts = new int[] { 100, 150, 200, 300, 250, 3000, 100, 250, 300, 250 };
var withdrawals = amounts.Select(amount => new Withdrawal { Amount = amount }).ToList();

// Instantiate ML context
var mlContext = new Microsoft.ML.MLContext();

// Create you algorithm
var estimator = mlContext.Transforms.DetectIidSpike( // "using ML;" needed for this statement
    outputColumnName: nameof(Prediction.Output),
    inputColumnName: nameof(Withdrawal.Amount),
    confidence: 99,
    pvalueHistoryLength: amounts.Length/2);

// Link data to algorithm
var amountsData = mlContext.Data.LoadFromEnumerable(withdrawals); // <=THE LINE THROWING THE EXCEPTION
var transformedAmountsData = estimator.Fit(amountsData).Transform(amountsData);

// Create output
var predictions = mlContext.Data.CreateEnumerable<Prediction>(transformedAmountsData, reuseRowObject:false).ToList();

foreach (var prediction in predictions)
{
    var isAnomaly = prediction.Output[0];
    var originalValue = prediction.Output[1];
    var confidenceLevel = prediction.Output[2];
    Console.WriteLine($"{originalValue} {confidenceLevel} {isAnomaly}");
}

And these are the two model objects:

class Withdrawal
{
    public float Amount { get; set; }
}

class Prediction
{
    [Microsoft.ML.Data.VectorType]
    public double[] Output { get; set; }
}

Here's the stacktrace:

at System.Reflection.Emit.DynamicMethod..ctor (System.String name, System.Type returnType, System.Type[] parameterTypes, System.Type owner, System.Boolean skipVisibility) [0x00006] in /Library/Frameworks/Xamarin.iOS.framework/Versions/Current/src/Xamarin.iOS/mcs/class/corlib/System.Reflection.Emit/DynamicMethod.notsupported.cs:64 \\n at Microsoft.ML.ApiUtils.GeneratePeek[TOwn,TRow,TValue] (System.Reflection.PropertyInfo propertyInfo, System.Reflection.Emit.OpCode assignmentOpCode) [0x00040] in <ac1708cf77ce4a63b733a786896eec8e>:0 \\n at (wrapper managed-to-native) System.Reflection.RuntimeMethodInfo.InternalInvoke(System.Reflection.RuntimeMethodInfo,object,object[],System.Exception&)\\n at System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x0006a] in /Library/Frameworks/Xamarin.iOS.framework/Versions/Current/src/Xamarin.iOS/mcs/class/corlib/System.Reflection/RuntimeMethodInfo.cs:395

I understand from the official Xamarin.iOS docs that System.Reflection.Emit is not supported. So my question is that is there any way that I can make this work?

I know the Xamarin book by Jonathan Peppers, mentions to use "NO_LCG" to the Define Symbols field to get rid of the same error and make Ninject work on Xamarin.iOS. That didn't work for this case though, but is there something similar to go around it?

Answer 1

I couldn't figure out where you got that from!

If you execute mtouch yourself, you can find a number of options that are not well documented in the standard Microsoft guides and for "experimental" features, this is doubly true:

mtouch --help

interpreter:

  --interpreter[=VALUE]  Enable the *experimental* interpreter. Optionally
                           takes a comma-separated list of assemblies to
                           interpret (if prefixed with a minus sign, the
                           assembly will be AOT-compiled instead). 'all'
                           can be used to specify all assemblies. This
                           argument can be specified multiple times.