How to I get reference to generic singleton instance using only System.Type/reflection

Question

I created a simple performance testing class that is a singlton and it uses generics PerformanceTesting<T>.Instance

(Full source code available on my blog post, but it is not the most up to date version http://www.createdbyx.com/post/2013/03/27/Code-Snippets-12-%E2%80%93-Performance-Testing.aspx )

This allows the developer to use what ever they are more comfortable using as the accessor key whether it be a string, integer or enum etc.

So everything worked great but I am attempting to build a performance reporting window and I want the ability to collect performance data from all the instanciated singlton instances wheather it be PerformanceTesting<int> or PerformanceTesting<string> etc.

The only way I figure I can do this is through the use of reflection. I should also mention that the PerformanceTesting class makes use of another class to track the various types that are being used as accessor keys to the PerformanceTesting<T> singleton(s).

    /// <summary>
    /// Provides a lock object when a singleton reference need to be instantiated.
    /// </summary>
    private static object lockObject = new object();

    /// <summary>
    /// Gets a singleton instance of the <see cref="PerformanceTesting{T}"/> class.
    /// </summary>
    public static PerformanceTesting<T> Instance
    {
        get
        {
            if (singleton == null)
            {
                lock (lockObject)
                {
                    singleton = new PerformanceTesting<T>();
                    PerformanceTestingTypes.Register<T>(); 
                }
            }

            return singleton;
        }
    }

A stripped down simplified version of PerformanceTestingTypes class is ...

public class PerformanceTestingTypes
{
    private static PerformanceTestingTypes singleton;
    private List<Type> types = new List<Type>();

    public static PerformanceTestingTypes Instance
    {
        get
        {
            return singleton ?? (singleton = new PerformanceTestingTypes());
        }
    }

    public static Type[] GetTypes()
    {
        var values = new Type[Instance.types.Count];
        Instance.types.CopyTo(values, 0);
        return values;
    }

    public static void Register<T>()
    {
        Instance.types.Add(typeof(T));
    }

    // can't return PerformanceTesting<T> because T is of System.Type not the actual accessor type.
    public static PerformanceTesting<T> GetTesting<T>(T type)
    {
        var rootType = typeof(PerformanceTesting<>); // this is wrong but placed for example purposes!!!

        var prop = rootType.GetProperty("Instance");
        var reference = prop.GetGetMethod().Invoke(null, null);

        return reference; // compile error because Invoke returns type System.Object
    }
}

I am using this method to try and report out the results to the debug log ...

   /// <summary>
    /// If the PERFORMANCE symbol is available will report the performance metric information out to the console.
    /// </summary>
    public static void ReportPerformanceTimes()
    {
        var result = string.Empty;
        foreach (var type in PerformanceTestingTypes.GetTypes())
        {
             var perf = PerformanceTestingTypes.GetTesting(type);

            var keyNames = PerformanceTestingTypes.GetKeyNames(type);

            foreach (var name in keyNames)
            {
                var key = PerformanceTestingTypes.ConvertKey(name, type);
                result += string.Format("{0} - Total: {1}ms Average: {2} Count: {3}\r\n", name, perf.TotalMilliseconds(key), perf.AverageMilliseconds(key), perf.GetStartCount(key));
            }

            result += string.Format("Total Performance Times - Total: {0}ms", perf.TotalMilliseconds(perf.GetKeys()));
        }

         Debug.Log(result);
    }

My problem I'm having lies within the PerformanceTestingTypes.GetTesting() method. I need to return a reference to a specific instance of a generic singleton using only a System.Type that references the actual type that the singleton uses as it's accessor key.

var type = typeof(int); // the accessor key type that was used
// from the 'type' variable get a reference to singleton 
var reference = PerformanceTesting<int>.Instance;

Or to put it another way how would I use reflection to get the type for PerformanceTesting<int> if all I have is a variable 'type' that is a System.Type that refers to int.

Technically I thought I could try and just create and build a single C# class inside of a string and compile that string into a in memory assembly then call the class to get the reference to the singleton I need but it seems overkill and I suspect I may run into the same or similar issues as well as with casting.

Is this even possible or am I trying to do the impossible? Hope my question makes sense. My brain has decided to take a hiatus on this one. :(

Answer 1

Try this:

var performanceTestingType = typeof(PerformanceTesting<>);
Type[] typeArgs = { typeof(int) };
var genericType = performanceTestingType.MakeGenericType(typeArgs);
object performanceTestingOfTypeInt = Activator.CreateInstance(genericType);

MSDN article here

Answer 2

For those of you who landed on this page looking for a similar answer I am providing the resulting method for how I achieved my goal thanks to jaywayco's answer.

    private void DrawPerformanceMetricsFlatList()
    {
        foreach (var type in PerformanceTestingTypes.GetTypes())
        {
            var performanceTestingType = typeof(PerformanceTesting<>);
            Type[] typeArgs = { type };
            var genericType = performanceTestingType.MakeGenericType(typeArgs);

            var data = genericType.GetProperty("Instance", BindingFlags.GetProperty | BindingFlags.Static | BindingFlags.Public).GetGetMethod().Invoke(null, null);
            var totalMilli = data.GetType().GetMethod("TotalMilliseconds", new[] { type });
            var avgMilli = data.GetType().GetMethod("AverageMilliseconds", new[] { type });
            var totalTicks = data.GetType().GetMethod("TotalTicks", new[] { type });
            var avgTicks = data.GetType().GetMethod("AverageTicks", new[] { type });
            var startCount = data.GetType().GetMethod("GetStartCount", new[] { type });
            var fromConverter = data.GetType().GetProperty("ConvertFromStringCallback");
            // var toConverter = data.GetType().GetProperty("ConvertToStringCallback", new[] { type });
            var func = fromConverter.GetGetMethod().Invoke(data, null);
            var invoker = func.GetType().GetMethod("Invoke");

            var keyNames = PerformanceTestingTypes.GetKeyNames(type);

            switch (this.sortIndex)
            {
                case 1:
                    keyNames = keyNames.OrderBy(x => x).ToArray();
                    break;

                case 2:
                       keyNames = keyNames.OrderByDescending(x => totalTicks.Invoke(data, new[] { invoker.Invoke(func, new[] { x }) })).ToArray();
                    break;

                case 3:
                         keyNames = keyNames.OrderByDescending(x => avgTicks.Invoke(data, new[] { invoker.Invoke(func, new[] { x }) })).ToArray();
                    break;

                case 4:
                        keyNames = keyNames.OrderByDescending(x => startCount.Invoke(data, new[] { invoker.Invoke(func, new[] { x }) })).ToArray();
                    break;
            }

            ControlGrid.DrawGenericGrid((items, index, style, options) =>
            {
                var value = items[index];
                var selected = GUILayout.Toggle(this.selectedIndex == index, value, style);
                if (selected)
                {
                    this.selectedIndex = index;
                    var key = invoker.Invoke(func, new[] { value }); 
                    this.performanceData = string.Format("{0}\r\nTotal: {1}ms ({4} ticks)\r\nAverage: {2}ms ({5} ticks)\r\nCount: {3}\r\n", value,
                        totalMilli.Invoke(data, new[] { key }),
                        avgMilli.Invoke(data, new[] { key }),
                        startCount.Invoke(data, new[] { key }),
                        totalTicks.Invoke(data, new[] { key }),
                        avgTicks.Invoke(data, new[] { key }));
                }
                return value;
            }, keyNames, 1, GUI.skin.button);
        }
    }