如何在C＃中为动态创建的类型调用通用扩展方法

Question

The extension I wrote is as follows:

public static IEnumerable<T> Traverse<T>(this IEnumerable<T> source, Func<T, bool> predicate) where T : class,  new()
{
    ....
}

The class Sample shown below is created dynamically using Reflection TypeBuilder. The object instanced that I created run time is like:

public class Sample
{
    public Sample()
    {
        Children= new ObservableTestCollection<Sample>(this);
    }

    public Sample(IEnumerable<Sample> source)
    {
        Children= new ObservableTestCollection<Sample>(this, source);
    }

    public ObservableTestCollection<Sample> Children;
}

ObservableTestCollection above is derived by ObservableCollection

typeBuilder here below is built by Reflection TypeBuilder. What I like to do is :

var type = typeBuilder.CreateType();
var obj = Activator.CreateInstance(type);
var results = (IEnumerable<...>)(obj.GetProperty("Children").GetValue(obj)).Traverse(s=>s!=null);

The problem here is that I can not cast to IEnumerable, since the Type for Sample is the one created by reflection TypeBuilder. It means that there is no clear type for Sample in code.

So, I want to find out some way to cast generic IEnumerable<...> or invoke extension method of Traverse.

Thanks in advance.

Answer 1

Your ObservableTestCollection<T> has to implement type IEnumerable<T> or derive from a type which has that implementation to be able to use your extension method like this:

public class ObservableTestCollection<T> : IEnumerable<T>
{
    private Sample sample;
    private IEnumerable<Sample> source;

    public ObservableTestCollection(Sample sample)
    {
        this.sample = sample;
    }

    public ObservableTestCollection(Sample sample, IEnumerable<Sample> source)
    {
        this.sample = sample;
        this.source = source;
    }

    public IEnumerator<T> GetEnumerator()
    {
        throw new NotImplementedException();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        throw new NotImplementedException();
    }
}

Then you can reflect on it like this:

var obj = Activator.CreateInstance(typeof(Sample));
var pi = obj.GetType().GetProperty("Children");
var ct = Convert.ChangeType(obj, pi.PropertyType) as ObservableTestCollection<Sample>;
var results = (IEnumerable <Sample>)(ct as IEnumerable<object>).Traverse(s => s.Equals("1"));

I am using object for T but you can use whatever you need. Also, you would need to add some items to the Children property at runtime so you can traverse them using your extension-but I assume you know this.

EDIT

You edited your question and added this:

The problem here is that I can not cast to IEnumerable, since the Type for Sample is the one created by reflection TypeBuilder. It means that there is no clear type for Sample in code.

Does not matter, it will still work. Here is some code where I do not even mention Sample as a class but as a type created on the fly:

AssemblyName assemblyName
= new AssemblyName("MyDynamicAssembly");
AssemblyBuilder assemblyBuilder
    = AppDomain.CurrentDomain.DefineDynamicAssembly(
        assemblyName,
        AssemblyBuilderAccess.Run);
ModuleBuilder moduleBuilder
    = assemblyBuilder.DefineDynamicModule("MyDynamicModule");
TypeBuilder typeBuilder
    = moduleBuilder.DefineType("Sample");
var obj = Activator.CreateInstance(typeBuilder.CreateType());
var pi = obj.GetType().GetProperty("Children");
var ct = Convert.ChangeType(obj, pi.PropertyType) as IEnumerable<object>;
var results = (ct as IEnumerable<object>).Traverse(s => s.Equals("1"));