CODEWITHSUNDEEP
c#dynamicreflection
Tono Nam
Tono Nam

Reputation: 36048

Why reflection does not find property

I have the class:

    class Person 
    {
        public string Name { get { return "Antonio"; } }
    }

and the Code:

        IEnumerable<object> uncknownObject;

        uncknownObject = new ObservableCollection<Person>( );

        var observCol = uncknownObject.GetType( );

        var x = ( ( dynamic )observCol ).GenericTypeArguments[ 0 ];

        var y = observCol.GetProperty( "GenericTypeArguments" );

        var instance = ( Person )Activator.CreateInstance( x );

        Console.WriteLine( instance.Name ); // Print Antonio!!!

why does y == null ?

Note the picture:

enter image description here

the debugger shows that the property GenericTypeArguments should exist and the code shows the opossite. It can be proven that the debugger is right and that property exist because then how come x is not null. If that property exists then why y is equal to null!!!???

Edit

Thanks to Ani I now have:

        IEnumerable<object> uncknownObject;

        uncknownObject = new ObservableCollection<Person>();

        var observCol = uncknownObject.GetType();

        var genTypeArgsProperty = typeof(Type).GetProperty("UnderlyingSystemType");

        var genTypeArgsValue = (genTypeArgsProperty.GetValue(observCol, null));

        var f = genTypeArgsValue.GetType().GetMethod("GetGenericArguments");

        IEnumerable<object> result = (IEnumerable<object>)f.Invoke(genTypeArgsValue, null);

        var x = result.FirstOrDefault();

        var instance = Activator.CreateInstance(  (Type)x );

In case of curios why I needed that functionality click here

Upvotes: 3

Views: 2091

Answers (2)

Frank59
Frank59

Reputation: 3261

This code works with net framework 4: 

        IEnumerable<object> uncknownObject;

        uncknownObject = new ObservableCollection<Person>();



        var observCol = uncknownObject.GetType();

        var x = ((dynamic) observCol).UnderlyingSystemType.GetGenericArguments()[0];

        var y = observCol.GetGenericArguments();

        var instance = (Person)Activator.CreateInstance(x);

        Console.WriteLine(instance.Name); // Print Antonio!!!

Upvotes: 3

Ani
Ani

Reputation: 113402

I don't really understand what you're trying to accomplish with all this meta-meta-reflection, but you seem to have misunderstood what Type.GetProperty does. It gets meta-data for a property on the actual type represented by the System.Type instance (in this case, ObservableCollection<Person>). It does not get meta-data for a property declared on System.Type itself, unless of course you call it on a System.Type representing System.Type itself.

In your case, y is null since ObservableCollection<Person> does not have a property named "GenericTypeArguments".

Try this instead:

var genTypeArgsProperty = typeof(Type).GetProperty("GenericTypeArguments");

var genTypeArgsValue = (Type[]) (genTypeArgsProperty.GetValue(observCol, null));

var onlyTypeArgValue = genTypeArgsValue.Single();

Upvotes: 4

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