.net - Calling `Contains` method from C# dynamic type yields error - why? -

i simplified problem tiny program examples exact error receive during run-time.

you can copy-paste console application , see yourself.

using system.collections.generic;  namespace consoleapplication5 {     class program     {         static void main(string[] args)         {             var list = new list<mydataclass>()             {                 new mydataclass {a = 1, b = 1},                 new mydataclass {a = 3, b = 8}             };             var ops = new myoperationsclass();             ops.reallygreatoperation(list, list[0]);         }     }      public class mydataclass     {         public int { get; set; }         public int b { get; set; }          public void adddatapartstoeachother()         {             var c = + b;             = c;             b = c;         }     }      public class myoperationsclass     {         public void reallygreatoperation(object obj, object z)         {             dynamic x = obj;             if (x.contains(z)) //<-- gets error here..                 ((dynamic)z).adddatapartstoeachother();         }     } } 

so problem?

as understand dynamic keyword can used wildcard, if method exists called no problem. why not working me in scenario?

now, know can change work doing this:

public class myoperationsclass {     public void reallygreatoperation(object obj, object z)     {         dynamic x = obj;     //    if (x.contains(z)) //<-- gets error here..     //        ((dynamic)z).adddatapartstoeachother();         if (x.gettype().getmethod("contains").invoke(obj, new[] {z}))             ((dynamic)z).adddatapartstoeachother();     } } 

but said - wish understand why more "natural" way not working.. cause if 2nd way out of no choice - don't see point of dynamic in language anymore.

the actual error received:

an unhandled exception of type 'microsoft.csharp.runtimebinder.runtimebinderexception' occurred in system.core.dll

additional information: best overloaded method match 'system.collections.generic.list.contains(consoleapplication5.mydataclass)' has invalid arguments

for may find relevant add snippet of actual code:

case relationnavigation.relationnavigationmultiplicity.manytoone: {     var stringvalue = dto.propertiesdata[relationnavigation.propertyend.propertyinfo.name];     if (string.isnullorempty(stringvalue))         continue;      dynamic list = relationnavigation.propertyend.propertyinfo.getvalue(modelobj);      var relatedmodelids = stringvalue.split(',').select(int.parse).toarray();     foreach (var relatedmodelid in relatedmodelids)     {         var relatedmodel = getbyid(relationnavigation.propertyend.relatedtype, relatedmodelid);         if (relatedmodel == null)             continue;          if(!list.gettype().getmethod("contains").invoke(list, new[] { relatedmodel }))         //if (!list.contains(relatedmodel))             list.add(relatedmodel);         relationnavigation.relatedobjectpropertyend.propertyinfo.setvalue(relatedmodel, modelobj);     }     break; } 

thanks.

instead of

if (x.contains(z)) 

you need cast z dynamic:

if (x.contains((dynamic)z)) 

for more information on why needed, see here: method not being resolved dynamic generic type, think question duplicate of.

that said, using dynamic bad design. there better way using generics and/or interfaces.