c# binaryformatter - i out category binary data?

i wish deserialize an vigilant nonetheless don't know category adult front. so, cruise following code...

iformatter formatter = new binaryformatter();
stream tide = new filestream("myfile.bin", filemode.open, fileaccess.read, fileshare.read);
myobject obj = (myobject)formatter.deserialize(stream);

what i i don't know category adult front? say, instance "myfile.bin" myobject myfoo. i establish vigilant instantiate?

something like...

if (magic happens here == typeof(myobject))  
    myobject obj = (myobject) formatter.deserialize(stream);   
else (more incantation happens here == typeof(myfoo))  
    myfoo foo = (myfoo)formatter.deserialize(stream);