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dotnet clr : Reflection question about PropertyInfo
How do you take a PropertyInfo and get an instance of the object described by it? For example, I want to get the actual instance of the object described by "pi" in the snippet below (not the object's value like what GetValue() provides, but a reference to the object itself): MemberInfo[] arrayMemberInfo; Type t = tmptarget.GetType(); arrayMemberInfo = t.FindMembers(MemberTypes.Property, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.SetProperty, new MemberFilter(DelegateToSearchCriteria), "ReferenceEquals"); PropertyInfo pi = t.GetProperty(arrayMemberInfo[0].Name); Thanks in advance! Adam
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AdamM wrote: > How do you take a PropertyInfo and get an instance of the object described > by it? For example, I want to get the actual instance of the object > described by "pi" in the snippet below (not the object's value like what > GetValue() provides, but a reference to the object itself): > MemberInfo[] arrayMemberInfo; > Type t = tmptarget.GetType(); > arrayMemberInfo = t.FindMembers(MemberTypes.Property, > BindingFlags.Public | BindingFlags.NonPublic | > BindingFlags.Instance | BindingFlags.SetProperty, > new MemberFilter(DelegateToSearchCriteria), "ReferenceEquals"); > PropertyInfo pi = t.GetProperty(arrayMemberInfo[0].Name); You mean how do you go from a value like "pi" to a value like "t"? You don't. A Type value is a runtime description of a class. It's the runtime equivalent of a compiletime class, and a Type value is as distinct from an instance of the class as the compiletime class is distinct from an instance of the class. A PropertyInfo value is a runtime description of a property, which is a class member. To call GetValue, you need to supply an instance reference, like your "tmptarget". You can go from a PropertyInfo to its ReflectedType, which is the Type of the class which contains the property. You can go from a PropertyInfo to its DeclaringType, which is the Type of the class which contains the property. (If the ReflectedType is not the same as the DeclaringType, the ReflectedType inherited the member from the DeclaringType.) But you can't go from a PropertyInfo to an instance any more than you can go from a Type to an instance or from a compiletime class to an instance. All the pointers are one way, instance to type, not type to instances. -- ..NET 2.0 for Delphi Programmers <http://www.midnightbeach.com/.net> Delphi skills make .NET easy to learn
Hi Jon,
Thanks for the clarification. So my ultimate problem is that I have classes with some members that are SortedLists. At runtime, how can I use reflection to identify and retrieve the contents of these SortedList members and display/manipulate their contents? For example, my type (tmptarget) has a SortedList member called tmptarget.List. I want to enumerate through it's members and locate the SortedList (List) at runtime without knowing in advance the name of the SortedList. Perhaps I am approaching the problem wrong? Thanks! Adam [quoted text, click to view] "Jon Shemitz" <jon@midnightbeach.com> wrote in message news:4485089E.EF5B406C@midnightbeach.com... > AdamM wrote: > >> How do you take a PropertyInfo and get an instance of the object >> described >> by it? For example, I want to get the actual instance of the object >> described by "pi" in the snippet below (not the object's value like what >> GetValue() provides, but a reference to the object itself): > >> MemberInfo[] arrayMemberInfo; >> Type t = tmptarget.GetType(); >> arrayMemberInfo = t.FindMembers(MemberTypes.Property, >> BindingFlags.Public | BindingFlags.NonPublic | >> BindingFlags.Instance | BindingFlags.SetProperty, >> new MemberFilter(DelegateToSearchCriteria), "ReferenceEquals"); >> PropertyInfo pi = t.GetProperty(arrayMemberInfo[0].Name); > > You mean how do you go from a value like "pi" to a value like "t"? You > don't. > > A Type value is a runtime description of a class. It's the runtime > equivalent of a compiletime class, and a Type value is as distinct > from an instance of the class as the compiletime class is distinct > from an instance of the class. > > A PropertyInfo value is a runtime description of a property, which is > a class member. To call GetValue, you need to supply an instance > reference, like your "tmptarget". > > You can go from a PropertyInfo to its ReflectedType, which is the Type > of the class which contains the property. You can go from a > PropertyInfo to its DeclaringType, which is the Type of the class > which contains the property. (If the ReflectedType is not the same as > the DeclaringType, the ReflectedType inherited the member from the > DeclaringType.) > > But you can't go from a PropertyInfo to an instance any more than you > can go from a Type to an instance or from a compiletime class to an > instance. All the pointers are one way, instance to type, not type to > instances. > > -- > > .NET 2.0 for Delphi Programmers <http://www.midnightbeach.com/.net> > > Delphi skills make .NET easy to learn > Just printed, and shipping now.
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AdamM wrote: > So my ultimate problem is that I have classes with some members that are > SortedLists. > At runtime, how can I use reflection to identify and retrieve the contents > of these SortedList members and display/manipulate their contents? For > example, my type (tmptarget) has a SortedList member called tmptarget.List. > I want to enumerate through it's members and locate the SortedList (List) at > runtime without knowing in advance the name of the SortedList. > > Perhaps I am approaching the problem wrong? Perhaps. Quickly (because I have to get up at 5, to volunteer all days at the polls tomorrow) you could certainly use Type.FindMembers to find all fields and/or properties of type SortedList. -- ..NET 2.0 for Delphi Programmers <http://www.midnightbeach.com/.net> Delphi skills make .NET easy to learn
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"Jon Shemitz" <jon@midnightbeach.com> wrote in message news:4485221F.8F1C9ADE@midnightbeach.com... > AdamM wrote: > >> So my ultimate problem is that I have classes with some members that are >> SortedLists. >> At runtime, how can I use reflection to identify and retrieve the >> contents >> of these SortedList members and display/manipulate their contents? For >> example, my type (tmptarget) has a SortedList member called >> tmptarget.List. >> I want to enumerate through it's members and locate the SortedList (List) >> at >> runtime without knowing in advance the name of the SortedList. >> >> Perhaps I am approaching the problem wrong? It sounds as if you are looking for some mixture of PropertyInfo (or PropertyDescriptor) and delegates, that captures the object instance and all its type descriptor information. I've added delegates because I think they will be far faster than calling PropertyInfo.GetValue() for instance. With generics, this really isn't too hard to accomplish (not tested): class PropertyDelegate<S, T> { private readonly S instance; private readonly PropertyInfo prop; private delegate T GetAccessor(); private delegate void SetAccessor(T value); private readonly GetAccessor getter; private readonly SetAccessor setter; public PropertyDelegate(S for, PropertyInfo propinfo) { instance = for; prop = propinfo; if (!propinfo.DeclaringType.IsAssignableFrom(typeof(S))) throw new ClassCastException(); if (!typeof(T).IsAssignableFrom(propinfo.PropertyType) throw new ClassCastException(); getter = (GetAccessor)Delegate.CreateDelegate(typeof(GetAccessor), for, propinfo.GetGetMethod(), false); setter = (SetAccessor)Delegate.CreateDelegate(typeof(SetAccessor), for, propinfo.GetSetMethod(), false); } public T Value { get { return getter(); } set { setter(value); } } public string Name { get { return prop.Name; } } } [quoted text, click to view] > > Perhaps. Quickly (because I have to get up at 5, to volunteer all days > at the polls tomorrow) you could certainly use Type.FindMembers to > find all fields and/or properties of type SortedList. > > -- > > .NET 2.0 for Delphi Programmers <http://www.midnightbeach.com/.net> > > Delphi skills make .NET easy to learn > Just printed, and shipping now.
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