I'm using a 3rd party lib to do some work. I'm passing an object to the lib and it performing some actions on each property of the object. It enumerates properties using reflection. This is how it implemented and I can't change it.
I don't know which and how many properties should be processed by the lib at compile-time. This information only available at run-time. So I can't create class declaration in my source code.
It seems dynamic feature of .net4 can't help me because lib using reflection, not dynamic.
Actually I can see only two options here:
Create a huge class definition like this:
class Data
{
public object P1 {get; set;}
public object P2 {get; set;}
....
public object PN {get; set;} // N should be at least 10.000
}
Generate class definition at runtime and use CSharpCodeProvider to compile an use it.
Can you suggest me any other options?
And sadly, I can't replace this lib with another one.
Using the first approach will lead to high memory consumption. I would have chosen use TypeBuilder class to create new types at the runtime.
What you're looking for is known as a Property Bag. You may be able to implement something like this by using ICustomTypeDescriptor to expose additional metadata (assuming your library supports it).
If your consuming library is using Reflection directly (and not taking advantage of designer features like Type Descriptors) then your best bet is probably dynamic generation of a proxy wrapper with the additional properties. Castle DynamicProxy is one good way to do this.
EDIT:
Actually, I'm not sure if Castle supports adding new properties to the proxy object. You might be stuck using IL Emit directly via TypeBuilder. This is non-trivial, as you'll need to learn enough about IL Emit to generate the property accessors and there's a bit of a learning curve. That said, it's interesting and fun stuff and worth the effort if you have the time.
I guess it's about regular GUI element like Grid or PropertyGrid.
Then I would start from reflecting grid's method that accept class instance as parameter, and if it is possible fill internal Dictionary<PropertyInfo, instance> or Dictionary<Name,Value> with my own vales.
If this is impossible, instead of Emit, try to use System.CodeDom:
Link
Related
I was looking at using DynamicProxy classes, and I'm fairly new to this concept. Before I got too far down this road, I was wondering how well these classes work with IntelliSense and type safety?
I'm just afraid of using something like Castle DynamicProxy (or some other ones), and after setting everything up finding out that using my objects provides no IntelliSense or type safety. Can anyone shed any light on this?
I'm looking for a straight answer on how DynamicProxy classes are
used, and whether or not they support intellisense, and if so... how?
Well, in explaining how DynamicProxy classes work, you'll have a clear understanding to why they are type safe, and how they are able to work with intellisense so nicely.
Firstly, let's understand what a DynamicProxy actually is. A proxy class is a class that handles member calls on behalf of another class. This is either done through inheritance (most common) or through composition. So, if you were to hand-write a proxy class, here is what it could look like:
public class Customer
{
public virtual string Name { get; set; }
// etc...
}
public class CustomerProxy : Customer
{
public override string Name
{
get
{
// Do additional functionality...
return base.Name;
}
set
{
// Do additional functionality...
base.Name = value;
}
}
}
Two (2) key features play a crucial role in this working appropriately, inheritance and polymorphism. So, to use the Customer class seamlessly, a ProxyGenerator simply would create an instance of the CustomerProxy class, but return it as a type of Customer. It would basically be the same thing as doing Customer customer = new CustomerProxy();. The "dynamic" portion doesn't really have anything to do with the .NET dynamic keyword, but instead should read "Runtime", because it simply means that the proxy class is generated at runtime (while the application is running), instead of at compile-time. Oh, and in case you are wondering how it does this, it uses System.Reflection.Emit
That's the simple version of what a DynamicProxy is. Different frameworks offer different features when it comes to creating these proxy classes. For example, in Castle Windsor's DynamicProxy one could create Mixins and apply additional interfaces to these proxy classes -- that is, your generated proxy class could potentially look something like this: public class CustomerProxy : Customer, ISomeInterface { ... }, even though the Customer class itself did not implement the ISomeInterface. Here is a really good resource for Castle's DynamicProxy (http://kozmic.net/dynamic-proxy-tutorial/). It goes through the various features and use cases for those features.
It is and type safe so intellisense should work just fine with it.
see this example: DynamicProxy tutorial
you can see that they use generics for instanciating the proxy classes. It means that its fully typed so you've got nothing to worry about.
Proxies can be seen as call interceptors (depending of the kind of proxy implementation), so when you are writing your code is like you were working with a defined interface or class so you will get intelliSense.
Then, depending of the kind of proxy you implement "some" calls to the class/interface members will be intercepted.
[Edit]
If you use the dynamic keyword, for example when implementing a dynamic proxy using a DynamicObject obviously you will not have intelliSense, but this caused by the nature of the dynamic keyword and not by the proxy itself. You can take a look at this link to see how to implement a Proxy using a DynamicObject
So I've got this boilerplate code that I want to apply to a bunch of properties of certain classes, that is essentially identical for each one. Rather than have to type this same code out again and again for all of these properties, I was wondering if there was any way I could dynamically build these property methods either post-compile or at runtime, by assigning a C# attribute to the property that includes the slight difference for each method (a string) and then finding these properties by reflection.
I'm aware of PostSharp, but I'm looking for something free or open source.
For example, instead of having to do this:
public string Name {
get { return _member.GetValue( "othername" ); }
set { _member.SetValue( "othername", value ); }
}
...for each property I have, I just want to say this:
[MapTo( "othername" )]
public string Name { get; set; }
Any thoughts?
You can use Mono.Cecil for dynamic code injection.
You can make these properties as virtual and generate class that overrides these properties and compile new class to assembly where overridden properties will be defined. Then you should create instance of dynamic generated class and used it as defined class.
You can do something similar using the Unity interception extension.
OK, so it probably merits its own answer. I am aware of the following AOP Frameworks for which you won't have to pay:
Castle Dynamic Proxy
Introducing LinFu, Code
Looks like you are looking for an AOP (Aspect Oriented Programming) like PostSharp.
It allows you to programatically inject code (just like you mentioned) and is very flexible.
Check out CInject on Codeplex which is an open-source alternative to code injection
Is there a way for me to change the properties a class has (add/remove properties) on runtime?
You cannot do this unless you are working with an instance of ExpandoObject. The metadata for a CLR type is fixed in the assembly and cannot be changed at execution time. If you really need this kind of dynamic behavior you must use a dynamic type (like EpandoObject) that supports this behavior.
Just to add to Andrew Hare's reply: With C# 4 and .NET 4 you can inherit from DynamicObject and redefine what it means to take various actions on an instance of the type. DynamicObject defines a number of virtual methods that you can override to take control of what it means to e.g. access a property. You could use this to allow properties to be added/removed to the instance, which is pretty much what ExpandoObject does.
For more about ExpandoObject see this question and this blog post.
You could create your types at runtime using System.Reflection.Emit -link
For UI development (i.e. what is presented to the end user) look at implementing ICustomTypeDescriptor (in System.ComponentModel). Many controls are aware of this interface and will use it to query the properties an instance or type exposes.
If you are on 3.5 you can use IL to create a dynamic type, and also accomplish the task, but it's a lot harder, but there are some frameworks for doing that I suppose.
I don't understand, why use dynamic MethodBags when I can use ExpandoObject? What am I missing here?
MethodBags and analogous implementations tend to have some limitations. It may be easier just to implement your own class if you find yourself running into these roadblocks. Specifically:
Hard to implement state in a method bag. (Expression trees cannot contain objects that are statically typed as dynamic; no good syntax to create methods that rely on internal state on the same dynamic object.)
Can only add public methods. No virtual, private, protected, or abstract methods.
Can't implement an interface.
In comparison, ExpandoObjects are true classes and are much richer and more full-featured. They more closely mimic what you'd otherwise get for free in, say, Ruby or Python.
Quick note: for those who don't know, dynamic method bag is a technique for adding methods dynamically to an object. Bill Wagner describes it here with source code here.
The simple answer is that the MethodBag concept is just showing you a technique. You can absolutely use the ExpandoObject to do this, but there may be a time when you want to write your own class that inherits from System.Dynamic.DynamicObject. An example of this might be to provide a dynamic JSON, YAML, or XML object that lets you reference your data in dot-properties-notation rather than in the traditional stringy ways. If you inherit from DynamicObject, you may find that you want to allow the addition of dynamic functions to your class too. The MethodBag technique shows you how to do that. The ExpandoObject is just one example of a class that implements this technique. ExpandoObject will be good for 95% of what you need, and the MethodBag technique shows you how to custom write your own when you decide to do that for the last 5%.
Is there any way to add Field (or FieldInfo, maybe this is the same) to a class at runtime?
You can't alter a class definition at runtime. However, you can create a new class that inherits from the original class (if it's not sealed) and declares the field. You can do this by emitting the appropriate IL code using System.Reflection.Emit.
No, C# doesn't allow monkey-patching.
You can generate new classes using either CodeDOM or Reflection.Emit, but you can't modify existing ones.
C# does not allow it because all of it's classes are based on Metadata. The CLR (not C#) disallows the adding of fields to metadata at runtime (1). This is the only way that C# would be able to add a field at runitme.
This is unlike dynamic langauges such as IronPython which essentially don't have concrete metadata classes. They have more dynamic structures which can be altereted at runtime. I believe IronPython simply keeps it's members (fields and methods) in what amounts to a hashtable that can be easily altered at runtime.
In C# 3.0, your best resource is to use Reflection.Emit. But this will generate an entirely new class vs. altering an existing one.
(1) There are certain APIs such as the profiling APIs or ENC that allow this but I'm not sure if their capabalities expand to adding fields.
See this question for a simple way to do it in C# 4.0, by casting an ExpandoObject as an IDictionary, which causes the values added to the dictionary to become properties of the object. I demonstrate this in another answer of mine showing that they actually become properties.
However, this is only possible with an instance of ExpandoObject or by sub-classing DynamicObject.
It may also be possible to use with other classes if they implement IDynamicMetaObjectProvider, but I think there is too much work involved to get it to work properly.
Not exactly.
However, you can implement ICustomTypeDescriptor to approximate it, and then just use a hashtable to store the fieldname/value pairs. A lot of the framework which uses reflection asks for ICustomTypeDescriptor first.
Not until C# 4.0 which adds dynamic lookup and is based on the CLR 4.0 which incorporates the DLR, and then it will not strictly be adding to a class, as classes won't be in the picture.
as others already said, this isn't possible. What is the reason for your question? If you need to store some additional data in the class dynamically, then you could probably just use dictionary:
class My {
Dictionary<string, object> data;
public My() { data = new Dictionary<string, object>(); }
}
.. but it really depends on what you actually want to achieve?
Perhaps you could use the Decorator pattern.
In object-oriented programming, the decorator pattern is a design pattern that allows behavior to be added to an individual object, either statically or dynamically, without affecting the behavior of other objects from the same class.
http://www.dofactory.com/Patterns/PatternDecorator.aspx