I'd like to store a variable of type Actor in a variable which is of a BP interface type.
Is there something like a Cast To BP Interface BP node? I know about the Does Implement Interface (which does not return a reference to the interface instance) and the Cast To (which doesn't work for interfaces) nodes. But these do not allow me to get an instance of my BP interface type.
I know that I could store the actor in a variable of type Actor and then invoke the interface functions on that actor. But that seems like a type system workaround to me. That's why I'd like to enfore the interface type on the variable.
Cast To does work, it just doesn't show up in the context. Disable 'Context Sensitive' or click in an empty place in the graph to create a Cast To node, and then hook it up to your actor.
(Answered on behalf of #Rotem)
Related
I have seen is possible to instantiate an object who implements an interface instead of a class. I´d like to know what are the benefits of this.
I attach an example :
Interface just tells the program, that this object it just received has these methods defined. So you can have multiple different classes implement the same interface. And when a method accepts a given interface, then it can accept all the classes that implement the interface.
By instansiating a class into interface, you are saying, that whatever following code does, it cares only about the methods stated in the interface.
If you instansiate into class type, you are saying you want only this spesific type and none else.
I have use the type dynamic, a new type in .NET 4.0.
I want to use a dynamic type because I want to use some types that in advance I don't know what type is, but I know that all this possible type has some common methods.
In my case, I am using self tracking entities in entity framework 4.0, and I know that all the entities has the methods markedXXX (to set the state of the entity).
Through the dynamic object that I created, I can access and set the properties of one of this entities, but when I try to execute the MarkedAsXXX method I get an exception that says that the object has not definied the method.
I would like to know how to access to this methods. Is it possible?
Because I have a function that can access to the original values and set this values to the current one, but I need to set the entity as Unchenged.
Thanks.
I want to use a dynamic type because I want to use some types that in advance I don't know what type is, but I know that all this possible type has some common methods.
That suggests you should create an interface with those common methods, and make all the relevant types implement the interface.
Through the dynamic object that I created, I can access and set the properties of one of this entities, but when I try to execute the MarkedAsXXX method I get an exception that says that the object has not defined the method.
It's possible that this is due to explicit interface implementation. If the types have those methods declared as public methods in the normal way, it should be fine.
If you really want to use dynamic typing with these types, is there some base interface which declares the MarkedAsXXX methods, which you could cast the objects to before calling those methods? (I'm not familiar with the entity framework, so I don't know the details of those methods.)
Basically, I would try to avoid dynamic typing unless you really need it, partly because of edge cases like this - but if explicit interface implementation is the cause, then casting to that interface should be fine.
If you define an interface to the dynamically generated classes you can call the methods without the hassle of reflection calling.
I have an interface ISettings. Many classes will implement this interface. I want to be able to kernel.GetService(typeof(MySettings)) and have it call the type be created from a method.
I want to avoid using a type finder to pre-bind all ISettings implementations. I would like to be able to intercept GetService() calls to check if the type is of ISettings. If so, I want to provide a binding for it (method).
What can ninject do for me?
When running FxCop I get the error that interface methods should be callable by child types.
The resolution states the following:
"Make 'MenuPreview' sealed (a breaking change if this class has previously shipped),
implement the method non-explicitly, or implement a new method that exposes
the functionality of 'IComponentConnector.Connect(int, object)'
and is visible to derived classes."
I get this for all classes the derive from Window or some other UI class. Is this a red herring that I can ignore, or is there something I should be doing?
I think the issue is that if an interface is implemented explicitly, it will be impossible for a derived class to both change the interface behavior and make use of the base-class behavior. A common pattern to get around this difficulty in cases where explicit interface implementation would be required is to have the interface do nothing but call a protected virtual method, and have any derived classes that wish to override the behavior of the interface do so by means of the protected virtual method.
Consider IDisposable.Dispose(). If the code in an explicit implementation were actually responsible for performing the disposal, there would be no way for a derived class to add its own dispose logic except by reimplementing IDisposable, and there would be no way for a class which reimplemented IDisposable to access its parent's Dispose method. Although Microsoft could have had IDisposable.Dispose call a protected function with a different name, it opted to use the same name but add a dummy parameter of type Boolean.
I would like to pass an interface to a method signature which takes Object as its parameter, so I wonder about this question
public Stream GetViewStream(string viewName, object model, ControllerContext context)
instead of object I shall like to pass an interface Imodel, without modifying the signature. Is there a base class for interfaces?
Also in the new mvc2 is there a way to avoid controllercontext altogether?
I'd only answer the first question - Why there's no common base interface for all interfaces ?
First of all, there's no common pre-defined base interface for all interfaces, unlike the System.Object case. Explaining this can get very interesting.
Let us assume, you could have a common interface for all interfaces in the system. That means, all interfaces will need to force their implementations to provide implementation-details for that common base interface. In general, interface are used to give specific special behaviors to their concrete implementation classes. Obviously you only want to define an interface when you only know what to do and don't know HOW to do that. So, if you let there be a common base interface for all interface and force the implementations to expect them to provide details of how to do it - why would you want to do it ? What common task each class should do that varies from one another ?
Lets look at the other side of the coin, why we have System.object as base class of any .Net type - It is simple it gives you some methods that have COMMON implementation for any .Net type and for those methods that it might vary from type-to-type they have made it virtual ex: .ToString()
There's possibly no assumption of any
system-wide interface method which is
virtual/abstract to all its
implementations.
One common practice of using Interface is say, defining a particular behavior to any type. Like I'd have an interface IFlyable which will give Fly() to all types that implement IFlyable. This way I can play with any Flyable object regardless of its inheritance hierarchy coming into picture. I can write a method like this..
public void FlyTheObject(IFlyable flyingObject)
{
flyginObject.Fly();
}
It does not demand anything from the object but the implementation of the Fly() method.
EDIT
Additionally, All interfaces will resolve to Object because interfaces cannot be instantiated. The object is always of a concrete class that can be instantiated. This class may or may not implement your interface but as we know, any .Net type is ultimately based to System.Object, so you will be able to take the instance into an object type regardless of the fact if it implements a particular interface or not.
No, there is no base class for interfaces. Nor there is base interface for interfaces.
As for your second question (and partly first one) - what are actually you trying to do?
There is no base class for interfaces, but you can pass any interface variable e.g:
private IEnumerable<int> myInterfaceVariable = new List<int>();
to your method because by definition anything that is stored in that variable must be an instance of a class that inherits from the interface - therefore it must be an object.
The following compiles fine:
public class InterfaceAsObject
{
private IEnumerable<int> myInterfaceVariable = new List<int>();
private void CallDoSomething()
{
DoSomething(myInterfaceVariable);
}
private void DoSomething(object input)
{
}
}
Re 1, there is no base interface, but if I understand you correctly, you can achieve what I think you want by just passing your object that implements IModel via the model parameter and cast (and check!) the parameter to IModel. I use 'as' and check for null.
If you don't need total flexibility, a better way of doing this is to define the interface that the model parameter must support. If the specific objects support derived interfaces (e.g. IDerivedModel : IModel) this will work too.
Look up a text-book on polymorphism.