I'm making class library running on CLR .
I am wondering how I should code functions which return nullable type.
How can I make C++ ref class that works exactly same like the C# class below?
I searched on MSDN already, but i can't find anymore.
class ResultClass
{
}
class SomeClass
{
public ResultClass? getResult();
}
thank you for reading.
C++/CLI doesn't support the syntax sugar with the ? question mark, you have to use the Nullable<> struct explicitly. It otherwise has the same usage as C#, you never use Nullable<> on a reference type. Just return nullptr for a reference type like ResultClass. A snippet that shows syntax:
public ref class SomeClass {
public:
ResultClass^ getResult() {
return nullptr; // TODO: call native code
}
Nullable<int> nullableExample() {
Nullable<int> retval;
if (someCondition) retval = Nullable<int>(42);
return retval;
}
};
Related
I would like to use the nested Generics, like
class Class<List<T>> {
...
}
But always Dart Editor gives me alerts. How should I avoid these alerts?
Well, Dart Editor is right. This code doesn't make any sense. Without further information on what you are trying to do (don't hesitate to update your question), I am assuming you actually mean one of those:
class MyClass<T> {
List<T> listField;
// other stuff
}
Or maybe the list itself should be generic?
void main() {
MyClass<SomeCustomListClass<String>> instance = new MyClass();
}
class MyClass<T extends List<String>> {
T listField;
// ...
}
Or maybe everything has to be generic:
void main() {
MyClass<String, SomeCustomListClass<String>> instance = new MyClass();
}
class MyClass<TElement, TList extends List<TElement>> {
TList listField;
TElement _firstListElement;
// whatever that could be used for
}
I use int? for all my required 'FK' properties in ViewModels. This gives me an easy way of specifying on a Create view model that a value is nullable and must be assigned a value to satisfy the Required attribute.
My problem comes in because I create the domain model entity first, using a domain factory, then map it to the view model. Now, many of the nullable ints in the view model get assigned 0 from non-nullable ints in the domain model. I would prefer not to build the new entity in the view model and only map it back to the domain model to avoid his. What else can I do? i'm sure there is som Automapper voodoo that can help me.
EDIT: you dont need to do any of this, but i thought i'd leave it here for people looking for a similar solution. really all you have to do is just provide a mapping from int to int? like this: Mapper.Map<int, int?>()
in that case, I believe you could use a custom type converter, which inherits from automappers ITypeConverter. This code works, I've run it through .NET Fiddle:
using System;
using AutoMapper;
public class Program
{
public void Main()
{
CreateMappings();
var vm = Mapper.Map<MyThingWithInt, MyThingWithNullInt>(new MyThingWithInt());
if (vm.intProp.HasValue)
{
Console.WriteLine("Value is not NULL!");
}
else
{
Console.WriteLine("Value is NULL!");
}
}
public void CreateMappings()
{
Mapper.CreateMap<int, int?>().ConvertUsing(new ZeroToNullIntTypeConverter ());
Mapper.CreateMap<MyThingWithInt, MyThingWithNullInt>();
}
public class ZeroToNullIntTypeConverter : ITypeConverter<int, int?>
{
public int? Convert(ResolutionContext ctx)
{
if((int)ctx.SourceValue == 0)
{
return null;
}
else
{
return (int)ctx.SourceValue;
}
}
}
public class MyThingWithInt
{
public int intProp = 0;
}
public class MyThingWithNullInt
{
public int? intProp {get;set;}
}
}
You can always use the .ForMember() method on your mapping. Something like this:
Mapper
.CreateMap<Entity, EntityDto>()
.ForMember(
dest => dest.MyNullableIntProperty,
opt => opt.MapFrom(src => 0)
);
I have a command class that needs to have 2 constructors. However,
using structuremap it seems that I can only specify one constructor to
be used. I have solved the problem for now by subtyping the specific
command class, which each implementation implementing it's own
interface and constructor. Like the code below shows. The
ISelectCommand implements two separate interfaces for the
string constructor and the int constructor, just for the sake of
registering the two subtypes using structuremap.
However, I consider this a hack and I just wonder why is it not
possible for structuremap to resolve the constructor signature by the
type passed in as parameter for the constructor? Then I could register
the SelectProductCommand as an ISelectCommand and
instantiate it like:
ObjectFactury.With(10).Use>();
orObjectFactury.With("testproduct").Use>();
public class SelectProductCommand : ISelectCommand<IProduct>,
ICommand, IExecutable
{
private readonly Func<Product, Boolean> _selector;
private IEnumerable<IProduct> _resultList;
public SelectProductCommand(Func<Product, Boolean> selector)
{
_selector = selector;
}
public IEnumerable<IProduct> Result
{
get { return _resultList; }
}
public void Execute(GenFormDataContext context)
{
_resultList = GetProductRepository().Fetch(context,
_selector);
}
private Repository<IProduct, Product> GetProductRepository()
{
return ObjectFactory.GetInstance<Repository<IProduct,
Product>>();
}
}
public class SelectProductIntCommand: SelectProductCommand
{
public SelectProductIntCommand(Int32 id): base(x =>
x.ProductId == id) {}
}
public class SelectProductStringCommand: SelectProductCommand
{
public SelectProductStringCommand(String name): base(x =>
x.ProductName.Contains(name)) {}
}
P.s. I know how to tell structuremap what constructor map to use, but my again my question is if there is a way to have structuremap select the right constructor based on the parameter passed to the constructor (i.e. using regular method overloading).
The short answer is this post by the creator of Structuremap.
The long answer is regarding the structure you have in that piece of code. In my view, a command is by definition a "class" that does something to an "entity", i.e it modifies the class somehow. Think CreateNewProductCommand.
Here you are using commands for querying, if I'm not mistaken. You also have a bit of a separation of concern issue floating around here. The command posted defines what to do and how to do it, which is to much and you get that kind of Service location you're using in
private Repository<IProduct, Product> GetProductRepository()
{
return ObjectFactory.GetInstance<Repository<IProduct, Product>>();
}
The way I'd structure commands is to use CreateProductCommand as a data contract, i.e it only contains data such as product information.
Then you have a CreateProductCommandHandler which implements IHandles<CreateProductCommand> with a single method Handle or Execute. That way you get better separation of concern and testability.
As for the querying part, just use your repositores directly in your controller/presenter, alternatively use the Query Object pattern
I think I solved the problem using a small utility class. This class gets the concrete type from ObjectFactory and uses this type to construct the instance according to the parameters past into the factory method. Now on the 'client' side I use ObjectFactory to create an instance of CommandFactory. The implementation of CommandFactory is in another solution and thus the 'client solution' remains independent of the 'server' solution.
public class CommandFactory
{
public ICommand Create<T>()
{
return Create<T>(new object[] {});
}
public ICommand Create<T>(object arg1)
{
return Create<T>(new[] {arg1});
}
public ICommand Create<T>(object arg1, object arg2)
{
return Create<T>(new[] {arg1, arg2});
}
public ICommand Create<T>(object arg1, object arg2, object arg3)
{
return Create<T>(new[] {arg1, arg2, arg3});
}
public ICommand Create<T>(object[] arguments)
{
return (ICommand)Activator.CreateInstance(GetRegisteredType<T>(), arguments);
}
public static Type GetRegisteredType<T>()
{
return ObjectFactory.Model.DefaultTypeFor(typeof (T));
}
}
How to cast Java.Lang.Object to some native type?
Example:
ListView adapter contains instances of native type Message. When i am trying to get SelectedItem from ListView it returns instance of Message type casted to Java.Lang.Object, but I can't find solution to cast Java.Lang.Object back to Message.
var message = (Message)list.SelectedItem;
// throws Error 5 Cannot convert type 'Java.Lang.Object' to 'Message'
Please Help.
After long time debuging, have found the solution:
public static class ObjectTypeHelper
{
public static T Cast<T>(this Java.Lang.Object obj) where T : class
{
var propertyInfo = obj.GetType().GetProperty("Instance");
return propertyInfo == null ? null : propertyInfo.GetValue(obj, null) as T;
}
}
Usage example:
var message = list.GetItemAtPosition(e.Position).Cast<Message>();
bundle.PutInt("Message", message.ID);
After careful sdk study have found MonoDroid integrated extension for this purpose:
public static TResult JavaCast<TResult>(this Android.Runtime.IJavaObject instance)
where TResult : class, Android.Runtime.IJavaObject
Member of Android.Runtime.Extensions
The least magical way of getting a native type from the Spinner is to call
message = ((ArrayAdapter<Message>)list.Adapter).GetItem(list.SelectedItemPosition);
I used this code from above answer and it works fine to me
public static class ObjectTypeHelper
{
public static T Cast<T>(this Java.Lang.Object obj) where T : class
{
var propertyInfo = obj.GetType().GetProperty("Instance");
return propertyInfo == null ? null : propertyInfo.GetValue(obj, null) as T;
}
}
and this is how I used
var selectedLocation = locationSpinner.SelectedItem.Cast<Location>();
I am able to get my location object fine from spinner
For generic collections, the right answer would be to use JavaList, which is a Java.Lang.Object and also implements IList. But it involves more work that's for sure. This is actually just an adapter for Java's ArrayList implementation.
You could always try the JavaCast<> method (most of the views implement this)(not tested):
var message = list.SelectedItem.JavaCast< Message >();
If for some reason GetChildAtPosition is not possible, serialise the object to json string and then deserialise the string back to native class.
All of the above answers are correct but I found the simplest way for my case was to make the object a subclass of Java.Lang.Object.
For example I'm writing a Android app in Monotouch, mimicking the concept of a UITableView in iOS using the ExpandableListAdapter, which requires the equivalent of UITableViewCells, so I subclassed cell objects from Java.Lang.Object allowing me to implement a subclass of ExpandableListAdapter such as
public override Java.Lang.Object GetChild(int position, int childPosition)
Etc.
it's work for me:
public class HolderHelper<T> : Java.Lang.Object {
public readonly T Value;
public HolderHelper (T value)
{
this.Value = value;
}
}
test:
chkFileName.Tag = new HolderHelper<LinkInfo> (item);
LinkInfo link= (chkFileName.Tag as HolderHelper<LinkInfo>).Value;
I need some help in auto-registering generics using StructureMap. Here is my scenario:
public class Object<T>
{
}
public interface IBehvior<T>
{
void DoSomething(T t);
}
public class Behvior<T> : IBehvior<Object<T>>
{
public void DoSomething(Object<T> t)
{
}
}
What I want to accomplish is something like:
var x = ObjectFactory.GetInstance<IBehavior<Object<int>>();
But when I run this statement, it gives me an error that no default instance is configured. In my StructureMap configuration I've used
ConnectImplementationsToTypesClosing(typeof(IBehavior<>))
But it still doesn't work!
Note that this worked fine if I didn't have Object. For example, if I have:
public class IntBehavior : IBehavior<int>
{
}
Everything works perfectly fine. But when I replace int with a generic type, it doesn't work!
Any ideas?
Ok I discovered the solution here:
http://lostechies.com/jimmybogard/2010/01/07/advanced-structuremap-custom-registration-conventions-for-partially-closed-types/