I'm trying to implement generic interface method but keep getting an error. I'm pasting the code to better explain what I want to do.
What I'm trying to achieve is: based on some input data (SomeModelA, SomeModelB) I want to get the same return type (Template).
namespace GenericInterfacePuzzle
{
class Program
{
static void Main(string[] args)
{
var workerA = new WorkerA();
var itemsBasedOnModelA = workerA.Get(new List<SomeModelA>());
var workerB = new WorkerB();
var itemsBasedOnModelB = workerB.Get(new List<SomeModelB>());
}
}
public interface IWorker
{
Template Get<T>(List<T> someModels);
}
public class WorkerA : IWorker
{
public Template Get<SomeModelA>(List<SomeModelA> someModels)
{
ProcessModels(someModels);
return new Template(); // let's say it's based on the result of ProcessModels
}
private void ProcessModels(List<SomeModelA> models)
{
var x = models.First();
}
}
public class WorkerB : IWorker
{
public Template Get<SomeModelB>(List<SomeModelB> someModels)
{
ProcessModels(someModels);
return new Template(); // let's say it's based on the result of ProcessModels
}
private void ProcessModels(List<SomeModelB> models)
{
var x = models.First();
}
}
public class SomeModelA
{
public string Name { get; set; }
}
public class SomeModelB
{
public string Age { get; set; }
}
public class Template
{
// Irrevelant return type
}
}
I want to know at the level of WorkerA/WorkerB class that I'm dealing with a concrete model, and based on that I want to return a Template class instance
The problem is that in the lines that call Process:
ProcessModels(someModels);
I get an error saying:
Error CS1503 Argument 1: cannot convert from 'System.Collections.Generic.List of SomeModelA' to 'System.Collections.Generic.List of GenericInterfacePuzzle.SomeModelA'
Any feedback appreciated what might be going wrong here, and why doesn't it recognize the model classes when passed to the functions.
Chris
1) You need to define the generic parameter on the level of your interface. Otherwise the T parameter is not known to the compiler:
public interface IWorker<T> where T: SomeModel
{
Template Get(List<T> someModels);
}
2) you need to make a constraint since you probably don't want any type to be given to your interface. It would be preferable to make a baseclass for your models and let them inherit from it:
public abstract class SomeModel { ... }
public class SomeModelA : SomeModel
{
public string Name { get; set; }
}
public class SomeModelB : SomeModel
{
public string Age { get; set; }
}
This way it will allow you to specify the model directly in the declaration of the class which will implement the interface (see point 3)
3) Now you need to specify in the child classes which model belongs to which workertype:
public class WorkerA : IWorker<SomeModelA>
{
public Template Get(List<SomeModelA> someModels)
{
ProcessModels(someModels);
return new Template(); // let's say it's based on the result of ProcessModels
}
private void ProcessModels(List<SomeModelA> models)
{
var x = models.First();
}
}
public class WorkerB : IWorker<SomeModelB>
{
public Template Get(List<SomeModelB> someModels)
{
ProcessModels(someModels);
return new Template(); // let's say it's based on the result of ProcessModels
}
private void ProcessModels(List<SomeModelB> models)
{
var x = models.First();
}
}
You also should remove the generic specification in your Get method!
public Template Get<SomeModelA>(List<SomeModelA> someModels)
^
|
remove this
this is already specified when you implement the interface:
public class WorkerA : IWorker<SomeModelA>
4) and the last thing is you test in the main method:
var worker = new WorkerA();
var itemsBasedOnModelA = worker.Get(new List<SomeModelA>());
var workerB = new WorkerB();
var itemsBasedOnModelB = worker.Get(new List<SomeModelB>());
^
|
this should be [workerB]!
Related
I am looking for a way to support multi level of inheritance for generic type constraint.
Common generic interface
public interface ICommon<T>
{
T OrignalData {get;set;}
string ChangeJson {get;set;}
T Merged {get;set;}
void Inject();
}
Common base class implements ICommon
public class Base <T>: ICommon<T>
{
public T OrignalData {get;private set;}
public string ChangeJson {get;set;}
public T Merged {get;private set;}
public void Inject(T orignal)
{
if (orignal == null)
return;
var settings = new JsonSerializerSettings
{
ObjectCreationHandling = ObjectCreationHandling.Auto
};
dynamic merged = orignal.Clone();
JsonConvert.PopulateObject(this.ChangeJson, merged, settings);
this.Merged = merged;
this.Orignal = orignal;
}
}
Department class inherits Base class
public class Deparment : Base<Deparment>
{
}
OrgnizationDepartment class inherits Deparment
public class OrgnizationDepartment : Deparment
{
}
class View expect ICommon must implement on passed calls
public class View<T> where T : ICommon<T>
{
//This class is totally dynamic to visualize any json data along with old and new value of requested json for any class like department or org..
}
Test
public class Test
{
public void TestConstraint()
{
//No error
var deptView = new View<Deparment>();
//Error as Base not directly implemented on OrgnizationDepartment
var orgView = new View<OrgnizationDepartment>();
}
}
how do I define my constraint that should support for multi level as well.
One way out of this would be "composition over inheritance".
Here is a naive example, that is still relatively close to your code:
using System;
using Newtonsoft.Json;
public class Program
{
public static void Main()
{
//No error
var deptView = new View<Deparment>();
//Formerly Error
var orgView = new View<OrgnizationDepartment>();
}
}
public interface ICommon<T> where T : ICloneable
{
// returns a tuple
(T,T,string) Inject(T original, string change);
}
public class Base <T>: ICommon<T> where T : ICloneable
{
// we can reuse this...
private readonly JsonSerializerSettings settings = new JsonSerializerSettings
{
ObjectCreationHandling = ObjectCreationHandling.Auto
};
public (T,T,string) Inject(T original, string change)
{
if (original is null)
return default;
// this forces T to implement ICloneable ... just saying...
dynamic merged = original.Clone();
JsonConvert.PopulateObject(change, merged, settings);
return (original, merged, change);
}
}
public class Deparment : ICloneable, ICommon<Deparment>
{
// could also be created in ctor. Maybe use Ctor injection.
private readonly Base<Deparment> common = new Base<Deparment>();
public object Clone(){return this;} // this is of course nonsense. Clone properly! I did this to avoid dotnetfiddle screaming at me.
public (Deparment, Deparment, string) Inject(Deparment original, string change){
return common.Inject(original, change);
}
}
public class OrgnizationDepartment : ICloneable, ICommon<OrgnizationDepartment>
{
private readonly Base<OrgnizationDepartment> common = new Base<OrgnizationDepartment>();
public object Clone() {return this;}
public (OrgnizationDepartment, OrgnizationDepartment, string) Inject(OrgnizationDepartment original, string change){
return common.Inject(original, change);
}
}
Here is my generic method from which i want to return the class object
public class TestBase
{
public T NavigateandReturntheObject<T>() where T : new()
{
//do navigate to page stuff and return the page object
//previously it was - return new T();
//Now i want to do something like this
return PageObjectBase<T>.PageObject;
}
}
Above method calling the below static generic class which will handle object creation of a particular class
public static class PageObjectBase<T> where T : class, new()
{
private static T singleTonObject;
public static T PageObject
{
get
{
return InstanceCreation();
}
}
public static T InstanceCreation()
{
if (singleTonObject == null)
{
singleTonObject = new T();
}
return singleTonObject;
}
}
How can i call the PageObject property from my test base class please advice.
Note : I have searched forum and find answers relevant to generic method to another generic method calling.The same is achieved by reflection.Can we use reflection in my case too? If so how can we do it.
You can add another constraint 'class' to NavigateandReturntheObject
public T NavigateandReturntheObject<T>() where T : class,new()
Complete Code.
public class TestBase
{
public T NavigateandReturntheObject<T>() where T : class,new()
{
//do navigate to page stuff and return the page object
//previously it was - return new T();
//Now i want to do something like this
return PageObjectBase<T>.PageObject;
}
}
Demo Code
public class TestClass
{
public string Name{get;set;}
public TestClass()
{
Name = "Dummy Name";
}
}
var testBase = new TestBase();
var sample = testBase.NavigateandReturntheObject<TestClass>();
Console.WriteLine(sample.Name);
Output
Dummy Name
I have the following data class and VM class:
public interface IData
{
string Name
{
get;
}
}
public class DataPartial: IData
{
public DataPartial()
{
}
public string Name => "Data partial";
}
public class DataFull : IData
{
public string Name => "Data full";
public DataFull()
{
}
}
public interface IVM
{
IData Data { get; }
}
public interface IVM_partial: IVM
{
new DataPartial Data { get; }
}
public class VM_Partial : IVM_partial
{
public VM_Partial()
{
Data = new DataPartial();
}
public DataPartial Data { get; set; }
IData IVM.Data => Data;
}
public interface IVM_Total:IVM_partial
{
new DataFull Data { get; }
}
public class VM_Total : IVM_Total
{
public VM_Total(IVM_partial dataA)
{
Data = new DataFull();
DataA_interface = dataA;
}
public IVM_partial DataA_interface { get; }
public DataFull Data { get; private set; }
DataPartial IVM_partial.Data => DataA_interface.Data;
IData IVM.Data => Data;
}
public static class RunVM<T, VM>
where T: class, IData
where VM :class, IVM
{
public static T RunMe(VM hi)
{
var vmA = (hi as VM); //how to force-cast this to the VM type??!!
return (T)vmA.Data;
}
}
class Program
{
static void Main(string[] args)
{
VM_Partial partialData = new VM_Partial();
var VMClass = new VM_Total(partialData);
RunVM<DataFull, IVM_Total>.RunMe(VMClass);
RunVM<DataPartial, IVM_partial>.RunMe(VMClass); //here it throws exception because I can't force cast the IVM to IVM_partial
}
}
At the method RunVM<DataPartial, IVM_partial>.RunMe(VMClass);, I want it to return me the DataPartial object, which I know it's there in the object VMClass, but I cannot get it done.
I will get an InvalidCastException when I am at the RunMe method, because the parameter hi is always VMClass, and I can never get it to behave like IVM_partial class. In other words, I can't cast hi to a more basic interface IVM_partial.
How to cast hi to a more basic interface IVM_partial? Is it possible at all, and if not, why not?
It's not the cast that's the problem - it's that you expect the compiler (or runtime) to pick up on the fact that the cast is to a type that declares a new Data property.
This line in RunMe:
return (T)vmA.Data;
... will always use the Data property declared by IVM, because that's the only property the compiler knows about when it's compiling that method. It doesn't matter that you're casting to another interface that contains a new Data property... the cast is about an execution-time check; it doesn't change which Data property the method uses.
It's unclear to me exactly what you're trying to achieve here, but I strongly suspect that you'll need to change tack significantly - maybe by adding another generic type parameter into the mix, maybe by using polymorphism more, or maybe changing the design more radically.
I have the following code:
public interface IMyActionFactory
{
AbstractAction<T> CreateAction<T>(MyActionParamBase paramBase = null)
where T : MyActionParamBase;
}
public sealed class MergeActionParam : MyActionParamBase
{
}
public class MergeTest
{
private readonly IMyActionFactory _actionFactory = new DefaultMyActionFactory();
[Theory]
[PropertyData("MergeWorksData")]
public void MergeWorks(/*params here*/)
{
var param = new MergeActionParam();
// populate param here
var sut = _actionFactory.CreateAction<MergeActionParam>(param);
sut.DoAction();
}
}
I am getting an error
"..Error 10 Using the generic type 'IMyActionFactory' requires 1
type arguments..."
Why does the compiler expect a type to be passed to my IMyActionFactory, since I have declared the interface without a T? As far as the method is concerned its the only one to expect the type. Am I missing something here?
How can I make it work without redefining the interface signature?
EDIT:
Feeling a bit embarassed here, because the quick code I put down and ran seperately in a standalone online c# compiler doesnt give any compilation errors. However, going back to my original solution (tens of projects altogether) the error is still there.. Maybe has something to do with the XUnit ?..not sure
public interface IMyActionFactory
{
AbstractAction<T> CreateAction<T>(MyActionParamBase paramBase = null)
where T : MyActionParamBase;
}
public interface IAction
{
void DoAction();
}
public abstract class AbstractAction<T> : IAction
where T : MyActionParamBase
{
public void DoAction()
{
}
}
public class MyActionParamBase
{
public MyActionParamBase()
{
}
}
public sealed class MergeActionParam : MyActionParamBase
{
}
public class DefaultMyActionFactory : IMyActionFactory
{
public AbstractAction<T> CreateAction<T>(MyActionParamBase paramBase = null) where T : MyActionParamBase
{
return null;
}
}
public class MergeTest
{
private readonly IMyActionFactory _actionFactory = new DefaultMyActionFactory();
public void MergeWorks(/*params here*/)
{
var param = new MergeActionParam();
// populate param here
var sut = _actionFactory.CreateAction<MergeActionParam>(param);
sut.DoAction();
}
}
I need to have a wrapper class that exposes some properties of my entity class called ProfileEntity.
I tried doing it by deriving from this entity and then creating properties that return specific entity properties, but it says I cannot cast from ProfileEntity to ProfileEntityWrapper.
When I try to put the return values of a method that returns a 'ProfileEntity' into the wrapper I get the above error.
How do I create such a wrapper class that is castable?
Example
class ProfileEntityWrapper : ProfileEntity
{
public string Name
{
get
{
return this.ProfileEntityName;
}
}
}
public class Someclass
{
public ProfileEntity SomeMethod()
{
return ProfileEntity; // example of method returning this object
}
}
public class SomeOtherlClass
{
SomeClass sc = new SomeClass();
public void DoSomething()
{
ProfileEntityWrapper ew = (ProfileEntityWrapper)sc.SomeMethod(); // Cannot do this cast!!!
}
}
You cannot cast an object of ProfileEntity to ProfileEntityWrapper.
var entity = new ProfileEntity(); // this object is only of type ProfileEntity
var wrapper = new ProfileEntityWrapper(); // this object can be used as both ProfileEntityWrapper and ProfileEntity
You probably want to return a ProfileEntityWrapper in SomeMethod():
public class Someclass
{
public ProfileEntity SomeMethod()
{
return new ProfileEntityWrapper(); // it's legal to return a ProfileEntity
}
}
No, that is not possible.
To accomplish this problem you can maybe try this one:
public class ProfileEntity
{
public string ProfileEntityName { get; set; }
}
public class ProfileEntityWrapper
{
public ProfileEntityWrapper(ProfileEntity entity)
{
Entity = entity;
}
public ProfileEntity Entity { get; private set; }
public string Name
{
get
{
return Entity.ProfileEntityName;
}
}
}
public class SomeClass
{
public ProfileEntity SomeMethod()
{
// example of method returning this object
ProfileEntity temp = new ProfileEntity();
return temp;
}
}
public class SomeOtherClass
{
SomeClass sc = new SomeClass();
public void DoSomething()
{
//Create a new Wrapper for an existing Entity
ProfileEntityWrapper ew = new ProfileEntityWrapper(sc.SomeMethod());
}
}
If you are allowed to edit the ProfileEntity class, or if the ProfileEntity class is a generated partial class, you could add an interface instead of using a wrapper. You wouldn't need to do any casting with an interface either. Example:
public interface IProfile
{
string Name { get; }
}
public partial class ProfileEntity : IProfile
{
public string Name
{
get
{
return this.ProfileEntityName;
}
}
}
public class SomeClass
{
public ProfileEntity SomeMethod()
{
return ProfileEntity;
}
}
public class SomeOtherClass
{
SomeClass sc = new SomeClass();
public void DoSomething()
{
IProfile ew = sc.SomeMethod();
}
}
The IProfile instance will only provide access to the Name property.
This's no correct code from polymorphism aspect.
If we will take the famous polymorphism example when there're base Shape class and Circle, Polygon and Rectangle classes that extend the Shape class, your code will try to cast some shape into circle and as you understand this's invalid casting operation.
So to make this code work you must be sure that SomeClass.SomeMethod() will return instance of ProfileEntityWrapper or perform type check before the casting, like this:
ProfileEntity temp = sc.SomeMethod();
if(temp is ProfileEntityWrapper)
ProfileEntityWrapper ew = (ProfileEntityWrapper) temp;