I'm having issues implementing an interface which vb.net is not picking it up through inheritance, not sure its possible but i believe there should be a way
Public Interface ITest
Sub SomeMethod()
End Interface
Public Class Test
Inherits OtherClass
Implements ITest
End Class
Public Class OtherClass
Sub SomeMethod()
End Sub
End Class
Class "OtherClass" is on another assembly where that ITest interface does not live and I cant have it there. However, with c# you are not forced to use the Implements keyword on each method, c# looks through the name and signatures.
So basically, Im getting the "Missing implementation of members" and what I was expecting was to be able to compile fine since Im inheriting a class that has the same methods defined on the interface.
Is this possible?
For OtherClass to implement the ITest interface, it needs a reference to that ITest interface.
Once you have it referenced, then your OtherClass would look like this:
Public Class OtherClass
Implements ITest
Sub SomeMethod() Implements ITest.SomeMethod
End Sub
End Class
Related
If I create a COM-visible VB.NET interface, such as:
<ComVisible(True)>
Public Interface IMyInterface
Sub MyMethod()
End Interface
Then the resulting type library will show IMyInterface inheriting IDispatch. Is there a way to inherit just IUnknown, and not IDispatch?
Use the InterfaceTypeAttribute Class like this:
<ComVisible(True), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)> _
Public Interface IMyInterface
Sub MyMethod()
End Interface
I need all my TableAdapters to implement a custom interface. The problem is that some of the members defined by the interface reside in the DataSet's designer file, which I don't want to (and shouldn't) alter, as that code will be regenerated automatically. I can't relocate those members to my code file either for the same reason. What's my way out of it?
When you implement an interface, the members you declare do not have to have the same names as the members of the interface and they don't have to be public. Let's say that you have this designer-generated class:
Partial Public Class SomeClass
Public Sub FirstMethod()
Console.WriteLine("FirstMethod")
End Sub
Public Sub SecondMethod()
Console.WriteLine("SecondMethod")
End Sub
End Class
and you want it to implement this interface:
Public Interface ISomeInterface
Sub FirstMethod()
Sub ThirdMethod()
End Interface
Notice that the interface has a method named FirstMethod but SomeClass already has a method named FirstMethod. You can add your own partial class to implement the interface like this:
Partial Public Class SomeClass
Implements ISomeInterface
Private Sub FirstMethodInternal() Implements ISomeInterface.FirstMethod
Me.FirstMethod()
End Sub
Public Sub ThirdMethod() Implements ISomeInterface.ThirdMethod
Console.WriteLine("ThirdMethod")
End Sub
End Class
The method that implements ISomeInterface.FirstMethod is not named FirstMethod so it doesn't clash with the existing method with that name and it is also Private so it cannot be accessed from outside using a reference of type SomeClass. Using a reference of type ISomeInterface is another matter though. If you use code like this:
Dim sc As ISomeInterface = New SomeClass
sc.FirstMethod()
sc.ThirdMethod()
you'll find that the FirstMethodInternal method of your SomeClass object gets invoked and, in turn, invokes the FirstMethod method of the same object. Try running that code and placing breakpoints on the FirstMethod and FirstMethodInternal methods to prove it to yourself.
Suppose I have piece of code like this:
Public Interface ISomething
....
End Interface
Public Class SomeClass
Implements ISomething
....
End Class
Now, if I inherit from SomeClass like this:
Public Class InheritedClass
Inherits SomeClass
....
End Class
will InheritedClass automatically implements ISomething, or must I use Implements ISomething in the InheritedClass' definition?
The interface was already implemented by the base class. Your derived class will thus implement it as well since it inherits the base class implementation. If you want to alter the base class implementation then you should declare the implementation method(s) virtual so you can override them.
Yes, the interface will be inherited as well.
This question already has answers here:
Partial Classes, LINQ, Interfaces and VB.NET
(2 answers)
Closed 2 years ago.
OK, I have to begin saying that I'm working with Visual Basic. The problem is that I have a Entity Framework object and I want to indicate that this object implements a interface, for example:
Public Interface ICatalog
Property created_at() As Date
Property id() As Long
End Interface
Those properties are allready in the object. In c# I've done this just by declaring a partial class of the object and indicates that implements that interface, but in basic is not working, I supouse that is because of the language sintaxis used to declare that a property is implementing some property of the interface, for example:
Public Property created_at() As Date Implements ICatalog.created_at
So is there any other way to accomplish this?
Take a look at this example.
Namespace MyAppDomain
Public Interface IFoo
Sub Bar()
End Interface
Public Interface IPerson
Function Gender() As String
End Interface
Public Class MyFooPerson : Implements IFoo, IPerson
Public Sub New()
End Sub
Public Sub Bar() Implements IFoo.Bar
End Sub
Public Function Gender() As String Implements IPerson.Gender
Return Nothing
End Function
End Class
End Namespace
You'll notice the MyFooPerson Class implements the IFoo Interface as well as the IPerson Interface. Each method then implements the corresponding Interface method.
Your example doesn't say whether or not the Class containing Public Property created_at() As Date Implements ICatalog.created_at is Implementing the ICatalog Interface.
What is the difference between a class with protected constructors and a class marked as MustInherit? (I'm programming in VB.Net but it probably equally applies to c#).
The reason I ask is because I have an abstract class that I want to convert the constructors to shared/static methods. (To add some constraints).
I can't do this because it's not possible to create an instance in the shared function.
I'm thinking to just remove the MustInherit keyword. Will this make any difference?
Thanks.
ETA:
I think i've answered my question, If I remove the MustInherit keyword, I can no longer include the MustOverrides, which are very useful.
With that in mind, is there any way around my problem?
ETA2:
To clarify, I can't do the below unless I remove the MustInherit keyword?
Public MustInherit MyBaseClass
Private Sub New()
End Sub
Protected Function CreateInstance(ParmList) As MyBaseClass
If ParmList is Ok Then Return New MyBaseClass()
End Function
End Class
You can call the Protected constructor using reflection and instantiate the class but you can't instantiate an abstract class in this way. You can declare MustOverride methods in MustInherit classes but Protected constructor can enforce nothing on derived classes.
You should always declare classes that are conceptually abstract as MustInherit. Protected constructors can be useful when you are providing it along with some Public overloads to provide some more functionality to derived classes.
If the class only has a protected constructor, it is still possible to have an instance of the class which can stand on its own. It would require working around the protected constructor, such as using reflection.
If the class is marked as MustInherit, it is impossible to have an instance of that class on its own. Instances can only be created of the derived/inherited classes.
Not really sure what you want.
If you need to create an object of the abstract class, I recommend you create a private class implementation of your abstract class and return it in your CreateInstanceMethod:
Public MustInherit MyBaseClass
Private BaseClassImplementation
Inherits MyBaseClass
...
End Class
Public Function CreateInstance(paramList) as MyBaseClass
If paramList Is Ok Then Return New BaseClassImplementation
End Function
End Class
However, if you want to add some constraints to the construction, I recommend to throw exceptions:
Public MustInherit MyBaseClass
Protected Sub New(paramList)
If paramList IsNot Ok Then Thow New Exception
...
End Sub
End Class