Question on interfaces and inheritance

Should a class implementing an interface define the methods in the
interface?
That seems logical to me but I have the following code:

public class XmlDataSourceMarc : XmlDataSource
{
protected DataSourceView tst;
public override DataSourceView GetView(string viewName)
{
return tst;
}
}

This gives the error: 'XmlDataSourceMarc.GetView(string)': no suitable
method found to override


Now if I look at the base class, it's true GetView is not defined in the
class

public class XmlDataSource : HierarchicalDataSourceControl, IDataSource,
IListSource
{
public XmlDataSource();
public virtual int CacheDuration { get; set; }
public virtual DataSourceCacheExpiry CacheExpirationPolicy { get;
set; }
public virtual string CacheKeyDependency { get; set; }
public virtual string Data { get; set; }
public virtual string DataFile { get; set; }
public virtual bool EnableCaching { get; set; }
public virtual string Transform { get; set; }
public virtual XsltArgumentList TransformArgumentList { get; set; }
public virtual string TransformFile { get; set; }
public virtual string XPath { get; set; }
public event EventHandler Transforming;
protected override HierarchicalDataSourceView
GetHierarchicalView(string viewPath);
public XmlDocument GetXmlDocument();
protected virtual void OnTransforming(EventArgs e);
public void Save();
}

But the IDataSource interface it should implement has.

public interface IDataSource
{
event EventHandler DataSourceChanged;
DataSourceView GetView(string viewName);
ICollection GetViewNames();
}

So what am I missing? Why XmlDataSource does not have an implementation of
DataSourceView GetView(string viewName) while it implements the interface
IDataSource that defines it?

Marc Wentink

Marc brought next idea :
> Should a class implementing an interface define the methods in the interface?
> That seems logical to me but I have the following code:
>
> public class XmlDataSourceMarc : XmlDataSource
> {
> protected DataSourceView tst;
> public override DataSourceView GetView(string viewName)
> {
> return tst;
> }
> }
>
> This gives the error: 'XmlDataSourceMarc.GetView(string)': no suitable
> method found to override
>
>
> Now if I look at the base class, it's true GetView is not defined in the
> class
>
> public class XmlDataSource : HierarchicalDataSourceControl, IDataSource,
> IListSource
> {
> public XmlDataSource();
> public virtual int CacheDuration { get; set; }
> public virtual DataSourceCacheExpiry CacheExpirationPolicy { get;
> set; }
> public virtual string CacheKeyDependency { get; set; }
> public virtual string Data { get; set; }
> public virtual string DataFile { get; set; }
> public virtual bool EnableCaching { get; set; }
> public virtual string Transform { get; set; }
> public virtual XsltArgumentList TransformArgumentList { get; set; }
> public virtual string TransformFile { get; set; }
> public virtual string XPath { get; set; }
> public event EventHandler Transforming;
> protected override HierarchicalDataSourceView
> GetHierarchicalView(string viewPath);
> public XmlDocument GetXmlDocument();
> protected virtual void OnTransforming(EventArgs e);
> public void Save();
> }
>
> But the IDataSource interface it should implement has.
>
> public interface IDataSource
> {
> event EventHandler DataSourceChanged;
> DataSourceView GetView(string viewName);
> ICollection GetViewNames();
> }
>
> So what am I missing? Why XmlDataSource does not have an implementation of
> DataSourceView GetView(string viewName) while it implements the interface
> IDataSource that defines it?
>
> Marc Wentink

The method does exist but is defined as "explicit interface
implementation". If you cast the XmlDataSource to IDataSource, then you
can use the GetView method.

Hans Kesting

If I look at XmlDataSource with Reflector, it does have an implementation of
GetView.

"Marc" <m.wentink5@removethischello.nl> wrote in message
news:%23tweqIFCJHA.4884@TK2MSFTNGP02.phx.gbl...
> Should a class implementing an interface define the methods in the
> interface?
> That seems logical to me but I have the following code:
>
> public class XmlDataSourceMarc : XmlDataSource
> {
> protected DataSourceView tst;
> public override DataSourceView GetView(string viewName)
> {
> return tst;
> }
> }
>
> This gives the error: 'XmlDataSourceMarc.GetView(string)': no suitable
> method found to override
>
>
> Now if I look at the base class, it's true GetView is not defined in the
> class
>
> public class XmlDataSource : HierarchicalDataSourceControl,
> IDataSource, IListSource
> {
> public XmlDataSource();
> public virtual int CacheDuration { get; set; }
> public virtual DataSourceCacheExpiry CacheExpirationPolicy { get;
> set; }
> public virtual string CacheKeyDependency { get; set; }
> public virtual string Data { get; set; }
> public virtual string DataFile { get; set; }
> public virtual bool EnableCaching { get; set; }
> public virtual string Transform { get; set; }
> public virtual XsltArgumentList TransformArgumentList { get; set; }
> public virtual string TransformFile { get; set; }
> public virtual string XPath { get; set; }
> public event EventHandler Transforming;
> protected override HierarchicalDataSourceView
> GetHierarchicalView(string viewPath);
> public XmlDocument GetXmlDocument();
> protected virtual void OnTransforming(EventArgs e);
> public void Save();
> }
>
> But the IDataSource interface it should implement has.
>
> public interface IDataSource
> {
> event EventHandler DataSourceChanged;
> DataSourceView GetView(string viewName);
> ICollection GetViewNames();
> }
>
> So what am I missing? Why XmlDataSource does not have an implementation of
> DataSourceView GetView(string viewName) while it implements the interface
> IDataSource that defines it?
>
> Marc Wentink
>
>

"Hans Kesting" <news.hansdk@spamgourmet.com> wrote

> The method does exist but is defined as "explicit interface
> implementation".

Aha. I will do some reading on that! Thanks.

"Hans Kesting" <news.hansdk@spamgourmet.com> wrote


> The method does exist but is defined as "explicit interface
> implementation". If you cast the XmlDataSource to IDataSource, then you
> can use the GetView method.

But let us say I do not want to use the GetView method, as a method of a
instantated variable of type XmlDataSource , but I want to define a new
subclass of XmlDataSource that overrides the GetView method? How do I do
that?

public class XmlDataSourceMarc : XmlDataSource /* fails */
/*
HierarchicalDataSourceControl fails */
/* DataSourceControl
works */
{
DataSourceView myView;
protected override DataSourceView GetView(string viewName)
{
return myView;
}
}

On Wed, 27 Aug 2008 09:18:39 -0700, Marc <m.wentink5@removethischello.nl>
wrote:

> "Hans Kesting" <news.hansdk@spamgourmet.com> wrote
>
>
>> The method does exist but is defined as "explicit interface
>> implementation". If you cast the XmlDataSource to IDataSource, then you
>> can use the GetView method.
>
> But let us say I do not want to use the GetView method, as a method of a
> instantated variable of type XmlDataSource , but I want to define a new
> subclass of XmlDataSource that overrides the GetView method? How do I do
> that?

You need to declare your sub-class as also implementing the interface, and
then explicitly implement your override:

public class XmlDataSourceMarc : XmlDataSource, IDataSource
{
protected DataSourceView tst;
public DataSourceView IDataSource.GetView(string viewName)
{
return tst;
}
}

Pete

"Peter Duniho" <NpOeStPeAdM@nnowslpianmk.com> wrote

> You need to declare your sub-class as also implementing the interface, and
> then explicitly implement your override:
>
> public class XmlDataSourceMarc : XmlDataSource, IDataSource
> {
> protected DataSourceView tst;
> public DataSourceView IDataSource.GetView(string viewName)
> {
> return tst;
> }
> }


Ok, now I am reallly starting to feel stupid but I got this and it still
gives an error.

using System;
using System.Data;
using System.Configuration;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;

public class XmlDataSourceMarc : XmlDataSource, IDataSource
{
DataSourceView myView;
public override DataSourceView GetView(string viewName)
{
return myView;
}
}

Error 1 'XmlDataSourceMarc.GetView(string)': no suitable method found to
override E:\user\m.wentink\My Documents\Visual Studio
2008\H4SPXML1\App_Code\XmlDataSourceMarc.cs 16 36 E:\...\H4SPXML1\

I tried to change public in protected but that's not it either.

And here some link with information about GetView

http://msdn.microsoft.com/en-us/libr...ew(VS.85).aspx

Marc brought next idea :
> "Peter Duniho" <NpOeStPeAdM@nnowslpianmk.com> wrote
>
>> You need to declare your sub-class as also implementing the interface, and
>> then explicitly implement your override:
>>
>> public class XmlDataSourceMarc : XmlDataSource, IDataSource
>> {
>> protected DataSourceView tst;
>> public DataSourceView IDataSource.GetView(string viewName)
>> {
>> return tst;
>> }
>> }
>
>
> Ok, now I am reallly starting to feel stupid but I got this and it still
> gives an error.
>
> using System;
> using System.Data;
> using System.Configuration;
> using System.Linq;
> using System.Web;
> using System.Web.Security;
> using System.Web.UI;
> using System.Web.UI.WebControls;
>
> public class XmlDataSourceMarc : XmlDataSource, IDataSource
> {
> DataSourceView myView;
> public override DataSourceView GetView(string viewName)
> {
> return myView;
> }
> }
>
> Error 1 'XmlDataSourceMarc.GetView(string)': no suitable method found to
> override E:\user\m.wentink\My Documents\Visual Studio
> 2008\H4SPXML1\App_Code\XmlDataSourceMarc.cs 16 36 E:\...\H4SPXML1\
>
> I tried to change public in protected but that's not it either.
>
> And here some link with information about GetView
>
> http://msdn.microsoft.com/en-us/libr...ew(VS.85).aspx

You missed something on the methodname: it's "IDataSource.GetView"
(note the extra "IDataSource" that signals this is an explicit
interface implementation.

Hans Kesting

"Hans Kesting" <news.hansdk@spamgourmet.com> wrote


> You missed something on the methodname: it's "IDataSource.GetView" (note
> the extra "IDataSource" that signals this is an explicit interface
> implementation.

public class XmlDataSourceMarc : XmlDataSource, IDataSource
{
DataSourceView myView;
DataSourceView IDataSource.GetView(string viewName)
{
return myView;
}
}

Ok this works and I will do some study on interface semantics, and write
some C# code on it. But thanks for the help on my probably newbee questions.