CODEWITHSUNDEEP
c#interfaceasp.net-core-2.0
Yobikir
Yobikir

Reputation: 119

implement multiple functions of Interfaces with returns which inherit from one another

So, I have 2 base interfaces. For example:

public interface IPageParameter
{
    int Pagenumber { get; set; }
}
public interface IPageModel
{
    int CurrentPage { get; set; }

    IPageParameter GetLinkParameter();
}

now I want to extent them, without changing them, so I write two new Interfaces:

public interface IPageParameterExt : IPageParameter
{
    int PerPage { get; set; }
}
public interface IPageModelExt : IPageModel
{
    int CurrentPerPage { get; set; }

    new IPageParameterExt GetLinkParameter();
}

now if I implement this in a class I need to write both functions out

public class DefaultPageParameterExt : IPageParameterExt
{
    public int Pagenumber { get; set; }
    public int PerPage { get; set; }
}

public class PageModel : IPageModelExt
{
    public int CurrentPage { get; set; }
    public int CurrentPerPage { get; set; }


    IPageParameterExt IPageModelExt.GetLinkParameter()
    {
        return new DefaultPageParameterExt()
        {
            Pagenumber = CurrentPage,
            PerPage = CurrentPerPage
        };
    }

    IPageParameter IPageModel.GetLinkParameter()
    {
        return ((IPageModelExt)this).GetLinkParameter();
    }
}

But that doesn't seem very good to me. I mean, if it extends further, does that mean that each time there have to be written another GetLinkParameter? Or is there a way to tell an interface that this function can be used for the function of its Parent? Or tell the class that you can use this function as well for the implementation for both functions?

EDIT: Okay, because a question here is what I want to do with the given Example (which is the simplest time I need this, but I need it in similar Terms for a few other Tasks):

I currently work with ASP Core 2.0.5 Razorpages and have implemented multiple IHtmlHelper extensions, there the Pagemodels have implement the IPageModel to be able to create some simple paging of elements. The IPageParameter contains what is needed to create a Hyperlink with changed Parameters (eg Pagenumber = 1 for first Page or Pagenumber += 1 for next Page).

Now my Job is it to create an IHtmlHelper-extension which allows it to choose how many Elements on Each Page are displayed, instead of using a fixed Value.

EDIT2:

Here some simplified code for a Extension since it was requested.

public static IHtmlContent GetPageButtons<TModel>(this IHtmlHelper<TModel> helper, TModel Model)
        where TModel : IPageModel
{
    var urlHelper = new UrlHelper(helper.ViewContext);
    var html = new HtmlContentBuilder();
    var para = Model.GetLinkParameter();

    string prevclass = Model.CurrentPage <= 1 ? "btn btn-default disabled" : "btn btn-default";

    html.AppendHtml(@"<table style=""width:1%"">")
            .AppendHtml("<tr>")
                .AppendHtml("<td>");

    /*other buttons*/

    para.Pagenumber = Model.CurrentPage -1;

    html
                    .AppendFormat(@"<a href=""{1}"" class=""{0}"">{2}</a>", prevclass, urlHelper.Action("", para), "<")
                .AppendHtml("</td>")

    /*other buttons*/

            .AppendHtml("</tr>")
        .AppendHtml("</table>");

    return html;
}

Upvotes: 0

Views: 594

Answers (1)

MakePeaceGreatAgain
MakePeaceGreatAgain

Reputation: 37050

Thas a good deal for generics. Instead of writing new extensions for every possible type, simply use a single method for all possible types. Then you don´t even need any extending interface:

public interface IPageModel<T>
{
    int CurrentPage { get; set; }    
    T GetLinkParameter<T>();
}

public class PageModel : IPageModel<IMyInterface>
{
    public int CurrentPage { get; set; }

    IMyInterface GetLinkParameter()
    {
        return new DefaultPageParameterExt()
        {
            Pagenumber = CurrentPage,
            PerPage = CurrentPerPage
        };
    }
}

Upvotes: 1

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