C＃将通用委托传递给构造函数

Question

I'm new to C# and I try to find a way to pass a generic delegate to a constructor.

When calling a show endpoint, if there is pagination, the endpoint should return a Page instance. When creating the Page instance, the delegate method should be passed as one of constructor parameters. ShowsEndpoints will host many endpoints and many of these endpoints use pagination. I want to use only one class to handle all endpoints.

public partial class ShowsEndpoints : Endpoint
{
    public Func<Task<IEnumerable<object>>> FetchPopularShowsAsyncDelegate;
    public Func<Task<IEnumerable<object>>> FetchTrendingShowsAsyncDelegate;
    public Func<Task<IEnumerable<object>>> FetchMostWatchedShowsAsyncDelegate;

    public async Task<IEnumerable<object>> FetchPopularShowsAsync(int page = 1, int limit = 20)
    {
        return await SendAsync(new PopularShowsRequest(page, limit));
    }

    public async Task<IEnumerable<object>> FetchTrendingShowsAsync(int page = 1, int limit = 20)
    {
        return await SendAsync(new TrendingShowsRequest(page, limit));
    }

    public async Task<IEnumerable<object>> FetchMostWatchedShowsAsync(int page = 1, int limit = 20)
    {
        return await SendAsync(new MostWatchedShowsRequest(page, limit));
    }
}

Page class which will call the delegate to fetch the next page if there is a next page.

public class Page<TItem, TDelegate>
{
    private TDelegate _delegateCommand;

    public int CurrentPage { get; }
    public int TotalPages { get; }
    public int PageItemsCount { get; }
    public int TotalItemsCount { get; }
    public IEnumerable<TItem> Items { get; }

    public Page(int page, int totalPages, int itemsCount, int totalItemsCount, IEnumerable<TItem> items, TDelegate delegateCommand)
    {
        CurrentPage = page;
        TotalPages = totalPages;
        PageItemsCount = itemsCount;
        TotalItemsCount = totalItemsCount;
        Items = items;
        _delegateCommand = delegateCommand;
    }

    public bool HasNext()
    {
        return CurrentPage <= TotalPages;
    }

    public bool HasPrevious()
    {
        return CurrentPage >= 1;
    }

    public Page<TItem, TDelegate> Next()
    {
        // call _delegateCommand to fetch the next page items
    }

    public Page<TItem, TDelegate> Previous()
    {
        // call _delegateCommand to fetch the previous page items
    }
}

Is it possible ?

Thank you.

EDIT

I have updated my classes code in order to understand better my question. I have 3 endpoints associated with their delegates and I want the Page class to use any of these 3 delegates with the same code to avoid duplication. So _delegateCommand can be FetchPopularShowsAsyncDelegate , FetchTrendingShowsAsyncDelegate or FetchMostWatchedShowsAsyncDelegate .

Answer 1

I'm not sure if I've got the purpose of _delegateCommand right - I guess it should be the function returning IEnumerable<TItem> . If so, then you can declare it precisely like that, and then you won't have to introduce another generic parameter:

public class Page<TItem>
{
    private Func<IEnumerable<TItem>>_delegateCommand;

    public int CurrentPage { get; }
    public int TotalPages { get; }
    public int PageItemsCount { get; }
    public int TotalItemsCount { get; }
    public IEnumerable<TItem> Items { get; }

    public Page(int page, int totalPages, int itemsCount,
                int totalItemsCount, IEnumerable<TItem> items,
                Func<IEnumerable<TItem>> delegateCommand)
    {
        CurrentPage = page;
        TotalPages = totalPages;
        PageItemsCount = itemsCount;
        TotalItemsCount = totalItemsCount;
        Items = items;
        _delegateCommand = delegateCommand;
    }

    public bool HasNext()
    {
        return CurrentPage <= TotalPages;
    }

    public bool HasPrevious()
    {
        return CurrentPage >= 1;
    }
}