隐式转换类型问题

本文关键字：问题 类型 转换 | 更新日期: 2023-09-27 18:05:53

我有以下类:

public class DictionaryBuilder<T> where T : IDictionary<string, object>, new()
{
    private List<Tuple<string, object>> values_ = new List<Tuple<string, object>>();
    public DictionaryBuilder<T> WithValue(string key, object obj)
    {
        values_.Add(Tuple.Create(key, obj));
        return this;
    }
    public static implicit operator T(DictionaryBuilder<T> builder)
    {
        return builder.Build();
    }
    public T Build()
    {
        var dict = new T();
        foreach (var value in values_)
        {
            dict.Add(value.Item1, value.Item2);
        }
        return dict;
    }
}
public static class Admin
{
    public static string IndexPath { get { return "Admin/Index"; } }
    public static DictionaryBuilder<RouteValueDictionary> IndexRoute 
    { 
        get 
        { 
            return new DictionaryBuilder<RouteValueDictionary>()
                .WithValue("controller", "Admin")
                .WithValue("action", "Index"); 
        } 
    }
}

它的用法是:

@Html.RouteLink("Admim",
    Admin.IndexRoute
        .WithValue("id",3),
    new DictionaryBuilder<Dictionary<string,object>>()
        .WithValue("class","AdminRouteLink")

这有点拗口，泛型对意图有一点阻碍。我想这样做:

public class RouteValues : DictionaryBuilder<RouteValueDictionary> { }
public class HtmlValues : DictionaryBuilder<Dictionary<string,object>> { }
public static class Admin
{
    public static string IndexPath { get { return "Admin/Index"; } }
    public static RouteValues IndexRoute 
    { 
        get 
        { 
            return new RouteValues()
                .WithValue("controller", "Admin")
                .WithValue("action", "Index"); 
        } 
    }
}
@Html.RouteLink("Admim",
    Admin.IndexRoute
        .WithValue("id",3),
    new HtmlValues()
        .WithValue("class","AdminRouteLink")

不幸的是，我得到一个转换错误，恐怕我不完全理解:

Cannot implicitly convert type  
'ControllerActionExporter
    .DictionaryBuilder<System.Web.Routing.RouteValueDictionary>'    
to 
'ControllerActionExporter.RouteValues'. 
An explicit conversion exists (are you missing a cast?)  

        return new RouteValues()
            .WithValue("controller", "Admin")
            .WithValue("action", "Index"); //error occurs on this line

我做错了什么，我如何纠正这个问题?

隐式转换类型问题

问题是WithValue返回DictionaryBuilder<T>，但IndexRoute属性返回更具体的类型RouteValues。尝试更改属性以返回DictionaryBuilder<T>:

public static DictionaryBuilder<RouteValueDictionary> IndexRoute 
{ 
    get 
    { 
        return new RouteValues()
            .WithValue("controller", "Admin")
            .WithValue("action", "Index"); 
    } 
}

另一种方法是为DictionaryBuilder<T>类创建一个泛型扩展方法，该方法返回与传入的类型相同的类型:

public static T WithValue(this T builder, string key, object obj)
{
        builder.WithValue(key, obj);
        return builder;
}
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