如何使返回不同类型但接受相同类型实例的方法/ s 通用？

Question

我有多种从 XML 读取数据的方法，格式如下：

<?xml version = "1.0" encoding="UTF-8" standalone="yes"?>
<document>
    <employee>
        <name>
            <lastname>Sample</lastname>
            <firstname>Test</firstname>
        </name>
        <professionalDetails>
            <hiredate>October 15, 2016</hiredate>
            <designation>Clerk</designation>
        </professionalDetails>
        <projects>
            <project>
                <product>Printer</product>
                <id>111</id>
                <price>$111.00</price>
            </project>
            <project>
                <product>Laptop</product>
                <id>222</id>
                <price>$989.00</price>
            </project>
        </projects>
    </employee>
</document>

要读取上述数据，我有以下方法及其各自的类。

• 请注意，我有自己的“GetElementAsString”方法实现。请原谅我没有提供实现。

方法：

    private static NameDetails GetsNameDetails(XNode content)
    {
        var element = content.XPathSelectElement("document/employee/name");

        return new NameDetails
        {
            FirstName = element.GetElementAsString("firstName"),
            LastName = element.GetElementAsString("lastName")
        };
    }

    private static ProfessionalDetails GetsProfessionalDetailsDetails(XNode content)
    {
        var element = content.XPathSelectElement("document/employee/professionalDetails");

        return new ProfessionalDetails
        {
            HireDate = element.GetElementAsString("hiredate"),
            Designation = element.GetElementAsString("designation")
        };
    }

    private static Projects GetsProjectDetails(XNode content)
    {
        var element = content.XPathSelectElement("document/employee/projects/project");

        return new Projects
        {
            Id = element.GetElementAsString("id"),
            Price = element.GetElementAsString("price"),
            Product = element.GetElementAsString("product")
        };
    }
}

internal class Projects
{
    public int Id { get; set; }
    public string Product { get; set; }
    public string Price { get; set; }
}

internal class ProfessionalDetails
{
    public DateTime HireDate { get; set; }
    public string Designation { get; set; }
}

internal class NameDetails
{
    public string FirstName  { get; set; }
    public string LastName { get; set; }
}

两种方法的基本逻辑相同。初始化类型是唯一改变的东西。方法的返回值和要初始化的属性/字段发生变化，但参数保持不变。

我如何为以下方法使用一个通用方法并决定在运行时初始化的类型？

Answer 1

您可以添加一个泛型类型，然后根据类型决定您要如何解析节点：

private static T GetsDetails<T>(XNode content)
{
    if(typeof(T) == typeof(ProjectDetails)){
        var element = content.XPathSelectElement("document/employee/projects/project");

        return (T)new Projects
        {
            Id = element.GetElementAsString("id"),
            Price = element.GetElementAsString("price"),
            Product = element.GetElementAsString("product")
        };
    }
    else if(typeof(T) == typeof(ProfessionalDetails){ ... } 
    else if (...) {...}
}

不过，我不推荐这种方法：您仍然需要进行类型检查，而且收获很少。您的初始实现要简单得多。

Answer 2

你可以这样写：

private static T ThingFiller<T>(
    XNode context, 
    string elementStr,
    params Action<Func<string, string>, T>[] setters
)
    where T : new()
{
    var element = context.XPathSelectElement(elementStr);
    var t = new T();

    foreach (var setter in setters)
        setter(element.GetElementAsString, t);      

    return t;
}

private static NameDetails GetsNameDetails(XNode content)
{
    return ThingFiller<NameDetails>(content, "document/employee/name",
        (func, nd) => nd.FirstName = func("firstName"),
        (func, nd) => nd.LastName = func("lastName")
    );
}

或者，您可以使用 XML 库并简单地定义如何通过属性和映射来填充字段。

Answer 3

您可以创建一个属性来确定应该使用哪个 XPath 表达式。示例：

[XPathSelector("document/employee/projects/project")]
internal class Projects
{
    public int Id { get; set; }
    public string Product { get; set; }
    public string Price { get; set; }
}

然后您可以通过反射使用它（代码未经测试，此处没有可用的 c# 编译器）：

private static T GetNode<T>(XNode content)
    : where T : new()
{
    var selector = typeof(T).GetCustomProperty<XPathSelector>();
    var element = content.XPathSelectElement(selector.XPathSelector);

    var ret = new T();

    foreach (var child in element.Elements) {
        var property = typeof(T).GetProperties().Single(p => p.Name.ToLower() == child.Name.ToLower());

        property.SetValue(ret, child.GetElementAsString(child.Name));
    }   

    return ret;
}