如何在C#中转换为通用参数？

Question

我正在尝试编写一种XElement以强类型方式获取值的泛型方法.这就是我所拥有的:

public static class XElementExtensions
{
    public static XElement GetElement(this XElement xElement, string elementName)
    {
        // Calls xElement.Element(elementName) and returns that xElement (with some validation).
    }

    public static TElementType GetElementValue<TElementType>(this XElement xElement, string elementName)
    {
        XElement element = GetElement(xElement, elementName);
        try
        {
            return (TElementType)((object) element.Value); // First attempt.
        }
        catch (InvalidCastException originalException)
        {
            string exceptionMessage = string.Format("Cannot cast element value '{0}' to type '{1}'.", element.Value,
                typeof(TElementType).Name);
            throw new InvalidCastException(exceptionMessage, originalException);
        }
    }
}

正如你所看到First attempt的那样GetElementValue,我试图从字符串 - >对象 - > TElementType.不幸的是,这不适用于整数测试用例.运行以下测试时:

[Test]
public void GetElementValueShouldReturnValueOfIntegerElementAsInteger()
{
    const int expectedValue = 5;
    const string elementName = "intProp";
    var xElement = new XElement("name");
    var integerElement = new XElement(elementName) { Value = expectedValue.ToString() };
    xElement.Add(integerElement);

    int value = XElementExtensions.GetElementValue<int>(xElement, elementName);

    Assert.AreEqual(expectedValue, value, "Expected integer value was not returned from element.");
}

GetElementValue<int>调用时我得到以下异常:

System.InvalidCastException:无法将元素值'5'强制转换为'Int32'.

我是否必须分别处理每个铸造案例(或至少是数字案例)？

Answer 1

您也可以尝试Convert.ChangeType

Convert.ChangeType(element.Value, typeof(TElementType))