如何使用反射从字符串转换为 Nullable?
我有以下代码可以在给定几乎任何值的情况下转换为几乎任何值类型。上面有相当多的代码来使用 IsAssignableFrom 等,所以这是最后的手段。
MethodInfo parse = t.GetMethod("Parse", new Type[] { typeof(string) });
if (parse != null)
{
object parsed = parse.Invoke(null, new object[] { value.ToString() });
return (T)parsed;
}
else
{
throw new InvalidOperationException("The value you specified is not a valid " + typeof(T).ToString());
}
当我想转换为像 long? 这样的可空类型时,问题就来了。
显然,长? 类没有解析方法。
如何从 nullable 的模板类型中提取解析方法?
编辑:
这是我试图通过的一小段测试:
[Test]
public void ConverterTNullable()
{
Assert.That((int?)1, Is.EqualTo(Converter<int?>.Convert(1)));
Assert.That((int?)2, Is.EqualTo(Converter<int?>.Convert(2.0d)));
Assert.That(3, Is.EqualTo(Converter<long>.Convert(3)));
Assert.That((object)null, Is.EqualTo(Converter<long?>.Convert("")));
Assert.That((object)null, Is.EqualTo(Converter<long?>.Convert(null)));
Assert.That((object)null, Is.EqualTo(Converter<long?>.Convert(DBNull.Value)));
Assert.That((long)1, Is.EqualTo(Converter<long?>.Convert("1")));
Assert.That((long)2, Is.EqualTo(Converter<long?>.Convert(2.0)));
Assert.That((long?)3, Is.EqualTo(Converter<long>.Convert(3)));
}
以及整个功能:
/// <summary>
/// Converts any compatible object to an instance of T.
/// </summary>
/// <param name="value">The value to convert.</param>
/// <returns>The converted value.</returns>
public static T Convert(object value)
{
if (value is T)
{
return (T)value;
}
Type t = typeof(T);
if (t == typeof(string))
{
if (value is DBNull || value == null)
{
return (T)(object)null;
}
else
{
return (T)(object)(value.ToString());
}
}
else
{
if (value is DBNull || value == null)
{
return default(T);
}
if (value is string && string.IsNullOrEmpty((string)value))
{
return default(T);
}
try
{
return (T)value;
}
catch (InvalidCastException)
{
}
if (Nullable.GetUnderlyingType(t) != null)
{
t = Nullable.GetUnderlyingType(t);
}
MethodInfo parse = t.GetMethod("Parse", new Type[] { typeof(string) });
if (parse != null)
{
object parsed = parse.Invoke(null, new object[] { value.ToString() });
return (T)parsed;
}
else
{
throw new InvalidOperationException("The value you specified is not a valid " + typeof(T).ToString());
}
}
}