我试图创建一个通用扩展，使用'TryParse'来检查字符串是否为给定类型:
public static bool Is<T>(this string input)
{
T notUsed;
return T.TryParse(input, out notUsed);
}
这将无法编译，因为它无法解析符号TryParse
据我所知，“TryParse”不是任何接口的一部分。
这有可能吗?
更新:
使用以下我想出的答案:
public static bool Is<T>(this string input)
{
try
{
TypeDescriptor.GetConverter(typeof(T)).ConvertFromString(input);
}
catch
{
return false;
}
return true;
}
它工作得很好，但我认为以这种方式使用异常对我来说不合适。
更新2:
修改为传递类型而不是使用泛型:
public static bool Is(this string input, Type targetType)
{
try
{
TypeDescriptor.GetConverter(targetType).ConvertFromString(input);
return true;
}
catch
{
return false;
}
}
这是另一个选择。
我编写了一个类，可以轻松注册任意数量的TryParse处理程序。它让我这样做:
var tp = new TryParser();
tp.Register<int>(int.TryParse);
tp.Register<decimal>(decimal.TryParse);
tp.Register<double>(double.TryParse);
int x;
if (tp.TryParse("42", out x))
{
Console.WriteLine(x);
};
我将42打印到控制台。
这个类是:
public class TryParser
{
public delegate bool TryParseDelegate<T>(string s, out T result);
private Dictionary<Type, Delegate> _tryParsers = new Dictionary<Type, Delegate>();
public void Register<T>(TryParseDelegate<T> d)
{
_tryParsers[typeof(T)] = d;
}
public bool Deregister<T>()
{
return _tryParsers.Remove(typeof(T));
}
public bool TryParse<T>(string s, out T result)
{
if (!_tryParsers.ContainsKey(typeof(T)))
{
throw new ArgumentException("Does not contain parser for " + typeof(T).FullName + ".");
}
var d = (TryParseDelegate<T>)_tryParsers[typeof(T)];
return d(s, out result);
}
}
借用自http://blogs.msdn.com/b/davidebb/archive/2009/10/23/using-c-dynamic-to-call-static-members.aspx
当遵循这个参考:如何调用静态方法在c# 4.0与动态类型?
using System;
using System.Collections.Generic;
using System.Dynamic;
using System.Linq;
using System.Reflection;
namespace Utils
{
public class StaticMembersDynamicWrapper : DynamicObject
{
private Type _type;
public StaticMembersDynamicWrapper(Type type) { _type = type; }
// Handle static methods
public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result)
{
var methods = _type
.GetMethods(BindingFlags.FlattenHierarchy | BindingFlags.Static | BindingFlags.Public)
.Where(methodInfo => methodInfo.Name == binder.Name);
var method = methods.FirstOrDefault();
if (method != null)
{
result = method.Invoke(null, args);
return true;
}
result = null;
return false;
}
}
public static class StaticMembersDynamicWrapperExtensions
{
static Dictionary<Type, DynamicObject> cache =
new Dictionary<Type, DynamicObject>
{
{typeof(double), new StaticMembersDynamicWrapper(typeof(double))},
{typeof(float), new StaticMembersDynamicWrapper(typeof(float))},
{typeof(uint), new StaticMembersDynamicWrapper(typeof(uint))},
{typeof(int), new StaticMembersDynamicWrapper(typeof(int))},
{typeof(sbyte), new StaticMembersDynamicWrapper(typeof(sbyte))}
};
/// <summary>
/// Allows access to static fields, properties, and methods, resolved at run-time.
/// </summary>
public static dynamic StaticMembers(this Type type)
{
DynamicObject retVal;
if (!cache.TryGetValue(type, out retVal))
return new StaticMembersDynamicWrapper(type);
return retVal;
}
}
}
使用方法如下:
public static T? ParseNumeric<T>(this string str, bool throws = true)
where T : struct
{
var statics = typeof(T).StaticMembers();
if (throws) return statics.Parse(str);
T retval;
if (!statics.TryParse(str, out retval)) return null;
return retval;
}
我使用Charlie Brown的答案作为Json.NET的JObject扩展方法。
public static class JObjectExtension
{
public delegate bool TryParseHandler<T>(string value, out T result);
public static bool TryParsePropertyAs<T>(
this JObject jObject,
string propertyName,
TryParseHandler<T> parser,
out T value)
{
value = default;
if (!jObject.TryGetValue(propertyName, out var jToken)) return false;
if (!parser(jToken.Value<string>(), out T result)) return false;
value = result;
return true;
}
}
