c# - 从字符串返回多种类型之一

Question

我有一个通用的方法。

private T Blah<T>()

在这种方法中，我有一个要返回的字符串，但问题是它T可能不是字符串。值T可以是string、int、DateTime和DateTime?。decimal?

我该如何处理这个字符串，以便我可以返回它并支持所有这些类型？

Answer 1

  private T Blah<T> () where T : IConvertible
  {            
     if (!String.IsNullOrEmpty(source))
          return (T)Convert.ChangeType(source, typeof(T));
     return default(T);
  }

应该适用于所有这些类型。

Answer 2

这可能会有所帮助：

private T Blah<T>(Func<string, T> map)
{   
    //Your codes here

    return map(yourString); //yourString: the string which you are going to convert
}

在这里你称之为：

//For int
Blah(input => int.Parse(input));

//For DateTime
Blah(input => DateTime.Parse(input));

Answer 3

我Blah<T> 公开测试，根据您的要求进行修改。

• 代码

  partial class SomeClass {
      public T Blah<T>() {
          var t="2013 03 30";
  
          return (T)(typeof(String).Equals(typeof(T))?t as object:(
              from args in new[] { new object[] { t, default(T) } }
              let type=Nullable.GetUnderlyingType(typeof(T))??typeof(T)
              let types=new[] { typeof(String), type.MakeByRefType() }
              let bindingAttr=BindingFlags.Public|BindingFlags.Static
              let tryParse=type.GetMethod("TryParse", bindingAttr, default(Binder), types, null)
              let b=typeof(DateTime)!=type
              let dummy=b?args[0]=((String)args[0]).Split('\x20').Aggregate(String.Concat):""
              let success=null!=tryParse?tryParse.Invoke(typeof(T), args):false
              select args.Last()).Last());
      }
  }
  

  partial class TestClass {
      public static void TestMethod() {
          var x=new SomeClass();
  
          Console.WriteLine("x.Blah<String>() = {0}", x.Blah<String>());
          Console.WriteLine("x.Blah<int>() = {0}", x.Blah<int>());
          Console.WriteLine("x.Blah<DateTime>() = {0}", x.Blah<DateTime>());
          Console.WriteLine("x.Blah<DateTime?>() = {0}", x.Blah<DateTime?>());
          Console.WriteLine("x.Blah<decimal?>() = {0}", x.Blah<decimal?>());
      }
  }
  

• 输出

  x.Blah<String>() = 2013 03 30
  x.Blah<int>() = 20130330
  x.Blah<日期时间>() = 2013/3/30 0:00:00
  x.Blah<DateTime?>() = 2013/3/30 0:00:00
  x.Blah<十进制？>() = 20130330
  

The special thing is that I removed the spaces if destination type is not DateTime or DateTime?.

You can even try with x.Blah<long>() which is not in your requirement, and any other types. Let me know if you found any type can cause an exception.