如何简化对字符串的测试条件：如果输入了一个，那么另一个也必须输入？

Question

我写了以下条件表达式。 它工作得很好......我正在尝试找出/学习一种减少代码量的聪明方法。 也许以高级方式使用一些 c# Boolean 逻辑运算符。

if ((!String.IsNullOrWhiteSpace(ProxyServer.ParameterValue) &&
     String.IsNullOrWhiteSpace(ProxyPort.ParameterValue))
    || (!String.IsNullOrWhiteSpace(ProxyPort.ParameterValue) &&
        String.IsNullOrWhiteSpace(ProxyServer.ParameterValue)))
{
    result = "If one is present, both must be entered for Proxy Server, Proxy Port.";
}

Answer 1

评估是否满足两个条件之一，但不是两者相等

( !a && b ) || ( a && !b )

您可以使用^ aka XOR ：一个或另一个，但不能同时使用。

  if ( string.IsNullOrWhiteSpace(ProxyServer.ParameterValue) ^ string.IsNullOrWhiteSpace(ProxyPort.ParameterValue) )
  {
    ...
  }

结果如下：

ProxyServer    ProxyPort    IsNotProvided(ProxyServer) ^ IsNotProvided(ProxyPort)

empty          empty        false
provided       empty        true
empty          provided     true
provided       provided     false

逻辑异或运算符（C# 语言参考）

德摩根定律

评估是否满足多个条件之一但并非所有条件都相等

要检查两个以上的值，您也许可以使用@itsme86 建议的 LINQ，否则此方法可以提高速度和 memory 性能：

static bool CheckIfOneIsProvidedAndSomeOthersNot(params string[] values)
{
  if ( values.Length < 2 ) return false; // or throw new Exception();
  bool firstIsNullOrWhiteSpace = string.IsNullOrWhiteSpace(values[0]);
  bool result = firstIsNullOrWhiteSpace ^ string.IsNullOrWhiteSpace(values[1]);
  if ( values.Length > 2 )
    for ( int index = 2; index < values.Length; index++ )
      result = result || ( firstIsNullOrWhiteSpace ^ string.IsNullOrWhiteSpace(values[index]) );
  return result;
}

测试

  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("", ""));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("a", ""));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("", "a"));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("a", "a"));
  Console.WriteLine();
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("", "", ""));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("a", "", ""));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("", "a", ""));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("", "", "a"));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("a", "a", ""));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("", "a", "a"));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("a", "", "a"));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("a", "a", "a"));
  Console.WriteLine();
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("", "", "", ""));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("a", "", "", ""));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("", "a", "", ""));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("", "", "a", ""));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("", "", "", "a"));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("a", "a", "", ""));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("", "a", "a", ""));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("", "", "a", "a"));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("a", "", "a", ""));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("", "a", "", "a"));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("", "a", "a", ""));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("a", "a", "a", ""));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("", "a", "a", "a"));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("a", "", "a", "a"));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("a", "a", "", "a"));
  Console.WriteLine(CheckIfOneIsProvidedAndSomeOthersNot("a", "a", "a", "a"));

（希望我不要忘记组合......）

Output

False
True
True
False

False
True
True
True
True
True
True
False

False
True
True
True
True
True
True
True
True
True
True
True
True
True
True
False

具有泛型和委托的版本

static bool CheckIfOneIsTrueButNotAllAreEqual<T>(Func<T, bool> check, params T[] values)
{
  if ( values.Length < 2 ) return false; // or throw new Exception();
  bool resultFirst = check(values[0]);
  bool result = resultFirst ^ check(values[1]);
  if ( values.Length > 2 )
    for ( int index = 2; index < values.Length; index++ )
      result = result || ( resultFirst ^ check(values[index]) );
  return result;
}

用法

Console.WriteLine(CheckIfOneIsTrueButNotAllAreEqual(string.IsNullOrWhiteSpace, "", ""));
Console.WriteLine(CheckIfOneIsTrueButNotAllAreEqual(string.IsNullOrWhiteSpace, "a", ""));
Console.WriteLine(CheckIfOneIsTrueButNotAllAreEqual(string.IsNullOrWhiteSpace, "", "a"));
Console.WriteLine(CheckIfOneIsTrueButNotAllAreEqual(string.IsNullOrWhiteSpace, "a", "a"));