使用string.Contains()和switch()

Question

我正在使用C#应用程序

if ((message.Contains("test")))
{
   Console.WriteLine("yes");
} else if ((message.Contains("test2"))) {
   Console.WriteLine("yes for test2");
}

有什么办法可以改变switch()这些if()陈述吗？

Answer 1

不,switch语句需要编译时常量.该语句message.Contains("test")可以根据消息评估true或false,因此它不是常量,因此不能用作switch语句的"case".

Answer 2

纠正[先生]的最终语法 C]的答案.

随着VS2017RC及其C#7支持的发布,它以这种方式工作:

switch(message)
{
    case string a when a.Contains("test2"): return "no";
    case string b when b.Contains("test"): return "yes";
}

您应该选择案例订购,因为第一场比赛将被选中.这就是为什么在测试之前放置"test2"的原因.

Answer 3

如果你只是想使用switch/case,你可以做这样的事情,伪代码:

    string message = "test of mine";
    string[] keys = new string[] {"test2",  "test"  };

    string sKeyResult = keys.FirstOrDefault<string>(s=>message.Contains(s));

    switch (sKeyResult)
    {
        case "test":
            Console.WriteLine("yes for test");
            break;
        case "test2":
            Console.WriteLine("yes for test2");
            break;
    }

但是如果键的数量很大,你可以用字典替换它,如下所示:

static Dictionary<string, string> dict = new Dictionary<string, string>();
static void Main(string[] args)
{
    string message = "test of mine";      

    // this happens only once, during initialization, this is just sample code
    dict.Add("test", "yes");
    dict.Add("test2", "yes2"); 


    string sKeyResult = dict.Keys.FirstOrDefault<string>(s=>message.Contains(s));

    Console.WriteLine(dict[sKeyResult]); //or `TryGetValue`... 
 }

Answer 4

您可以先进行检查,然后根据需要使用开关.

例如:

string str = "parameter"; // test1..test2..test3....

if (!message.Contains(str)) return ;

然后

switch(str)
{
  case "test1" : {} break;
  case "test2" : {} break;
  default : {} break;
}

Answer 5

这将使用开关表达式在 C# 8 中工作

var message = "Some test message";

message = message switch
{
    string a when a.Contains("test") => "yes",
    string b when b.Contains("test2") => "yes for test2",
    _ => "nothing to say"
};

如需进一步参考 https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/switch-expression

Answer 6

使用 C# 简单而高效

 string sri = "Naveen";
    switch (sri)
    {
        case var s when sri.Contains("ee"):
           Console.WriteLine("oops! worked...");
        break;
        case var s when sri.Contains("same"):
           Console.WriteLine("oops! Not found...");
        break;
    }

Answer 7

string message = "This is test1";
string[] switchStrings = { "TEST1", "TEST2" };
switch (switchStrings.FirstOrDefault<string>(s => message.ToUpper().Contains(s)))
{
    case "TEST1":
        //Do work
        break;
    case "TEST2":
        //Do work
        break;
    default:
        //Do work
        break; 
}