Bitwise flags and Switch statement?

问题

I have the following code (example), and I'm really not comfortable with so many 'if' checks:

public enum Flags 
{
    p1 = 0x01,  // 0001
    p2 = 0x02,  // 0010  
    p3 = 0x04,  // 0100
    p4 = 0x08   // 1000
};      

public static void MyMethod (Flags flag)
{
    if ((flag & Flags.p1) == Flags.p1)
        DoSomething();

    if ((flag & Flags.p2) == Flags.p2)
        DosomethingElse();

    if ((flag & Flags.p3) == Flags.p3)
        DosomethingElseAgain();

    if ((flag & Flags.p4) == Flags.p4)
        DosomethingElseAgainAndAgain();
}

MyMethod(Flags.p1 | Flags.p3);

Is there some way, that i could use an 'switch' statement. Maybe if I convert them to strings, or use arrays?

回答1:

Something like this?

public static void MyMethod(Flags flag)
{
    // Define action-lookup
    var actionsByFlag = new Dictionary<Flags, Action>
    {
        { Flags.p1, DoSomething},
        { Flags.p2, DosomethingElse},
        { Flags.p3, DosomethingElseAgain},
        { Flags.p4, DosomethingElseAgainAndAgain},
    };

    // Find applicable actions
    var actions = actionsByFlag.Where(kvp => (flag & kvp.Key) == kvp.Key)
                               .Select(kvp => kvp.Value);

    //Execute applicable actions
    foreach (var action in actions)
       action();
}

EDIT: If the order of actions are important, an OrderBy clause may be required.

回答2:

Here's a variation on Ani's answer:

public static void MyMethod(Flags flag) 
{ 
    // Define action-lookup 
    var dict = new Dictionary<Flags, Action> 
    { 
        { Flags.p1, DoSomething}, 
        { Flags.p2, DosomethingElse}, 
        { Flags.p3, DosomethingElseAgain}, 
        { Flags.p4, DosomethingElseAgainAndAgain}, 
    }; 

    // Find applicable actions 
    var actions = from value in Enum.GetValues(typeof(Flags))
                  where flag.HasFlag(value)
                  select dict[value];

    //Execute applicable actions 
    foreach (var action in actions)
       action(); 
}

The important difference here is that it iterates over the defined values in the enumeration rather than the entries in the dictionary. That way if you add a new flag to the enum without adding it to the dictionary, you will get an exception when you try to use the new flag. And it always iterates in order of the flags.

来源：https://stackoverflow.com/questions/3846979/bitwise-flags-and-switch-statement

标签

enums

switch-statement

bit-manipulation