0

我有一些工厂代码根据代表枚举的类成员的值创建对象：

public enum BeltPrinterType
{
    None,
    ZebraQL220,
    ONiel
    // add more as needed
}

public static BeltPrinterType printerChoice = BeltPrinterType.None;

public class BeltPrinterFactory : IBeltPrinterFactory
{
    // http://stackoverflow.com/questions/17955040/how-can-i-return-none-as-a-default-case-from-a-factory?noredirect=1#comment26241733_17955040
    public IBeltPrinter NewBeltPrinter()
    {
        switch (printerChoice)
        {
            case BeltPrinterType.ZebraQL220: 
                return new ZebraQL220Printer();
            case BeltPrinterType.ONiel: 
                return new ONielPrinter();
            default: 
                return new None();
        }
    }
}

我需要在调用 NewBeltPrinter() 之前设置 printerChoice 的值 - 也就是说，如果它已从其默认的“None”值更改。所以我试图根据字符串表示来分配该值，但已经达到了这种尝试没有继续的众所周知的点：

string currentPrinter = AppSettings.ReadSettingsVal("beltprinter");
Type type = typeof(PrintUtils.BeltPrinterType);
foreach (FieldInfo field in type.GetFields(BindingFlags.Static | BindingFlags.Public))
{
    string display = field.GetValue(null).ToString();
    if (currentPrinter == display)
    {
        //PrintUtils.printerChoice = (type)field.GetValue(null);
        PrintUtils.printerChoice = ??? what now ???
        break;
    }
}

我已经尝试了我能想到的一切，但得到的回报只是编译器不断的谴责，这几乎是把我当作一个无赖和一个可悲的流氓。

有人知道我应该用什么代替问号吗？

4

4 回答 4

2

就这个而不是你的第二个代码块怎么样：

PrintUtils.printerChoice = (PrintUtils.BeltPrinterType)
    Enum.Parse(typeof(PrintUtils.BeltPrinterType),
               AppSettings.ReadSettingsVal("beltprinter"));
于 2013-08-02T22:17:27.110 回答
1

使用Enum.Parse将字符串转换为枚举值。（或Enum.TryParse尝试在未解析时不引发异常的情况下执行此操作）

编辑

如果您没有可用的 Enum.Parse，那么您必须自己进行转换：

switch (stringValue)
{
    case "BeltPrinterType.ONiel": enumValue = BeltPrinterType.ONiel; break;
    ...etc...
}
于 2013-08-02T22:17:46.913 回答
1

我无法编译为 .NET 1.1，但这似乎适用于 2.0

PrintUtils.printerChoice = (BeltPrinterType)field.GetValue(null);

编辑：我刚刚意识到这基本上是您代码中的注释...但是是的，我真的不明白为什么即使在 1.1 中这也行不通

于 2013-08-03T00:23:26.140 回答
1

来自智能设备框架 1.x 代码库：

    public static object Parse(System.Type enumType, string value, bool ignoreCase)
    {
        //throw an exception on null value
        if(value.TrimEnd(' ')=="")
        {
            throw new ArgumentException("value is either an empty string (\"\") or only contains white space.");
        }
        else
        {
            //type must be a derivative of enum
            if(enumType.BaseType==Type.GetType("System.Enum"))
            {
                //remove all spaces
                string[] memberNames = value.Replace(" ","").Split(',');

                //collect the results
                //we are cheating and using a long regardless of the underlying type of the enum
                //this is so we can use ordinary operators to add up each value
                //I suspect there is a more efficient way of doing this - I will update the code if there is
                long returnVal = 0;

                //for each of the members, add numerical value to returnVal
                foreach(string thisMember in memberNames)
                {
                    //skip this string segment if blank
                    if(thisMember!="")
                    {
                        try
                        {
                            if(ignoreCase)
                            {
                                returnVal += (long)Convert.ChangeType(enumType.GetField(thisMember, BindingFlags.Public | BindingFlags.Static | BindingFlags.IgnoreCase).GetValue(null),returnVal.GetType(), null);
                            }
                            else
                            {
                                returnVal += (long)Convert.ChangeType(enumType.GetField(thisMember, BindingFlags.Public | BindingFlags.Static).GetValue(null),returnVal.GetType(), null);
                            }
                        }
                        catch
                        {
                            try
                            {
                                //try getting the numeric value supplied and converting it
                                returnVal += (long)Convert.ChangeType(System.Enum.ToObject(enumType, Convert.ChangeType(thisMember, System.Enum.GetUnderlyingType(enumType), null)),typeof(long),null);
                            }
                            catch
                            {
                                throw new ArgumentException("value is a name, but not one of the named constants defined for the enumeration.");
                            }
                            //
                        }
                    }
                }


                //return the total converted back to the correct enum type
                return System.Enum.ToObject(enumType, returnVal);
            }
            else
            {
                //the type supplied does not derive from enum
                throw new ArgumentException("enumType parameter is not an System.Enum");
            }
        }
    }
于 2013-08-03T16:45:52.393 回答