获得NS_ENUM项目数量的优雅方式 [英] Elegant way of getting number of items for NS_ENUM

问题描述

有没有一种优雅的方法来获取NS_ENUM中的项目总数？最大值？

Is there an elegant way of getting the total number of items in a NS_ENUM? And the maximum value?

一些例子：

typedef NS_ENUM(NSInteger, MyEnum)
{
    MyEnumA = 0,
    MyEnumB = 1,
    MyEnumC = 2
};
// NumberOfItems(MyEnum) -> 3, MaximumValue(MyEnum) -> 2.


typedef NS_ENUM(NSInteger, MyEnum)
{
    MyEnumA,
    MyEnumB,
    MyEnumC
};
// NumberOfItems(MyEnum) -> 3, MaximumValue(MyEnum) -> 2.


typedef NS_ENUM(NSInteger, MyEnum)
{
    MyEnumA = 4,
    MyEnumB,
    MyEnumC
};
// NumberOfItems(MyEnum) -> 3, MaximumValue(MyEnum) -> 6.


typedef NS_ENUM(NSInteger, MyEnum)
{
    MyEnumA = 0,
    MyEnumB = 2,
    MyEnumC = 4
};
// NumberOfItems(MyEnum) -> 3, MaximumValue(MyEnum) -> 4.

推荐答案

不幸的是，C枚举（其中 NS_ENUM 宏是一个生成器）相当简单，没有反射。

Unfortunately, C enums (which NS_ENUM macro is a generator for) are rather simple, with no reflection.

如果你的枚举值是连续的，那么很简单获取使用限制值的项目数量：

If your enum values are consecutive, it's simple to get the number of items using limit values:

typedef NS_ENUM(NSInteger, MyEnum) {
    MyEnumA = 0,
    MyEnumB,
    MyEnumC,
    MyEnumMax 
};

NSUInteger numItems = MyNumMax;

但是，这不是一个理想的解决方案，因为当你写一个 / code>，如果您不添加案例MyEnumMax：（或 default：）。

However, this is not an ideal solution because when you write a switch, you will get a warning if you don't add a case MyEnumMax: (or default:).

最好的选择是为每个枚举创建信息函数：

Your best option then is to create info functions for every enum:

typedef NS_ENUM(NSInteger, MyEnum) {
    MyEnumA = 0,
    MyEnumB = 2,
    MyEnumC = 4,
};

NSUInteger MyEnumSize() {
   return 3;
}

您还可以使用一些高级宏技术，如 X-macros 以动态生成此功能。

You could also use some advanced macro techniques like X-macros to generate this function dynamically.

大警告：X-macros不简单，不易阅读，但功能强大。示例如下：

Big warning: X-macros are not simple, not easily readable but they are powerful. Example follows:

MyEnum.h

#define MY_ENUM_DEFINITIONS \
    NS_ENUM_X_VALUE(MyEnumA, = 0) \
    NS_ENUM_X_VALUE(MyEnumB,) \
    NS_ENUM_X_VALUE(MyEnumC, = 4)

#define NS_ENUM_X_VALUE(__NAME__, __INT_VALUE__) __NAME__ __INT_VALUE__,

typedef NS_ENUM(NSInteger, MyEnum) {
    MY_ENUM_DEFINITIONS
};

#undef NS_ENUM_X_VALUE

NSString * NSStringFromMyEnum(MyEnum value);
NSArray * MyEnumValues();
NSUInteger MyEnumSize();
NSUInteger MyEnumMin();
NSUInteger MyEnumMax();

MyEnum.m

#define NS_ENUM_X_VALUE(__NAME__, __INT_VALUE__) [__NAME__] = @#__NAME__,

static NSString* MyEnumStringTable[] = {
    MY_ENUM_DEFINITIONS
};

#undef NS_ENUM_X_VALUE

NSString * NSStringFromMyEnum(MyEnum value) {
    return MyEnumStringTable[value];
}

#define NS_ENUM_X_VALUE(__NAME__, __INT_VALUE__) @(__NAME__),

static NSOrderedSet * MyEnumValueSet() {
    static NSOrderedSet *valueSet = nil;
    static dispatch_once_t onceToken;

    dispatch_once(&onceToken, ^{
        valueSet = [[NSOrderedSet alloc] initWithObjects:
        MY_ENUM_DEFINITIONS
        nil];
    });

    return valueSet;
}

#undef NS_ENUM_X_VALUE


NSArray *MyEnumValues() {
    return [MyEnumValueSet() array];
}

NSUInteger MyEnumSize() {
    return MyEnumValueSet().count;
}

NSUInteger MyEnumMin() {
    return [MyEnumValueSet().firstObject unsignedIntegerValue];
}

NSUInteger MyEnumMax() {
    return [MyEnumValueSet().lastObject unsignedIntegerValue];
}

使用

NSLog(@"MyEnum size: %@", @(MyEnumSize()));
NSLog(@"MyEnum min: %@", @(MyEnumMin()));
NSLog(@"MyEnum max: %@", @(MyEnumMax()));

NSLog(@"MyEnumC value to string: %@", NSStringFromMyEnum(MyEnumC));

for (NSNumber *value in MyEnumValues()) {
    NSLog(@"Value listing: %@ => %@", NSStringFromMyEnum([value unsignedIntegerValue]), value);
}

现在您可以修改/添加/删除标题和所有功能中的值将自动更新。

Now you can modify/add/remove values in the header and all your functions will be updated automatically.

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