在switch语句中使用NSString

switch语句的大小写需要整型常量,因此这里不能使用NSString,因此似乎必须使用if/else选项。

还有一点是,必须使用isEqualToString:或compare:方法比较nsstring,因此即使允许开关情况下使用指针值,也不能使用它们

我在应用程序中使用这些宏。

#define CASE(str)                       if ([__s__ isEqualToString:(str)]) 
#define SWITCH(s)                       for (NSString *__s__ = (s); ; )
#define DEFAULT   

SWITCH (string) {
    CASE (@"AAA") {
        break;
    }
    CASE (@"BBB") {
        break;
    }
    CASE (@"CCC") {
        break;
    }
    DEFAULT {
        break;
    }
 }

回应并支持@Cur的回答。。这是相同的东西,但是用Xcode 4.4+编写/ clang / 无论什么 “字面语法”,即 更接近 到一个简单的骨灰盒 if, else 比较(这就是重点,不是吗…)

NSDictionary *actionD = @{ @"A" : ^{ NSLog(@"BlockA!"); }, 
                           @"B" : ^{ NSLog(@"BlockB!"); }};

((void(^)()) actionD[@"A"])(); 

BlockA!

或者说,您希望根据按钮的标题执行选择器。。。

- (IBAction) multiButtonTarget:button { 

((void (^)())                           // cast
  @{ @"Click?" : ^{ self.click; }, 
     @"Quit!"  : ^{   exit(-1); }}      // define
        [((NSButton*)button).title])    // select
                                    (); // execute
}

别说了! ⟹ exit -1

简短,就像 w.string = kIvar == 0 ? @"StringA" : @"StringB"; ,而且更有用,因为你可以在那里推块,甚至不考虑一些可怕的(有限的,复杂的) @selector !

编辑:这更明显是这样构造的:

[@[ @"YES", @"NO", @"SIRPOOPSALOT"] do:^(id maybe) {
    [maybe isEqual:@"YES"] ? ^{ NSLog(@"You got it!"); }()
  : [maybe isEqual:@"NO" ] ? ^{ NSLog(@"You lose!!!"); }() 
  :                          ^{ NSLog(@"Not sure!"); [self tryAgain]; }();
}]; 

➜ *** You got it! *** ➜ *** You lose!!! *** ➜ *** Not sure! ***

我不得不承认,我 令人难堪 进入 这种句法上的愚蠢。 另一种选择是忘记字符串是什么。。执行它,哈哈。。。

[ @{ NSApplicationWillBecomeActiveNotification : @"slideIn",
     NSApplicationDidResignActiveNotification  : @"slideOut" } each:^( id key, id obj ) {
    [w observeObject:NSApp forName:obj calling: NSSelectorFromString ( obj ) ];       
}];

或者直接用用户界面的话来说。。

- (IBAction)setSomethingLiterallyWithSegmentedLabel:(id)sender {
   NSInteger selectedSegment = [sender selectedSegment];
   BOOL isSelected = [sender isSelectedForSegment:selectedSegment];
   BOOL *optionPtr = &isSelected;
   SEL fabricated = NSSelectorFromString
       ([NSString stringWithFormat:@"set%@:",[sender labelForSegment:selectedSegment]]);
   [self performSelector:fabricated withValue:optionPtr];
}

Switch语句不能用于NSString:它只能用于int。

If/Else语句是太多的代码,通常不是最佳的。

最佳解决方案是使用由NSString(或其他对象)可能性索引的NSDictionary。然后直接访问正确的值/函数。

示例1,当您要测试@“A”或@“B”并执行methodA或methodB时:

NSDictionary *action = @{@"A" : [NSValue valueWithPointer:@selector(methodA)],
                         @"B" : [NSValue valueWithPointer:@selector(methodB)],
                         };
[self performSelector:[action[stringToTest] pointerValue]];

示例2,当您要测试@“A”或@“B”并执行blockA或blockB时:

NSDictionary *action = @{@"A" : ^{ NSLog (@"Block A"); },
                         @"B" : ^{ NSLog (@"Block B"); },
                         };
((void (^)())action[stringToTest])();

受alex gray的启发,我创建了一个category方法,它将链式过滤器应用于其对象:

.h.小时

#import <Foundation/Foundation.h>
typedef id(^FilterBlock)(id element,NSUInteger idx, BOOL *stop);

@interface NSObject (Functional)
-(id)processByPerformingFilterBlocks:(NSArray *)filterBlocks;
@end

.m.公司

#import "NSObject+Functional.h"

@implementation NSObject (Functional)
-(id)processByPerformingFilterBlocks:(NSArray *)filterBlocks
{
    __block id blockSelf = self;
    [filterBlocks enumerateObjectsUsingBlock:^( id (^block)(id,NSUInteger idx, BOOL*) , NSUInteger idx, BOOL *stop) {
        blockSelf = block(blockSelf, idx, stop);
    }];

    return blockSelf;
}
@end

你可以把它当作

FilterBlock fb1 = ^id(id element, NSUInteger idx, BOOL *stop){ if ([element isEqualToString:@"YES"]) { NSLog(@"You did it");  *stop = YES;} return element;};
FilterBlock fb2 = ^id(id element, NSUInteger idx, BOOL *stop){ if ([element isEqualToString:@"NO"] ) { NSLog(@"Nope");        *stop = YES;} return element;};

NSArray *filter = @[ fb1, fb2 ];
NSArray *inputArray = @[@"NO",@"YES"];

[inputArray enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
    [obj processByPerformingFilterBlocks:filter];
}];

但你也可以做一些更复杂的事情,比如简单的交叉计算:

FilterBlock b1 = ^id(id element,NSUInteger idx, BOOL *stop) {return [NSNumber numberWithInteger:[(NSNumber *)element integerValue] *2 ];};
FilterBlock b2 = ^id(NSNumber* element,NSUInteger idx, BOOL *stop) {
    *stop = YES;
    return [NSNumber numberWithInteger:[element integerValue]*[element integerValue]];
};
FilterBlock b3 = ^id(NSNumber* element, NSUInteger idx,BOOL *stop) {return [NSNumber numberWithInteger:[element integerValue]*[element integerValue]];};

NSArray *filterBlocks = @[b1,b2, b3, b3, b3];
NSNumber *numberTwo = [NSNumber numberWithInteger:2];
NSNumber *numberTwoResult = [numberTwo processByPerformingFilterBlocks:filterBlocks];    
NSLog(@"%@ %@", numberTwo, numberTwoResult);

我知道我去派对有点晚了,但这是我提交的一份关于objective-c switch声明。这有点复杂,所以忍受难看的宏。

特征:

• 看 就像一个交换语句
• 内置线程原子性
• 适用于所有objective-c对象,而不仅仅是 NSString (使用 -isEqual: 选择器)
• 也可以扩展到使用C-types,除非 struct s(因为他们没有 == 操作员)
• 每个switch语句只能计算一个case标签( break 不需要)
• 如果没有选择任何情况,就没有无限循环的机会( 打破 不需要)
• 只保留一个变量名, ____dontuse_switch_var (所有其他的都在静态作用域中,可以在本地作用域中覆盖)
• 不会导致任何奇怪的保留问题(使用 __weak 参考文献)

缺点:

• 非常 难以理解的来源
• 所有case语句都是在选择一个之前评估的(因此将最频繁的语句放在顶部)
• 线程原子性是以性能为代价的—它不需要任何锁,但它确实使用 NSThread 相当广泛。
• 不使用括号 { 或 } ,Xcode不喜欢正确格式化语句(这是由于 goto 贴上标签。
• 不只是标题(需要一个 .m 工作文件,用于 NSValue 弱引用)

例子:

#include "OBJC_SWITCH.h"

int main()
{
    NSArray *items = @[ @"A", @"B", @"C", @"D", @"E", @"F" ];

    for (int i = 0; i < items.count; i++)
    {
        $switch(items[i]) {
            $case(@"A"):
            {
                NSLog(@"It was A!");
                break;
            }
            $case(@"B"): // no brackets, no break, still works
                NSLog(@"It was B!");

            $case(@"C"): // continue works as well, there's no difference
            {
                NSLog(@"It was C!");
                continue;
            }

            $default: // brackets, but no break.
            {
                NSLog(@"Neither A, B, or C.");
            } 
        }
    }
}

不用再麻烦了,下面是(丑陋的)代码:

OBJC_开关.h:

#import "NSValue+WeakRef.h"

// mapping of threads to the values being switched on
static NSMutableDictionary *____dontuse_switch_variable_dictionary;

// boolean flag to indicate whether or not to stop switching
static NSMutableDictionary *____dontuse_switch_bool_dictionary;

// simple function to return the current thread's switch value
static inline id current_thread_switch_value()
{
    // simple initializer block
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        if (!____dontuse_switch_variable_dictionary)
            ____dontuse_switch_variable_dictionary = [NSMutableDictionary dictionary];
    });

    return [[____dontuse_switch_variable_dictionary objectForKey:[NSValue valueWithWeakObject:[NSThread currentThread]]] weakObjectValue];
}

// simple function to set the current thread's switch value
static inline void set_current_thread_switch_value(id val)
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        if (!____dontuse_switch_variable_dictionary)
            ____dontuse_switch_variable_dictionary = [NSMutableDictionary dictionary];
    });

    [____dontuse_switch_variable_dictionary setObject:[NSValue valueWithWeakObject:val] forKey:[NSValue valueWithWeakObject:[NSThread currentThread]]];
}

// check if the current thread has switched yet
static inline BOOL current_thread_has_switched()
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        if (!____dontuse_switch_bool_dictionary)
            ____dontuse_switch_bool_dictionary = [NSMutableDictionary dictionary];
    });

    return [[____dontuse_switch_bool_dictionary objectForKey:[NSValue valueWithWeakObject:[NSThread currentThread]]] boolValue];
}

// set the current thread's switch state
static inline void set_current_thread_has_switched(BOOL b)
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        if (!____dontuse_switch_bool_dictionary)
            ____dontuse_switch_bool_dictionary = [NSMutableDictionary dictionary];
    });

    [____dontuse_switch_bool_dictionary setObject:[NSNumber numberWithBool:b] forKey:[NSValue valueWithWeakObject:[NSThread currentThread]]];
}

// concatenate two tokens
#define $_concat(A, B) A ## B
#define $concat(A, B) $_concat(A, B)

/* start of switch statement */
#define $switch(value) { \
/* set this thread's switch value */ \
set_current_thread_switch_value(value); \
/* make sure we reset the switched value for the thread */ \
set_current_thread_has_switched(0); \
/* if statement to ensure that there is a scope after the `switch` */ \
} if (1)

/* a case 'label' */
#define $case(value) \
/* make sure we haven't switched yet */ \
if(!current_thread_has_switched() && \
/* check to see if the values are equal */ \
[current_thread_switch_value() isEqual:value]) \
/* basically, we are creating a 'for' loop that only iterates once, so that we support the 'break' statement, without any harm */ \
/* this also sets the 'switched' value for this thread */ \
for (int ____dontuse_switch_var = 0; set_current_thread_has_switched(1), ____dontuse_switch_var != 1; ____dontuse_switch_var++) \
/* this creates the case label (which does nothing) so that it 'looks' like a switch statement. */ \
/* technically, you could to a goto with this, but I don't think anyone would purposely do that */ \
$concat(__objc_switch_label, __COUNTER__)

/* the default 'label' */
#define $default \
/* this only evaluates if we haven't switched yet (obviously) */ \
if (!current_thread_has_switched()) \
/* exact same loop as for the 'case' statement, which sets that we have switched, and only executes once. */ \
for (int ____dontuse_switch_var = 0; set_current_thread_has_switched(1), ____dontuse_switch_var != 1; ____dontuse_switch_var++) \
/* once again, create a case label to make it look like a switch statement */ \
$concat(__objc_switch_label, __COUNTER__)

我不打算为此提供文档,因为这是非常不言而喻的。如果真的很难理解,请留下注释,我将记录代码。

NSValue+WeakRef.h码:

#import <Foundation/Foundation.h>

@interface NSValue(WeakRef)

+(id) valueWithWeakObject:(__weak id) val;
-(id) initWithWeakObject:(__weak id) val;

-(__weak id) weakObjectValue;

@end

NSValue+WeakRef.m公司:

#import "NSValue+WeakRef.h"

@interface ConcreteWeakValue : NSValue
{
    __weak id _weakValue;
}

@end

@implementation NSValue(WeakRef)

+(id) valueWithWeakObject:(id) val
{
    return [ConcreteWeakValue valueWithWeakObject:val];
}

-(id) initWithWeakObject:(id)val
{
    return [NSValue valueWithWeakObject:val];
}

-(id) weakObjectValue
{
    [self doesNotRecognizeSelector:_cmd];

    return nil;
}

@end

@implementation ConcreteWeakValue

+(id) valueWithWeakObject:(__weak id)val
{
    return [[self alloc] initWithWeakObject:val];
}

-(id) initWithWeakObject:(__weak id)val
{
    if ((self = [super init]))
    {
        _weakValue = val;
    }

    return self;
}

-(const char *) objCType
{
    return @encode(__weak id);
}

-(__weak id) weakObjectValue
{
    return _weakValue;
}

-(void) getValue:(void *)value
{
    * ((__weak id *) value) = _weakValue;
}

-(BOOL) isEqual:(id)object
{
    if (![object isKindOfClass:[self class]])
        return NO;

    return [object weakObjectValue] == [self weakObjectValue];
}

@end

正如其他人所指出的,使用if/else可能是最简单的,但是 可以 创建类似switch语句的语句。我在GitHub上创建了一个项目,它正是这样做的: WSLObjectSwitch . 这是一个相当幼稚的实现,它没有优化使用散列等,但它确实有效。

这通常是我使用枚举之类的东西的地方。如果必须管理这么多值,我只需创建一个枚举,该枚举的名称与否则传递给它的字符串的名称相同,然后在其中传递它,例如:

enum {
    EGLFieldSelectionToolbarItem = 0,
    EGLTextSelectionToolbarItem,
};
+(NSImage *)iconForIdentifier:(int)alias WithSize:(NSSize)size; //Alias should be an enum value with the same name
NSImage *icon = [[NSImage alloc]initWithSize:size];
  NSBezierPath *bezierPath = [NSBezierPath bezierPath];
[icon lockFocus];
switch (alias) {
    case EGLFieldSelectionToolbarItem:
        …//Drawing code
        break;
    case EGLTextSelectionToolbarItem:
        …//More drawing code
    default:
        break;
}
[bezierPath stroke];
[icon unlockFocus];
return icon;
}

您可以使用按钮的标记在不同操作的按钮之间轻松切换。

例子:

- (IBAction)addPost:(id)sender {
switch ([sender tag]) {
    case 1:
        break;
    case 2:
        break;
    case 3:
        break;
    case 4:
        break;
    case 5:
        break;
    default:
        break;
}

}