blocks|key|1086551|text|switch语句需要整数常量，所以这里不能使用NSString，所以看起来你必须使用if/else选项。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1086552|还有一点是，您必须使用isEqualToString:或NSStrings+:方法比较比较，因此即使允许在切换情况下使用指针值，您也不能使用它们|1086553|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

switch statement requires integer constants for it cases so NSString cannot be used here, so it seems you have to go for if/else option. 

One more point is you must compare NSStrings using isEqualToString: or compare: method, so even if pointer values have been allowed for switch cases you could not use them anyway

blocks|key|1086661|text|我在我的应用程序中使用这些宏。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1086662|#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;
++++}
+}|code-block|syntax|javascript|1086663|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I use these macros in my app.

<pre><code>#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;
 }
 }
</code></pre>

blocks|key|871857|text|Switch语句不适用于NSString:它只适用于int。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|871858|If/Else语句的代码太多，而且通常不是最优的。|871859|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。|871860|示例1，当您想测试@"A“或@"B”并执行methodA或methodB时：|871861|NSDictionary+*action+=+@{@"A"+:+[NSValue+valueWithPointer:@selector(methodA)],
+++++++++++++++++++++++++@"B"+:+[NSValue+valueWithPointer:@selector(methodB)],
+++++++++++++++++++++++++};
[self+performSelector:[action[stringToTest]+pointerValue]];|code-block|syntax|javascript|871862|示例2，当您想测试@"A“或@"B”并执行blockA或blockB时：|871863|NSDictionary+*action+=+@{@"A"+:+%5E{+NSLog+(@"Block+A");+},
+++++++++++++++++++++++++@"B"+:+%5E{+NSLog+(@"Block+B");+},
+++++++++++++++++++++++++};
((void+(%5E)())action[stringToTest])();|871864|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|U|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|V|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|W|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|J|7|Y|8|@]|9|@]|A|$K|L]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Switch statement wouldn't work with NSString: it works only with int.

If/Else statement is too much code and often not optimal.

Optimal solution is to use an NSDictionary indexed by the NSString (or other objects) possibilities. Then you directly access the right value/function.

Example 1, when you want to test for @"A" or @"B" and perform methodA or methodB:

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

Example 2, when you want to test for @"A" or @"B" and perform blockA or blockB:

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

blocks|key|1086706|text|受到alex+gray的启发，我创建了一个类别方法，将链接的滤镜应用于其对象：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1086707|.h|1086708|#import+<Foundation/Foundation.h>
typedef+id(%5EFilterBlock)(id+element,NSUInteger+idx,+BOOL+*stop);

@interface+NSObject+(Functional)
-(id)processByPerformingFilterBlocks:(NSArray+*)filterBlocks;
@end|code-block|syntax|javascript|1086709|.m|1086710|#import+"NSObject%2BFunctional.h"

@implementation+NSObject+(Functional)
-(id)processByPerformingFilterBlocks:(NSArray+*)filterBlocks
{
++++__block+id+blockSelf+=+self;
++++[filterBlocks+enumerateObjectsUsingBlock:%5E(+id+(%5Eblock)(id,NSUInteger+idx,+BOOL*)+,+NSUInteger+idx,+BOOL+*stop)+{
++++++++blockSelf+=+block(blockSelf,+idx,+stop);
++++}];

++++return+blockSelf;
}
@end|1086711|您可以将其用作|1086712|FilterBlock+fb1+=+%5Eid(id+element,+NSUInteger+idx,+BOOL+*stop){+if+([element+isEqualToString:@"YES"])+{+NSLog(@"You+did+it");++*stop+=+YES;}+return+element;};
FilterBlock+fb2+=+%5Eid(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:%5E(id+obj,+NSUInteger+idx,+BOOL+*stop)+{
++++[obj+processByPerformingFilterBlocks:filter];
}];|1086713|但是你也可以做更复杂的事情，比如复杂的计算：|1086714|FilterBlock+b1+=+%5Eid(id+element,NSUInteger+idx,+BOOL+*stop)+{return+[NSNumber+numberWithInteger:[(NSNumber+*)element+integerValue]+*2+];};
FilterBlock+b2+=+%5Eid(NSNumber*+element,NSUInteger+idx,+BOOL+*stop)+{
++++*stop+=+YES;
++++return+[NSNumber+numberWithInteger:[element+integerValue]*[element+integerValue]];
};
FilterBlock+b3+=+%5Eid(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(@"%25@+%25@",+numberTwo,+numberTwoResult);|1086715|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|11|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|13|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|14|8|@]|9|@]|A|$G|H]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

inspired by alex gray, I created a category method, that applies chained filters to its object:

.h

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

@interface NSObject (Functional)
-(id)processByPerformingFilterBlocks:(NSArray *)filterBlocks;
@end
</code></pre>

.m

<pre><code>#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
</code></pre>

You can use it as 

<pre><code>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];
}];
</code></pre>

but you can also do more complicated stuff, like aplied chianed calculations:

<pre><code>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);
</code></pre>

blocks|key|1086794|text|这通常是我使用枚举之类的东西的地方。如果我必须管理这么多的值，我只需创建一个枚举，它的名称与我原本要传递的字符串同名，并将其传递到其中，例如：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1086795|enum+{
++++EGLFieldSelectionToolbarItem+=+0,
++++EGLTextSelectionToolbarItem,
};
%2B(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;
}|code-block|syntax|javascript|1086796|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This is typically where I use something like an enum. If I have to manage that many values, I just create an enum with the same name as the string I would have passed otherwise and pass it in there, for example:

<pre><code>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;
}
</code></pre>

blocks|key|1086817|text|您可以使用按钮的标签轻松地在按钮之间切换以执行不同的操作。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1086818|示例：|1086819|-+(IBAction)addPost:(id)sender+{
switch+([sender+tag])+{
++++case+1:
++++++++break;
++++case+2:
++++++++break;
++++case+3:
++++++++break;
++++case+4:
++++++++break;
++++case+5:
++++++++break;
++++default:
++++++++break;
}|code-block|syntax|javascript|1086820|}|1086821|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

you can easily switch between buttons for different action using their tags. 

Example : 

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

}

Is it possible to use an <code>NSString</code> in a <code>switch</code> statement?

Or is it better to just use <code>if</code> / <code>else if</code>?

Using an NSString in a switch statement

是否可以在switch语句中使用NSString？还是只使用if / else if更好

问在switch语句中使用NSString
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回答 6

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问在switch语句中使用NSString
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