这次项目中遇到一个需求，将数字每隔3个用逗号隔开。因为如果数字太大确实看着有点眼花。
　　所以就想着写了一个NSString的category，用起来效果还不错，代码如下：

.h的声明

#import <Foundation/Foundation.h>

@interface NSString (NumberSplitWithComma)
/**
 *数字以逗号隔开 例：123，321.11
 */
- (NSString *)ld_numberSplitWithComma;
/**
 *@param puctutation 符合
 *数字以某个符合隔开 例：123，321.11
 */
- (NSString *)ld_numberSplitWithPunctutaion:(NSString *)puctutation;
@end

.m文件的实现

#import "NSString+NumberSplitWithComma.h"

@implementation NSString (NumberSplitWithComma)

- (NSString *)ld_numberSplitWithComma{
    if ([self private_isNumber]) {
        NSMutableString *muString = [NSMutableString tringWithString:self];
        return [self private_insert:muString withPunctuation:@","];
    }else{
        return self;
    }
}
- (NSString *)ld_numberSplitWithPunctutaion:(NSString *)puctutation{
    if ([self private_isNumber]) {
         NSMutableString *muString = [NSMutableString stringWithString:self];
         return [self private_insert:muString withPunctuation:puctutation];
     }else{
         return self;
     }
}
- (NSMutableString *)private_insert:(NSMutableString *)string withPunctuation:(NSString *)punctuation{
    NSUInteger maxLength = string.length;
    if ([string containsString:punctuation]) {
        maxLength = [string rangeOfString:punctuation].location;
    }else if ([string containsString:@"."]){
        maxLength = [string rangeOfString:@"."].location;
    }
    if (maxLength-([string containsString:@"-"]?1:0)>3) {
        [string insertString:punctuation atIndex:(maxLength-3)];
        [self private_insert:string withPunctuation:punctuation];
    }else{
        return string;
    }
    return string;
}
 - (Boolean)private_isNumber{
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF MATCHES %@",@"^[-0-9.]*$"];
    if ([predicate evaluateWithObject:self]) {
        return YES;
     }
    return NO;
 }

补充

有简友反应可以使用NSNumberFormatter，然后研究了一番，确实能够很方便的达到效果。
1、通过使用formatter style，苹果帮我们定义好的格式。

NSNumberFormatter *numberFormatter =   [[NSNumberFormatter alloc] init];
[numberFormatter setNumberStyle:NSNumberFormatterDecimalStyle];
NSString *formattedNumberString = [numberFormatter stringFromNumber:@122344.4563];
NSLog(@"formattedNumberString: %@", formattedNumberString);
// Output for locale en_US: "formattedNumberString: formattedNumberString: 122,344.453"

NSNumberFormatter 的numberStyle是一个枚举

     typedef NS_ENUM(NSUInteger, NSNumberFormatterStyle) {
 NSNumberFormatterNoStyle = kCFNumberFormatterNoStyle,四舍五入
 NSNumberFormatterDecimalStyle = kCFNumberFormatterDecimalStyle,金额 100,200,300.123
 NSNumberFormatterCurrencyStyle = kCFNumberFormatterCurrencyStyle,货币 $100,200,300.12
 NSNumberFormatterPercentStyle = kCFNumberFormatterPercentStyle,百分比 12%
 NSNumberFormatterScientificStyle = kCFNumberFormatterScientificStyle,科学计数法 1.234E8
 NSNumberFormatterSpellOutStyle = kCFNumberFormatterSpellOutStyle,口语 One...
 NSNumberFormatterOrdinalStyle NS_ENUM_AVAILABLE(10_11, 9_0) = kCFNumberFormatterOrdinalStyle,
 NSNumberFormatterCurrencyISOCodeStyle NS_ENUM_AVAILABLE(10_11, 9_0) = kCFNumberFormatterCurrencyISOCodeStyle,
 NSNumberFormatterCurrencyPluralStyle NS_ENUM_AVAILABLE(10_11, 9_0) = kCFNumberFormatterCurrencyPluralStyle,
 NSNumberFormatterCurrencyAccountingStyle NS_ENUM_AVAILABLE(10_11, 9_0) = kCFNumberFormatterCurrencyAccountingStyle,
 };

２、通过一个格式字符串自定义格式

NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];
[numberFormatter setPositiveFormat:@"###0.##"];
NSString *formattedNumberString = [numberFormatter stringFromNumber:@122344.4563];
NSLog(@"formattedNumberString: %@", formattedNumberString);
// Output for locale en_US: "formattedNumberString: formattedNumberString: 122,344.45"