iOS Category重写系统方法

写了个分类使用方法交换
iOS里面字符串转URL的时候里面有中文就会失败为nil，全部转换可能会出问题，有#这种转换后打不开。想统一处理，使用Category重写系统方法，原来使用URLWithString的会直接使用新的方法转换成功就继续，转换失败就转义中文后再试。

上代码.m文件如下：

#import "NSURL+XXX.h"

@implementation NSURL (XXX)

+(void)load
{
   Method methodOld = class_getClassMethod([self class], @selector(URLWithString:));
   Method methodNew = class_getClassMethod([self class], @selector(URLWithCHString:));
   method_exchangeImplementations(methodOld, methodNew);
}


+(NSURL *)URLWithCHString:(NSString *)URLString
{
   NSURL *url = [NSURL URLWithCHString:URLString];
   if (url) {
       return url;
   }else{
       NSString *str = [NSURL urlEncodeChineseString:URLString];
       NSURL *urlCH = [NSURL URLWithCHString:str];
       return urlCH;
   }
}


//字符串转换只转码中文，不统一转换#等特殊字符会出问题
+ (NSString *)urlEncodeChineseString:(NSString *)string
{
   //(unicode中文编码范围是0x4e00~0x9fa5)
   for (int i = 0; i < string.length; i++) {
       int utfCode = 0;
       void *buffer = &utfCode;
       NSRange range = NSMakeRange(i, 1);
       BOOL b = [string getBytes:buffer maxLength:2 usedLength:NULL encoding:NSUTF16LittleEndianStringEncoding options:NSStringEncodingConversionExternalRepresentation range:range remainingRange:NULL];
       if (b && (utfCode >= 0x4e00 && utfCode <= 0x9fa5)) {
           NSString*bStr = [string substringWithRange:NSMakeRange(i,1)];//识别汉字
           NSString *chineseStr = [bStr stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];//转化
           string = [string stringByReplacingOccurrencesOfString:bStr withString:chineseStr];//替换
       }
   }
   return string;
}
@end