将string转换成UTF8在进行请求

在请求服务器时，如果参数中带有中文字符。就会报参数格式错误，需要将其转换成UTF8

@interface NSString (NSURLUtilities)

/* Adds all percent escapes necessary to convert the receiver into a legal URL string.  Uses the given encoding to determine the correct percent escapes (returning nil if the given encoding cannot encode a particular character).  See CFURLCreateStringByAddingPercentEscapes in CFURL.h for more complex transformations

*/

- (NSString *)stringByAddingPercentEscapesUsingEncoding:(NSStringEncoding)enc;

/* Replaces all percent escapes with the matching characters as determined by the given encoding.  Returns nil if the transformation is not possible (i.e. the percent escapes give a byte sequence not legal in the given encoding).  See CFURLCreateStringByReplacingPercentEscapes in CFURL.h for more complex transformations

*/

- (NSString *)stringByReplacingPercentEscapesUsingEncoding:(NSStringEncoding)enc;

@end

代码如下：

@"keyword": [searchSoft.text stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding],