1.OC中对中文编码
NSString *city = @"成都";
//正确编码为: %e6%88%90%e9%83%bd
最新方法：
方法一：
NSString *charactersToEscape = @"?!@#$^&%*+,:;='\"`<>()[]{}/\\| ";
NSCharacterSet *allowedCharacters = [[NSCharacterSet characterSetWithCharactersInString:charactersToEscape] invertedSet];
方法二：
NSCharacterSet *allowedCharacters = [NSCharacterSet URLQueryAllowedCharacterSet]
NSString *city_encode = [city stringByAddingPercentEncodingWithAllowedCharacters:allowedCharacters];
已废弃方法：
NSString *city_encode = [city stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
对中文、特殊符号 & % 和空格 都必须转译才能正确访问，一般需要转译的字符:@”?!@#$^&%*+,:;=’\”`<>()[]{}/\| “
2.Unicode和汉字互转
iOS9-
//unicode转中文
NSString* strA = [@"%E4%B8%AD%E5%9B%BD"stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
//中文转unicode
NSString *strB = [@"中国"stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
ios9+
//中文转unicode
urlStr = [@"url地址" stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];
//unicode转中文
urlStr = [@"url地址" stringByRemovingPercentEncoding];
3.区别stringByAdding… 和stringByReplacing…
...Adding...
将Unicode字符转换成有百分号的形式;
对中文和一些特殊字符进行编码;
...Adding...
将百分号形式转换成Unicode形式
