如何将字符串转化成二进制流的字符串了？

如何将字符串转化成二进制流的字符串了？

---

NSString *str = self.searchBar.text; //需要转化的字符串
 NSString * encodedString = (NSString *)CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes( kCFAllocatorDefault, (CFStringRef)str, NULL, NULL,  kCFStringEncodingUTF8 ));