如何在iphone上解码utf8 NSstring？

NSString *utf8String = @"需要解码的UTF-8字符串";
NSString *decodedString = [utf8String stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

NSString *utf8String = @"需要解码的UTF-8字符串";
NSData *data = [utf8String dataUsingEncoding:NSUTF8StringEncoding];
NSString *decodedString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];