iOS 字符串转UTF-8

- (NSString*)encodeValue:(NSString*)value
{
    NSString* encodedValue = value;
    if (value.length > 0) {
        encodedValue = (__bridge_transfer  NSString*)CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault, (__bridge CFStringRef)value, NULL, (__bridge CFStringRef)@"!*'();:@&=+$,/?%#[]", kCFStringEncodingUTF8 );
    }
    return encodedValue;
}