Share text in wechat with UIDocumentInteraction in iphone sdk

How can we share text in wechat with UIDocumentInteraction controller or UIActivityViewController? I am using this but not succeeded :

UIDocumentInteraction *docController = [UIDocumentInteractionController interactionControllerWithURL:fileURL]; self.docController.delegate = self;

docController.UTI = @"Public Text";

    NSString * msg = @"Hello WEChat";
    NSString * urlWhats = [NSString stringWithFormat:@"%@",msg];
    //controller.UTI = urlWhats;

    docController.annotation = [NSDictionary dictionaryWithObject:@"This is testing" forKey:@"Public Text"];