Sharing image and text using objective c native code

I am trying to share image and text on any selected social media. I want to implement functionality similar to intent sharing in android.

For this I have written following code in objective c and call same method in my unity c# code

 @implementation ViewController
 -(void) shareMethod: (const char *) path
 {
     NSLog(@"Sample Method Execute");
     NSString *imagePath = [NSString stringWithUTF8String:path];
  
     //        UIImage *image      = [UIImage imageNamed:imagePath];
     NSString *message   = @"Best image from my application.";
  
     NSArray *postItems  = @[message];
  
     UIActivityViewController *activityVc = [[UIActivityViewController alloc]initWithActivityItems:postItems applicationActivities:nil];
     [self presentViewController:activityVc animated:YES completion:nil];
 }
 @end
 extern "C"{
     void sampleMethod(const char * path){
         ViewController *vc = [[ViewController alloc] init];
         [vc shareMethod: path];
         [vc release];
     }
 }

But using above code I am getting following warnings in xcode

 2014-11-20 21:04:54.565 screenshotdemo[3731:a0b] Sample Method Execute
 2014-11-20 21:04:54.566 screenshotdemo[3731:a0b] Warning: Attempt to present <UIActivityViewController: 0x16c56f90> on <ViewController: 0xc8e6db0> whose view is not in the window hierarchy!

Also I want to mention that all NSLog statement printed on screen. If I execute same code in core xcode project then it works perfectly but exporting same thing using Unity creates problem for me.

I am facing this problem from many days. Please I need some help to solve the problem.