大家都知道，Extension是需要Host App（宿主应用）来唤起的。比如微信的分享扩展就可以在照片应用和Safari上唤起。 那我们如何在自己的应用内唤起微信呢？其实别人家14年都写了的文章了。http://indiestack.com/2014/11/share-extension-iterations/
UIActivityViewController
http://nshipster.com/uiactivityviewcontroller/
我们得先来看看UIActivityViewController，我们在Safari看到的分享面板就是这玩意儿咯。唤起share extension 都是通过UIActivityViewController。
image.png
SLComposeViewController
这个是微信Share Extension弹框的VC。 这个类composeViewControllerForServiceType的方法，通过名字直接拿到对应VC。微信分享组件的名字不方便透露，大家可以通过对UIActivityViewController回调方法的研究拿到。
NSString* serviceName = @"........";
SLComposeViewController* myController = [SLComposeViewController composeViewControllerForServiceType:serviceName];
[myController setInitialText:@"Hello World"];
[[self navigationController] presentViewController:myController animated:YES completion:nil];";
SLComposeViewController* myController = [SLComposeViewController composeViewControllerForServiceType:serviceName];
[myController setInitialText:@"Hello World"];
[[self navigationController] presentViewController:myController animated:YES completion:nil];
用下面两个方法，带上自己的图片或者url。
// Adds an image to the post. Returns NO if the additional image will not fit
// within the character space currently available, or if the sheet has already
// been presented to the user.
- (BOOL)addImage:(UIImage *)image;
// Adds a URL to the post. Returns NO if the additional URL will not fit
// within the character space currently available, or if the sheet has already
// been presented to the user.
- (BOOL)addURL:(NSURL *)url;
