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Share to social media on iOS with UIActivityViewController

From UIViewController to screenshot to social media.

Send your shares into space. Source: Oliver K. Ernst (author). License: Attribution-NonCommercial-NoDerivatives 4.0 International

The problem:

You want to implement a share button that takes a screenshot from your app and let’s users share it to social media.

Caveats:

  • You want to create a custom image by creating a custom UIViewController.
  • You don’t want the UIViewController to show.
  • You want to show a nice preview of the image that you’ll share.

You cant find the complete project on GitHub here.

Let’s get started with a clean project.

Project setup

Let’s start with a clean project. Add a share button to the default view controller. For the button image, you can choose square.and.arrow.up to make it look like a native share button.

Add a new view controller which will produce the image to be shared. Do not add a segue from the old view controller to the new one — this will be done programmatically.

Change it’s size to be a custom value in the Size inspector by selecting Freeform and entering the size.

Also make sure you uncheck Resize View From Nib in the Attributes inspector.

Else the custom size will not appear when we instantiate the view controllor.

Add a new class for this view controller called ShareViewController and assign it in the storyboard. Also give it the Storyboard ID: shareVC .

You can add whatever you want to the view controller.

Taking the screenshot

First, let’s make a simple implementation for the ShareViewController :

It updates the message field, and provides a simple populate method for that task (very important if you have non-trivial data types to separate the GUI and logic!).

The most important method is the one that takes the screenshot — without showing the ShareViewController :

  • First, instantiate the view controller. You don’t need to push it to the navigation controller, since we don’t want to show it.
  • Next, begin taking the screenshot with UIGraphicsBeginImageContextWithOptions . Pass the vc.view.frame.size such that it uses the same size as the ShareViewController . The 3.0 factor is a scaling factor to increase the quality of the image — you will need to dial this in depending on the size of your ShareViewController .
  • Next, populate the ShareViewController with the data.
  • Render the image with vc.view.layer.render(in: UIGraphicsGetCurrentContext()!) . This creates the screenshot from the view controller without showing it.
  • Finally, create an image from the context and return it. Don’t forget to call UIGraphicsEndImageContext!

Sharing to social media

Next, in the main ViewController , hook up a short method to the share button:

Here, share is implemented as follows:

  • First we take the screenshot, obtaining a UIImage using the take_screen_shot method.
  • Next we set the filename. Note that this is also visible to the user in the activity view controller. Every time the user shares, this image will be overwritten — so it is not taking up too much space on the phone.
  • Next store the image and get it’s URL.
  • Create the UIActivityViewController , passing the URL to share.
  • Set the excluded activities — there’s lots to choose from here, but probably you don’t want the reading list option.
  • Finally, present the view controller.

We already did the screen shot method. Next, the save image method:

which should be self-explanatory.

The only missing method is the error message:

This, too, should be self-explanatory.

Result

Let’s see how it turned out — pressing the button gives:

As we can see, there’s a preview of the image we’re sharing. The image is:

Final thoughts

Note that not all of the buttons may work correctly. For example, if you choose Save Image , you may get:

This app has crashed because it attempted to access privacy-sensitive data without a usage description.  The app's Info.plist must contain an NSPhotoLibraryAddUsageDescription key with a string value explaining to the user how the app uses this data.

So… do that!

You cant find the complete project on GitHub here.

Happy sharing!

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A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
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Oliver K. Ernst, Ph.D.

Oliver K. Ernst, Ph.D.

Coding, ML, AI — oliver-ernst.com

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