Sharing an image via ActivityViewController with iOS and Unity3D

Welcome to my tutorial on how to share a screen image on an iOS device by extending our Unity Plugin.

We will add a share function to our plugin code that will make use of the standard iOS ActivityViewController. Using this View Controller is quite complex and powerful, and will require a setup that is dependent on the device being used.

Once again this tutorial assumes a reasonable familiarity with unity, C sharp, objective-c, iOS programming and XCode.

Let’s get started by loading up our previous project in Unity and adding a share button to the scene.

In the Hierarchy view, click ‘Create’ and select UI->Button. This will create a Canvas and add a button directly to it.

Select the button, adjust it’s anchor to be top-center and set the Y pos to -15, which should put the top of the button against the top of the screen.

Expand the button in the hierarchy and click on Text and change the text string to ‘Share’.

Now double click our PluginTest script to open it up in Visual Studio so we can add the C# share function.

First, let’s add the reference to the external IOS method that we’ll use. In the section with our other extern declarations, add the following two lines:

 private static extern void IOSshareScreenImage(byte[] imagePNG, long imageLen, string caption, intCallback callback);

We’re going to need a public reference to our UI button. So add the line

 public Button shareButton;

We’ll also need to add the appropriate Using statement, so you can right click on Button, select Quick Fix and then ‘using UnityEngine.UI;’.

Comment out the line in our Start method that randomly shows the alert dialog. We’ll use the alert dialog to let the user know when the share method is finished along with the completion result later.

Let’s add the method that our Button will hook into. This method will call into another method that will actually create the screenshot and share it. To make our screenshot clean, we’ll hide the button before we take the screenshot and then restore it when the screenshot has been shared.

//called when the user taps the 'share' button
public void ShareScreenTapped()
  if (shareButton != null)
  ShareScreenShot(Application.productName + " screenshot", (int result) =>;
      Debug.Log("share completed with: " + result);
      CreateIOSAlert(new string[] { "Share Complete", "Share completed with result " + result, "Ok" });
      if (shareButton != null)

We’re using an anonymous function that will be called when the share function completes. This lets us re-enable the button and pop-up an alert view with the result from the share function.

This next section is quite complex. It involves saving off a reference to the passed function, a callback function that will receive the success/fail status from the iOS ActivityShare function, a method to take the screenshot and then a co-routine to wait for the end of the frame before grabbing a copy of the frame buffer and passing it to our iOS method as a PNG.

First, let’s create two static variables. One to hold the passed function reference:

static System.Action ShareCompleteAction;

And one to hold a bool state that will be true while we’re sharing a screenshot:

static bool isSharingScreenShot;

This is to prevent the method being called while we’re waiting for a previous call to complete.
Now we’ll add the callback function that will be called from iOS. In order to do that, we need to mark it with MonoPInvokeCallback so the compiler knows to marshal the call correctly.

static void shareCallBack(int result)
  Debug.Log("Unity: share completed with result: " + result);
  if (ShareCompleteAction != null)
  isSharingScreenShot = false;

This is similar to the callback function used by the AlertView, and in fact uses the same intCallback type. When this function is called, it will trigger the stored reference to the function passed into ShareScreenShot, if it’s not null, and clear the isSharingScreenShot flag as we’re finished.

We’re now ready to add the ShareScreenShot method. This method will make sure we’re not already sharing a screenshot and then start a co-routine that will create a texture containing the current frame buffer. As recommended by Unity, we’ll wait for the end of the next frame to ensure the frame buffer is fully rendered. Add the following lines:

public void ShareScreenShot(string caption, System.Action shareComplete)
  if (isSharingScreenShot)
    Debug.LogError("Already sharing screenshot - aborting");
  isSharingScreenShot = true;
  ShareCompleteAction = shareComplete;

  //grab the screenshot & send it to iOS

The co-routine will wait for the end of the next frame and then send the texture we create to our iOS method. Add the following lines to complete our C# modifications:

IEnumerator waitForEndOfFrame(string caption)
  yield return new WaitForEndOfFrame();
  Texture2D image = ScreenCapture.CaptureScreenshotAsTexture();
  Debug.Log("Image size: " + image.width + " x " + image.height);
  byte[] imagePNG = image.EncodeToPNG();
  Debug.Log("png size: " + imagePNG.Length);
  if (Application.platform == RuntimePlatform.IPhonePlayer)
    IOSshareScreenImage(imagePNG, imagePNG.Length, caption, shareCallBack);

After waiting until the end of frame, we grab the frame buffer into a 2D texture. From this, we construct a PNG rendition of the image, and then after ensuring we’re on an iOS platform, call into the iOS method, passing the PNG, it’s length, the caption and a pointer to our shareCallBack function.

With the C# modifications completed, we need to hook up our button and also set the reference to it for our script. I had to adjust my Unity layout so you could see how I connected the button to the ShareScreenTapped method.

Now it’s time to update our iOS code. Double click the file ‘MyPlugin’ in the Plugins/iOS folder. This will launch XCode and open our file.

First, add a method to the MyPlugin class that will package the PNG image and caption into an NSArray and pass them to an ActivityViewController.
Before we do that, we need to add a few extra variables to our class. In the @interface declaration at the top of the file add these two lines:

INT_CALLBACK shareCallBack;
UIPopoverController *popover;

The shareCallBack variable will hold the pointer to our C# callback function, while the popover variable will point to the popover controller we’ll use if the code is running on an iPad device.

With that done, we can add the method’s we’ll need to the main class by adding the following lines before the @end statement for the MyPlugin @implementation:

-(void) shareScreenImage:(const unsigned char*) imagePNG_in length:(long)length caption:(const char*) caption_in callback:(INT_CALLBACK) callback
  NSMutableArray *shareableItems = [NSMutableArray arrayWithCapacity:2];
  //This array will hold the caption and image so we can send it to the share activity.
  NSString *caption;
  UIImage *image;
  if (caption_in!=nil)
      caption = [MyPlugin createNSString:caption_in];
      [shareableItems addObject:caption];
  if (imagePNG_in!=nil)
      NSData* pngData = [NSData dataWithBytes:imagePNG_in length:length];
      image = [UIImage imageWithData:pngData];
      [shareableItems addObject:image];
      pngData = nil;

This will convert the caption, if it’s set, to an NSString and the PNG data to a UIImage. Note we have to first convert the supplied byte array into a NSData object, and we need the length of the array to achieve this.

shareCallBack = callback;
UIActivityViewController *activityViewController = [[UIActivityViewController alloc] initWithActivityItems:shareableItems applicationActivities:nil];
activityViewController.completionWithItemsHandler = ^(NSString *activityType, BOOL completed, NSArray *returnedItems, NSError *activityError) {
    NSLog(@"Activity %@ completed: %d",activityType,completed);
    if (activityError!=nil)
        NSLog(@"Error: %@",[activityError localizedDescription]);
    if (shareCallBack!=nil)

Here we create a UIActivityViewController with the shareableItems array we setup and populated earlier. We also construct a completionWithItemsHandler. This function will be called when the user completes the share function, either by selecting a method, or by cancelling the request.

The completion function will pass the completed bool to our callback method, assuming it’s not nil.

if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone)
    [UnityGetGLViewController() presentViewController:activityViewController animated:YES completion:^{
        NSLog(@"share presented");
    popover = [[UIPopoverController alloc] initWithContentViewController:activityViewController];
    UIView *mainView = UnityGetGLView();
    popover.delegate = nil;
    [popover presentPopoverFromRect:CGRectMake(mainView.frame.size.width/2, mainView.frame.size.height-10, 0, 0) inView:mainView permittedArrowDirections:UIPopoverArrowDirectionAny animated:YES];

In order to present the activity view controller, we need to use two different methods, one for iPhone devices and another using a popover controller for iPad devices. We’ll make the choice by checking the result of the macro UI_USER_INTERFACE_IDIOM.

On iPhone devices, we can present the ViewController using the main Unity ViewController directly, while on iPad devices, we first create a popover controller and then use the main Unity View as the parent view to present the popover.

In both cases, the ActivityViewController finish method is used to notify Unity that the share is complete via our supplied callback function.

Finally, we need to add a C style method that our C# code will call into, which will call our new share method on the plugin. Add the following lines to the extern C block:

void IOSshareScreenImage(const unsigned char* imagePNG, long imageLen, const char* caption, INT_CALLBACK callback)
    [[MyPlugin sharedInstance] shareScreenImage:imagePNG length:imageLen caption:caption callback:callback];

This completes the iOS code modifications, however we need to add a key to the application’s plist file that let’s iOS know we may want to save screenshots into the user’s camera roll.

Click on the Info.plist file in the file hierarchy in Xcode, and then click the + icon to the right of the first line. In the text box that pops up, type the following:

Privacy - Photo Library Additions Usage Description

And then in the string box to the right, add a description that a user might see when they try to save a screenshot. I used:

Allow access to save screenshots

With all these modifications in place, we’re ready to build and test the code. Switch back to Unity, give it a few seconds to rebuild the C# code and then press CMD-B to start the project building.

Once XCode has finished building the project the code will execute on our simulator. Tap the ‘share’ button at the top of the screen and you’ll see the activity controller appear. You can then select what iOS will do with your image.

Go back to XCode and select an iPad as a target device. Now when you run the code and tap the share button, you’ll see a popover appear with the share activities in it. Unity continues to run behind this popover as you’d expect.

Both types of device will display an alert when the share is completed with the bool completion status. A 0 indicates the share failed, while a 1 indicates success.

If you run on a real device, then you’ll get more share options, including iMessage and Facebook if you have the app installed. If you use iMessage, along with the screenshot image you’ll see the caption text we’ve passed through. Notice that the screenshot doesn’t have our ‘share’ button on it, as we hid that before we grabbed the frame buffer.

We’ve now added a share function to Unity that allows the user to send a screenshot to various activities on their device without leaving your App. Use this to let users send highscore images, or new level images to their friends.

I hope you found this tutorial useful and are able to use it to add sharing to your apps. The code for this plugin can be found at and the video at

As always, please feel free to reach out with any comments or questions.

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