Daniel Hindrikes

This blog post will show you how to build a screenshot manager to use from shared code when building apps with Xamarin for Windows Phone, Android and iOS.

First of all we need to create an interface in the shared code library. In this example there will be one method in the screenshot manager. This method will capture the screen and return a byte array that you for example can save to a server.

 public interface IScreenshotManager
 {
        Task CaptureAsync();
 }

All platforms that we will target capture the screen in different ways. Therefor will each platform have a own implementation of the interface. If you register the interface with a platform specific implementation for each platform you can call the ScreenshotManager from shared code.

Windows Phone
For Windows Phone you need to render the root frame into a WritableBitmap.

public class ScreenshotManager : IScreenshotManager
    {
        public async Task CaptureAsync()
        {
            var rootFrame = Application.Current.RootVisual as PhoneApplicationFrame;

            var screenImage = new WriteableBitmap((int)rootFrame.ActualWidth, (int)rootFrame.ActualHeight);
            screenImage.Render(rootFrame, new MatrixTransform());
            screenImage.Invalidate();

            using (var stream = new MemoryStream())
            {
                screenImage.SaveJpeg(stream, screenImage.PixelWidth, screenImage.PixelHeight, 0, 100);
                var bytes = stream.ToArray();
                return bytes;
            }
        }
    }

iOS
For iOS you need the view from the RootViewController to create a screenshot from. This code will work for iOS7 and above.

public class ScreenshotManager : IScreenshotManager
    {
        public async System.Threading.Tasks.Task CaptureAsync()
        {
            var view = UIApplication.SharedApplication.KeyWindow.RootViewController.View;
           
            UIGraphics.BeginImageContext(view.Frame.Size);
            view.DrawViewHierarchy(view.Frame, true);
            var image = UIGraphics.GetImageFromCurrentImageContext();
            UIGraphics.EndImageContext();

            using(var imageData = image.AsPNG())
            {
                var bytes = new byte[imageData.Length];
                System.Runtime.InteropServices.Marshal.Copy(imageData.Bytes, bytes, 0, Convert.ToInt32(imageData.Length));
                return bytes;
            }
           
        }
    }

Android
To create a screenshot in Android you need to have access to a activity. The easiest way to access a activity is to create a static method on the ScreenshotManager that you setting before using the ScreenshotManager.

public class ScreenshotManager : IScreenshotManager
    {
        public static Activity Activity { get; set; }

        public async System.Threading.Tasks.Task CaptureAsync()
        {
            if(Activity == null)
            {
                throw new Exception("You have to set ScreenshotManager.Activity in your Android project");
            }

            var view = Activity.Window.DecorView;
            view.DrawingCacheEnabled = true;

            Bitmap bitmap = view.GetDrawingCache(true);

            byte[] bitmapData;

            using (var stream = new MemoryStream())
            {
                bitmap.Compress(Bitmap.CompressFormat.Png, 0, stream);
                bitmapData = stream.ToArray();
            }

            return bitmapData;
        }
    }