Making screen capture in xamarin.forms

Check out this blog post by Daniel Hindrikes.

I'm going to assume that you use a PCL for your shared code.

You will need to create an interface in your PCL. He calls it IScreenshotManager. The declaration looks like this:

public interface IScreenshotManager
{
   Task<byte[]> CaptureAsync();
}

Now all platforms will have their own implementation for it. For iOS;

public class ScreenshotManager : IScreenshotManager
{
    public async System.Threading.Tasks.Task<byte[]> 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;
        }

    }
}

For Android:

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

    public async System.Threading.Tasks.Task<byte[]> 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;
    }
}

And for Windows Phone:

public class ScreenshotManager : IScreenshotManager
{
    public async Task<byte[]> 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;
        }
    }
}

Don't forget to register your platform specific implementations with the attribute which registers it with the Dependency Service, like this:

[assembly: Xamarin.Forms.Dependency (typeof (ScreenshotManager))]

It goes above the namespace declaration.

Now from your shared code you would be able to get the byte[] of a screenshot with a call like this:

var screenshotBytes = DependencyService.Get<IScreenshotManager>().CaptureAsync();

You probably want to check if DependencyService.Get<IScreenshotManager>() isn't null before using it.

After that you can turn your byte[] into an image and do whatever you like with it!

Implementation for UWP

public async Task<byte[]> CaptureAsync()
{
    //create and capture Window
    var renderTargetBitmap = new RenderTargetBitmap();
    await renderTargetBitmap.RenderAsync(Window.Current.Content);

    var pixelpuffer = await renderTargetBitmap.GetPixelsAsync();
    var logicalDpi = DisplayInformation.GetForCurrentView().LogicalDpi;

    IRandomAccessStream stream = new InMemoryRandomAccessStream();
    BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.PngEncoderId, stream);
    encoder.BitmapTransform.InterpolationMode = BitmapInterpolationMode.Fant;
    encoder.SetPixelData(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Straight, (uint)renderTargetBitmap.PixelWidth, (uint)renderTargetBitmap.PixelHeight, logicalDpi, logicalDpi, pixelpuffer.ToArray());
    await encoder.FlushAsync();
    byte[] resultingBuffer = new byte[stream.Size];

    await stream.ReadAsync(resultingBuffer.AsBuffer(), (uint)resultingBuffer.Length, InputStreamOptions.None);

    return resultingBuffer;

}