Xamarin.Forms App return data to calling App

Question

So, either I am asking incorrectly, or it isn't possible, let's see which...

If my app (Xamarin.Forms) is launched from another app, in order to get a url from my app, how do I return that data to the calling app? I wrongly assumed SetResult and Finish, I also wrongly assumed StartActivityForResult, but there has to be a way to do this. I know how to get data INTO my app from another app, but not the same in return.

POSSIBLE PARTIAL SOLUTION -- UPDATE, FAILS

So I have to setup an interface in my PCL, and call the method from the listview item selected handler, in the Android app I can then do this:

Intent result = new Intent("com.example.RESULT_ACTION", Uri.parse("content://result_url"));
setResult(Activity.RESULT_OK, result);
finish();

(source: https://developer.android.com/training/basics/intents/filters.html)

Is this looking right, and how would I implement the same thing on iOS?

END

I deleted my previous question because I couldn't explain the problem clearly, so here goes.

I have a Xamarin Forms app, I want to use a section of this app as a gallery. Currently I have images displayed in a list, and I have an Intent filter set that launches this page when you select the app as the source for an image (such as upload image on Facebook).
My issue is that I don't know how to return the data (the selected image) back to the app / webpage that made the request. In android I understand that you would use StartActivityForResult and OnActivityResult to handle this, but I am using Xamarin Forms (Android, iOS, UWP) and can't really find a solution that could be used cross-platform.

Just a link to documentation that covers this would be great, but if you have an example then even better.

Thanks

EDIT

Here is the code used to launch the app, I am interested in getting data back from the Intent.ActionPick after the user has selected an image from a ListView, which is in a ContentPage in the PCL.

[Activity(Label = "", Icon = "@drawable/icon", Theme = "@style/DefaultTheme", MainLauncher = true, LaunchMode = LaunchMode.SingleTop,
          ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation)]
[IntentFilter(new[] { Intent.ActionSend }, Categories = new[] { Intent.CategoryDefault }, DataMimeType = @"*/*")]
[IntentFilter(new[] { Intent.ActionView, Intent.ActionPick, Intent.ActionGetContent }, Categories = new[] { Intent.CategoryDefault, Intent.CategoryOpenable }, DataMimeType = @"*/*")]
public class MainActivity : FormsAppCompatActivity
{
    protected override void OnCreate(Bundle bundle)
    {
        try
        {
            base.OnCreate(bundle);

            CurrentPlatform.Init();
            Xamarin.Forms.Forms.Init(this, bundle);

            App _app = new App();
            LoadApplication(_app);

            if (Intent.Action == Intent.ActionSend)
            {
                var image = Intent.ClipData.GetItemAt(0);
                var imageStream = ContentResolver.OpenInputStream(image.Uri);
                var memOfImage = new System.IO.MemoryStream();
                imageStream.CopyTo(memOfImage);
                _app.UploadManager(memOfImage.ToArray());  //This allows me to upload images to my app
            }
            else if (Intent.Action == Intent.ActionPick)
            {
                _app.SelectManager(); //here is where I need help
            }
            else
            {
                _app.AuthManager(); //this is the default route
            }
        }
        catch (Exception e)
        {
        }
    }

Answer 1

You can use static public class to save and access results like:

public static class StaticClass
{
     public static int Result;
}

Answer 2

It seems you cannot use remote URI to provide to calling app. Some posts I checked suggest to store the file locally and provide it's path to calling app. To avoid memory leak with many files stored I suggest to use the same file name then you will have only one file at any moment.

One more note. I tested this solution in facebook. Skype doesn't seem to accept that and, again, the posts I checked saying that Skype doesn't handle Intent properly (not sure what that means).

Now to solution. In main activity for example in OnCreate method add the follow. ReturnImagePage is the name of my page class where I select an image

        Xamarin.Forms.MessagingCenter.Subscribe<ReturnImagePage, string>(this, "imageUri", (sender, requestedUri) => {

            Intent share = new Intent();
            string uri = "file://" + requestedUri;
            share.SetData(Android.Net.Uri.Parse(uri));

            // OR
            //Android.Net.Uri uri = Android.Net.Uri.Parse(requestedUri);
            //Intent share = new Intent(Intent.ActionSend);
            //share.PutExtra(Intent.ExtraStream, uri);
            //share.SetType("image/*");
            //share.AddFlags(ActivityFlags.GrantReadUriPermission);

            SetResult(Result.Ok, share);
            Finish();
        });

Above will listen for the message when the image is selected.

Then in XFroms code when image is selected dowload it, store it, get path and send to Activity using it's path. Below is my test path

MessagingCenter.Send<ReturnImagePage, string>(this, "imageUri", "/storage/emulated/0/Android/data/ButtonRendererDemo.Droid/files/Pictures/temp/IMG_20170207_174559_21.jpg");