Google Android - это несложно

Код: Выделить всё

private void btnLoadAvatar_Click(object sender, EventArgs e)
        {
            //Intent = new Intent();
            //Intent.SetType("image/*");
            //Intent.SetAction(Intent.ActionGetContent);
            
            //StartActivityForResult(Intent.CreateChooser(Intent, "Select Picture"), pickImageId);

            Intent intent = new Intent();
            intent.SetType("image/*");
            intent.SetAction(Intent.ActionGetContent);
            StartActivityForResult(Intent.CreateChooser(
                intent,
                "Select Picture"),
                pickImageId);
        }

        protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
        {
            if ((requestCode == pickImageId) && (resultCode == Result.Ok) && (data != null))
            {
                Android.Net.Uri uri = data.Data;
                ivAvatar.SetImageURI(uri);
                UploadImage(GetPathToImage(uri));
            }
        }