Intent intent = new Intent(Intent.ActionGetContent);

            intent.AddCategory(Intent.CategoryOpenable);

            intent.SetType("file/*");

            StartActivityForResult(Intent.CreateChooser(intent, "选择备份文件"), );

protected override void OnActivityResult(int requestCode, [GeneratedEnum] Result resultCode, Intent data)

        {

            if (requestCode == )

            {

                var uri = data.Data as Android.Net.Uri;

                var filepath = uri.Path;

            }

            base.OnActivityResult(requestCode, resultCode, data);

        }