feat return a boolean indicating whether the [data] was successfully …

…sent using the [shareData] method

doc improve documentation form [shareData] method

feat return the original Future from the [disposeOverlayListener] method

lib/src/overlay_window.dart

@@ -81,9 +81,24 @@ class FlutterOverlayWindow {
     return _res;
   }
 
-  /// Broadcast data to and from overlay app
-  static Future shareData(dynamic data) async {
-    return await _overlayMessageChannel.send(data);
+  /// Broadcast [data] to and from overlay app.
+  ///
+  /// If `true` is returned, it indicates that the [data] was sent. However, it does not guarantee
+  /// that the [data] has arrived at its destination,
+  /// i.e. to the listeners of the [overlayListener] stream.
+  /// Typically, success in sending should imply successful delivery.
+  ///
+  /// If `false` is returned, it means that there is no registered message channel to handle
+  /// sending this [data], and thus, the [data] was not sent.
+  ///
+  /// This method may return `false` under the following conditions:
+  /// - The overlay is closed.
+  /// - The application is detached from the activity, i.e. the application is closed.
+  ///
+  /// Returns `true` if the [data] was sent successfully, otherwise `false`.
+  static Future<bool> shareData(dynamic data) async {
+    final isSent = await _overlayMessageChannel.send(data);
+    return isSent as bool;
   }
 
   /// Streams message shared between overlay and main app
@@ -123,7 +138,7 @@ class FlutterOverlayWindow {
   /// Dispose overlay stream.
   ///
   /// Once disposed, only a complete restart of the application will re-initialize the listener.
-  static void disposeOverlayListener() {
-    _controller.close();
+  static Future<dynamic> disposeOverlayListener() {
+    return _controller.close();
   }
 }