fix(example): fix use_build_context_synchronously warning in the example

Author: ThibaultBee

example/lib/main.dart

@@ -103,15 +103,21 @@ class UploaderPageState extends State<UploaderPage> {
                     });
                     log("VideoId : ${video.videoId}");
                     log("Title : ${video.title}");
-                    showSuccessSnackBar(
-                        context, "Video ${video.videoId} uploaded");
+                    if (context.mounted) {
+                      showSuccessSnackBar(
+                          context, "Video ${video.videoId} uploaded");
+                    }
                   } on Exception catch (e) {
                     log("Failed to upload video: $e");
-                    showErrorSnackBar(
-                        context, "Failed to upload video: ${e.message}");
+                    if (context.mounted) {
+                      showErrorSnackBar(
+                          context, "Failed to upload video: ${e.message}");
+                    }
                   } catch (e) {
                     log("Failed to upload video: $e");
-                    showErrorSnackBar(context, "Failed to upload video $e");
+                    if (context.mounted) {
+                      showErrorSnackBar(context, "Failed to upload video $e");
+                    }
                   }
                 }
               },
@@ -147,21 +153,32 @@ class UploaderPageState extends State<UploaderPage> {
   }
 
   void showSuccessSnackBar(BuildContext context, String message) {
-    showSnackBar(context, message, backgroundColor: Colors.green);
+    context.showSnackBar(message, backgroundColor: Colors.green);
   }
 
   void showErrorSnackBar(BuildContext context, String message) {
-    showSnackBar(context, message,
+    context.showSnackBar(message,
         backgroundColor: Colors.red,
         duration: const Duration(seconds: 60),
         showCloseIcon: true);
   }
+}
+
+extension ErrorExtension on Exception {
+  String get message {
+    if (this is PlatformException) {
+      return (this as PlatformException).message ?? "Unknown error";
+    }
+    return toString();
+  }
+}
 
-  void showSnackBar(BuildContext context, String message,
+extension BuildContextSnachBarExtension on BuildContext {
+  void showSnackBar(String message,
       {Color? backgroundColor,
       Duration duration = const Duration(seconds: 4),
       bool showCloseIcon = false}) {
-    ScaffoldMessenger.of(context).showSnackBar(
+    ScaffoldMessenger.of(this).showSnackBar(
       SnackBar(
         content: Text(message),
         backgroundColor: backgroundColor,
@@ -171,12 +188,3 @@ class UploaderPageState extends State<UploaderPage> {
     );
   }
 }
-
-extension ErrorExtension on Exception {
-  String get message {
-    if (this is PlatformException) {
-      return (this as PlatformException).message ?? "Unknown error";
-    }
-    return toString();
-  }
-}