create #251 demo

Author: xdd666t

example/lib/demo/issue251_tag.dart

@@ -0,0 +1,61 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_smart_dialog/flutter_smart_dialog.dart';
+
+void main() {
+  runApp(MaterialApp(
+    navigatorObservers: [FlutterSmartDialog.observer],
+    builder: FlutterSmartDialog.init(),
+    home: const MyApp(),
+  ));
+}
+
+class MyApp extends StatelessWidget {
+  const MyApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text("Test"),
+      ),
+      body: Center(
+        child: Builder(builder: (ctx) {
+          return ElevatedButton(
+            onPressed: () => show(ctx),
+            child: const Text("Click"),
+          );
+        }),
+      ),
+    );
+  }
+
+  show(BuildContext context) {
+    SmartDialog.showAttach(
+      targetContext: context,
+      alignment: Alignment.topCenter,
+      maskColor: Colors.transparent,
+      usePenetrate: true,
+      keepSingle: true,
+      tag: "tag2",
+      animationType: SmartAnimationType.scale,
+      builder: (_) {
+        return Container(
+          height: 300,
+          width: 500,
+          decoration: BoxDecoration(
+            borderRadius: BorderRadius.circular(20),
+            color: Colors.white,
+          ),
+          alignment: Alignment.center,
+          child: ElevatedButton(
+            onPressed: () {
+              final checkMsg = SmartDialog.checkExist(tag: "tag2").toString();
+              SmartDialog.showToast(checkMsg);
+            },
+            child: const Text('check tag status'),
+          ),
+        );
+      },
+    );
+  }
+}