fix: error handler, connection logic

android/src/main/java/id/kalanusa/flutter_zsdk/FlutterZsdkPlugin.java

   private MethodChannel channel;
   private Context context;
   private Activity activity;
-  private ArrayList<BluetoothPrinter> discoveredPrinterList = new ArrayList<BluetoothPrinter>();
   public static final String bluetoothDiscoveryEventChannel = "id.kalanusa.flutter_zsdk.channel_events/bluetooth_discovery";
-  private EventChannel.EventSink attachEvent;
-  private Handler handler;
   private DartExecutor dartExecutor;
   private BinaryMessenger binaryMessenger;
 

android/src/main/java/id/kalanusa/flutter_zsdk/bluetoothconnectionhandler/BluetoothConnectionHandler.java

 import io.flutter.plugin.common.MethodChannel;
 
 public class BluetoothConnectionHandler {
-    String macAddress;
 
     public void handle(@NonNull MethodCall call, @NonNull MethodChannel.Result result) {
 
                     String connectionInfo = BluetoothConnectionHolder.connection.getSimpleConnectionName();
                     String currentConnectionMacAddress = connectionInfo.substring(0, 17);
 
-                    if (currentConnectionMacAddress != macAddressArgument) {
+                    if (!currentConnectionMacAddress.equals(macAddressArgument)) {
                         closeAndReopenConnection(result, macAddressArgument);
 
+                    } else {
+                        openConnection(result);
+
                     }
+
                     break;
                 }
 
         new Thread(new Runnable() {
             @Override
             public void run() {
-                BluetoothConnectionHolder.getSimpleConnectionName();
-                boolean isConnected = BluetoothConnectionHolder.connection.isConnected();
+//                BluetoothConnectionHolder.getSimpleConnectionName();
+                try {
+                    boolean isConnected = BluetoothConnectionHolder.connection.isConnected();
 
-                result.success(isConnected);
+                    result.success(isConnected);
 
-                Log.w("From Native (Android)", "isConnected: " + isConnected);
+                    Log.w("From Native (Android)", "isConnected: " + isConnected);
+                } catch (Exception e) {
+                    Log.w("From Native (Android)", "Cant get connection status");
+                    Log.w("From Native (Android)", e.getClass().toString());
+                    Log.w("From Native (Android)", "is exception nullPointerException: " + (e.getClass() == NullPointerException.class));
+
+                    if (e.getClass() == NullPointerException.class) {
+                        result.error("CONNECTION_HAS_NOT_BEEN_ESTABLISHED", "Cant get connection status, establish connection first", e.getCause());
+                    } else {
+                        result.error("CHECK_CONNECTION_ERROR", "Cant get connection status", e.getMessage());
+                    }
+                }
             }
         }).start();
     }
             public void run() {
                 try {
                     BluetoothConnectionHolder.connection.close();
+                    BluetoothConnectionHolder.connection = null;
                     result.success(null);
                 } catch (ConnectionException e) {
                     Log.w("From Native (Android)", "something went wrong when closing connection");

example/lib/main.dart

     setState(() {});
   }
 
+  Future<void> checkConnectionStatus() async {
+    print('invoked checkConnectionStatus from dart');
+    try{
+      bool isConnected = await _flutterZsdkPlugin.isConnected();
+              
+      print('isConnected from dart: $isConnected');
+    } on FlutterZsdkException catch (e) {
+      inspect(e);
+      showSnackBar(e.message.toString());
+    } catch (e) {
+      inspect(e);
+      showSnackBar('Unexpected error while checking connection status');
+    }
+  }
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
 
             ElevatedButton(
               child: Text('Check connection status'),
-              onPressed: () async {
-                bool isConnected =await _flutterZsdkPlugin.isConnected();
-              
-                print('isConnected from dart: $isConnected');
-              },
+              onPressed: checkConnectionStatus,
             ),
             SizedBox(height: 20),
             

lib/src/flutter_zsdk_method_channel.dart

 import 'package:flutter/services.dart';
 import 'package:flutter_blue_plus/flutter_blue_plus.dart';
 import 'package:flutter_zsdk/src/models/bluetooth_printer.dart';
+import 'package:flutter_zsdk/src/models/error_code.dart';
 import 'package:flutter_zsdk/src/models/flutter_zsdk_exception.dart';
 import 'package:permission_handler/permission_handler.dart';
 
     //   print(event);
     // });
     if (!await FlutterBluePlus.isSupported) {
-      throw FlutterZsdkException("Bluetooth is not supported on this device.");
+      throw FlutterZsdkException(ErrorCode.bluetoothIsNotSupported, "Bluetooth is not supported on this device.");
     }
 
 
         try {
           await FlutterBluePlus.turnOn();
         } on FlutterBluePlusException catch (e) {
-          throw FlutterZsdkException("Failed to turn on bluetooth: ${e.description}");
+          throw FlutterZsdkException(ErrorCode.turnOnBluetoothError, "Failed to turn on bluetooth: ${e.description}");
         }
       } else {
-        throw FlutterZsdkException("Bluetooth is not turned on on this device.");
+        throw FlutterZsdkException(ErrorCode.bluetoothDisabled, "Bluetooth is not turned on on this device.");
       }
     }
 
         return bluetoothDiscoveryEventChannel.receiveBroadcastStream();
       } else {
         // throw Exception("Permissions not granted, please allow permission to discover bluetooth printers.");
-        throw FlutterZsdkException("Permissions not granted, please allow permission to discover bluetooth printers.");
+        throw FlutterZsdkException(ErrorCode.permissionNotGranted, "Permissions not granted, please allow permission to discover bluetooth printers.");
       }
 
     } else {
 
     } on PlatformException catch (e) {
       inspect(e);
-      throw FlutterZsdkException("Failed to open connection to printer: ${e.details}");
+      throw FlutterZsdkException(e.code, "Failed to open connection to printer: ${e.details}");
 
     } catch (e) {
-      throw FlutterZsdkException("Failed to open connection to printer: $e");
+      throw FlutterZsdkException(ErrorCode.unexpectedError, "Message: $e");
     }
   }
 
   @override
   Future<bool> isConnected() async {
-    bool isConnected = await methodChannel.invokeMethod('isConnected');
+    try {
+      bool isConnected = await methodChannel.invokeMethod('isConnected');
+      return isConnected;
+    } on PlatformException catch (e) {
+      throw FlutterZsdkException(e.code, "Failed to check connection , message: ${e.details}");
+    } catch (e) {
+      throw FlutterZsdkException(ErrorCode.unexpectedError, "Message: $e");
+    }
 
-    return isConnected;
   }
 
   @override
   Future<void> closeConnection() async {
     try {
       await methodChannel.invokeMethod('bluetoothCloseConnection');
+    } on PlatformException catch (e) {
+      inspect(e);
+      throw FlutterZsdkException(e.code, "Failed to close connection, message: ${e.details}");
     } catch (e) {
-      throw FlutterZsdkException("Failed to close connection to printer: $e");
+      throw FlutterZsdkException(ErrorCode.unexpectedError, "Message: $e");
     }
   }
 
   Future<void> printZplOverBluetooth(String zplData) async {
     try {
       await methodChannel.invokeMethod('printZplOverBluetooth', {'zplData': zplData});
+    } on PlatformException catch (e) {
+      inspect(e);
+      throw FlutterZsdkException(e.code, "Failed to print ZPL over Bluetooth, message: ${e.details}");
     } catch (e) {
-      throw FlutterZsdkException("Failed to print ZPL over Bluetooth: $e");
+      throw FlutterZsdkException(ErrorCode.unexpectedError, "Message: $e");
     }
   }
 }

lib/src/models/error_code.dart

+class ErrorCode {
+  static const String permissionNotGranted = "PERMISSION_NOT_GRANTED";
+  static const String turnOnBluetoothError = "TURN_ON_BLUETOOTH_ERROR";
+  static const String bluetoothIsNotSupported = "BLUETOOTH_IS_NOT_SUPPORTED";
+  static const String bluetoothDisabled = "BLUETOOTH_DISABLED";
+
+  static const String discoveryError = "DISCOVERY_ERROR";
+  static const String openConnectionError = "OPEN_CONNECTION_ERROR";
+  static const String closeAndReopenConnectionError = "CLOSE_AND_REOPEN_CONNECTION_ERROR";
+  static const String connectionHasNotBeenEstablished = "CONNECTION_HAS_NOT_BEEN_ESTABLISHED";
+  static const String checkConnectionError = "CHECK_CONNECTION_ERROR";
+  static const String closeConnectionError = "CLOSE_CONNECTION_ERROR";
+  static const String writeError = "WRITE_ERROR";
+
+  static const String unexpectedError = "UNEXPECTED_ERROR";
+}

lib/src/models/flutter_zsdk_exception.dart

 class FlutterZsdkException implements Exception {
+  String code;
   String message;
 
-  FlutterZsdkException(this.message);
+  FlutterZsdkException(this.code, this.message);
 
   @override
   String toString() {