Improve USB connection handling by preventing connection attempts when already connected

android/app/src/main/kotlin/com/meshcore/meshcore_open/MainActivity.kt

@@ -238,30 +238,45 @@ class MainActivity : FlutterActivity() {
         baudRate: Int,
         result: MethodChannel.Result,
     ) {
+        usbIoExecutor.execute {
             try {
                 closeUsbConnection()
 
                 val driver = UsbSerialProber.getDefaultProber().probeDevice(device)
                 if (driver == null) {
-                result.error("usb_driver_missing", "No USB serial driver for ${device.deviceName}", null)
-                return
+                    mainHandler.post {
+                        result.error(
+                            "usb_driver_missing",
+                            "No USB serial driver for ${device.deviceName}",
+                            null,
+                        )
+                    }
+                    return@execute
                 }
 
                 val connection = usbManager.openDevice(device)
                 if (connection == null) {
+                    mainHandler.post {
                         result.error(
                             "usb_open_failed",
                             "UsbManager could not open ${device.deviceName}",
                             null,
                         )
-                return
+                    }
+                    return@execute
                 }
 
                 val port = firstPort(driver)
                 if (port == null) {
                     connection.close()
-                result.error("usb_port_missing", "No USB serial port exposed by ${device.deviceName}", null)
-                return
+                    mainHandler.post {
+                        result.error(
+                            "usb_port_missing",
+                            "No USB serial port exposed by ${device.deviceName}",
+                            null,
+                        )
+                    }
+                    return@execute
                 }
 
                 port.open(connection)
@@ -303,12 +318,17 @@ class MainActivity : FlutterActivity() {
                         manager.start()
                     }
 
+                mainHandler.post {
                     result.success(null)
+                }
             } catch (error: Exception) {
                 closeUsbConnection()
+                mainHandler.post {
                     result.error("usb_connect_failed", error.message, null)
                 }
             }
+        }
+    }
 
     private fun firstPort(driver: UsbSerialDriver): UsbSerialPort? {
         return driver.ports.firstOrNull()

lib/screens/usb_screen.dart

@@ -425,6 +425,13 @@ class _UsbScreenState extends State<UsbScreen> {
     if (selectedPort == null || selectedPort.isEmpty) {
       return;
     }
+    if (_connector.state != MeshCoreConnectionState.disconnected) {
+      setState(() {
+        _isConnecting = false;
+        _errorText = null;
+      });
+      return;
+    }
     final rawPortName = normalizeUsbPortName(selectedPort);
 
     setState(() {