【发布时间】：2021-06-02 08:32:36
【问题描述】：
首先，当我几个月前下载 Flutter 蓝牙串行插件时，它运行良好。 但是现在，当我运行该应用程序时，它会引发以下异常和错误。
1.当我选择设备并尝试连接它们时发生此错误
- 当我点击刷新按钮时出现此错误
这是蓝牙插件的代码。
import 'dart:async';
import 'dart:convert';
// For using PlatformException
import 'package:flutter/services.dart';
import 'package:flutter/material.dart';
import 'package:flutter_bluetooth_serial/flutter_bluetooth_serial.dart';
class BluetoothApp extends StatefulWidget {
@override
_BluetoothAppState createState() => _BluetoothAppState();
}
class _BluetoothAppState extends State<BluetoothApp> {
// Initializing the Bluetooth connection state to be unknown
BluetoothState _bluetoothState = BluetoothState.UNKNOWN;
// Initializing a global key, as it would help us in showing a SnackBar later
final GlobalKey<ScaffoldMessengerState> _scaffoldKey = new GlobalKey<ScaffoldMessengerState>();
// Get the instance of the Bluetooth
FlutterBluetoothSerial _bluetooth = FlutterBluetoothSerial.instance;
// Track the Bluetooth connection with the remote device
BluetoothConnection connection;
int _deviceState;
bool isDisconnecting = false;
Map<String, Color> colors = {
'onBorderColor': Colors.green,
'offBorderColor': Colors.red,
'neutralBorderColor': Colors.transparent,
'onTextColor': Colors.green[700],
'offTextColor': Colors.red[700],
'neutralTextColor': Colors.blue,
};
// To track whether the device is still connected to Bluetooth
bool get isConnected => connection != null && connection.isConnected;
// Define some variables, which will be required later
List<BluetoothDevice> _devicesList = [];
BluetoothDevice _device;
bool _connected = false;
bool _isButtonUnavailable = false;
@override
void initState() {
super.initState();
// Get current state
FlutterBluetoothSerial.instance.state.then((state) {
setState(() {
_bluetoothState = state;
});
});
_deviceState = 0; // neutral
// If the bluetooth of the device is not enabled,
// then request permission to turn on bluetooth
// as the app starts up
enableBluetooth();
// Listen for further state changes
FlutterBluetoothSerial.instance
.onStateChanged()
.listen((BluetoothState state) {
setState(() {
_bluetoothState = state;
if (_bluetoothState == BluetoothState.STATE_OFF) {
_isButtonUnavailable = true;
}
getPairedDevices();
});
});}
@override
void dispose() {
// Avoid memory leak and disconnect
if (isConnected) {
isDisconnecting = true;
connection.dispose();
connection = null;
}
super.dispose();}
// Request Bluetooth permission from the user
Future<void> enableBluetooth() async {
// Retrieving the current Bluetooth state
_bluetoothState = await FlutterBluetoothSerial.instance.state;
// If the bluetooth is off, then turn it on first
// and then retrieve the devices that are paired.
if (_bluetoothState == BluetoothState.STATE_OFF) {
await FlutterBluetoothSerial.instance.requestEnable();
await getPairedDevices();
return true;
} else {
await getPairedDevices();
}
return false;}
// For retrieving and storing the paired devices
// in a list.
Future<void> getPairedDevices() async {
List<BluetoothDevice> devices = [];
// To get the list of paired devices
try {
devices = await _bluetooth.getBondedDevices();
} on PlatformException {
print("Error");}
// It is an error to call [setState] unless [mounted] is true.
if (!mounted) {
return;}
// Store the [devices] list in the [_devicesList] for accessing
// the list outside this class
setState(() {
_devicesList = devices;
});}
// Now, its time to build the UI
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
key: _scaffoldKey,
appBar: AppBar(
title: Text("Pair Bluetooth Device"),
backgroundColor: Colors.green[900],
actions: <Widget>[
FlatButton.icon(
icon: Icon(
Icons.refresh,
color: Colors.white,
),
label: Text(
"Refresh",
style: TextStyle(
color: Colors.white,
),
),
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(30),
),
splashColor: Colors.deepPurple,
onPressed: () async {
// So, that when new devices are paired
// while the app is running, user can refresh
// the paired devices list.
await getPairedDevices().then((_) {
show('Device list refreshed');
});
},
),
],
),
body: Container(
child: Column(
mainAxisSize: MainAxisSize.max,
children: <Widget>[
Visibility(
visible: _isButtonUnavailable &&
_bluetoothState == BluetoothState.STATE_ON,
child: LinearProgressIndicator(
backgroundColor: Colors.yellow,
valueColor: AlwaysStoppedAnimation<Color>(Colors.red),
),
),
Padding(
padding: const EdgeInsets.all(10),
child: Row(
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
Expanded(
child: Text(
'Enable Bluetooth',
style: TextStyle(
color: Colors.black,
fontSize: 16,
),
),
),
Switch(
value: _bluetoothState.isEnabled,
onChanged: (bool value) {
future() async {
if (value) {
await FlutterBluetoothSerial.instance
.requestEnable();
} else {
await FlutterBluetoothSerial.instance
.requestDisable();
}
await getPairedDevices();
_isButtonUnavailable = false;
if (_connected) {
_disconnect();
}
}
future().then((_) {
setState(() {});
});
},
)
],
),
),
Stack(
children: <Widget>[
Column(
children: <Widget>[
Padding(
padding: const EdgeInsets.only(top: 10),
child: Text(
"PAIRED DEVICES",
style: TextStyle(fontSize: 24, color: Colors.blue,
fontFamily: 'RussoOne'
),
textAlign: TextAlign.center,
),
),
Padding(
padding: const EdgeInsets.all(8.0),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Text(
'Device:',
style: TextStyle(
fontWeight: FontWeight.bold,
),
),
DropdownButton(
items: _getDeviceItems(),
onChanged: (value) =>
setState(() => _device = value),
value: _devicesList.isNotEmpty ? _device : null,
),
ElevatedButton(
onPressed: _isButtonUnavailable
? null
: _connected ? _disconnect : _connect,
child:
Text(_connected ? 'Disconnect' : 'Connect'),
),
],
),
),
Padding(
padding: const EdgeInsets.all(16.0),
child: Card(
shape: RoundedRectangleBorder(
side: new BorderSide(
color: _deviceState == 0
? colors['neutralBorderColor']
: _deviceState == 1
? colors['onBorderColor']
: colors['offBorderColor'],
width: 3,
),
borderRadius: BorderRadius.circular(4.0),
),
elevation: _deviceState == 0 ? 4 : 0,
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Row(
children: <Widget>[
Expanded(
child: Text(
"DEVICE 1",
style: TextStyle(
fontSize: 20,
color: _deviceState == 0
? colors['neutralTextColor']
: _deviceState == 1
? colors['onTextColor']
: colors['offTextColor'],
),
),
),
TextButton(
onPressed: _connected
? _sendOnMessageToBluetooth
: null,
child: Text("ON"),
),
TextButton(
onPressed: _connected
? _sendOffMessageToBluetooth
: null,
child: Text("OFF"),
),
],
),
),
),
),
],
),
Container(
color: Colors.blue,
),
],
),
Expanded(
child: Padding(
padding: const EdgeInsets.all(20),
child: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
"NOTE: If you cannot find the device in the list, please pair the device by going to the bluetooth settings",
style: TextStyle(
fontSize: 15,
fontWeight: FontWeight.bold,
color: Colors.red,
),
),
SizedBox(height: 15),
TextButton.icon(
//color: Colors.blueAccent,
style: TextButton.styleFrom(
elevation: 2,
backgroundColor: Colors.blueAccent,
),
icon: Icon(Icons.bluetooth,
color: Colors.white,
),
label: Text("Settings",
style: TextStyle(
fontFamily: 'RussoOne',
color: Colors.white
),
),
onPressed: () {
FlutterBluetoothSerial.instance.openSettings();
},
),
SizedBox(height: 15),
TextButton(
//color: Colors.black,
style: TextButton.styleFrom(
backgroundColor: Colors.black,
),
child: Text("Home",
style: TextStyle(
fontFamily: 'RussoOne',
color: Colors.white
),
),
onPressed: () {
Navigator.pop(context);
},
),
],
),
),
),
)
],
),
),
),
);}
// Create the List of devices to be shown in Dropdown Menu
List<DropdownMenuItem<BluetoothDevice>> _getDeviceItems() {
List<DropdownMenuItem<BluetoothDevice>> items = [];
if (_devicesList.isEmpty) {
items.add(DropdownMenuItem(
child: Text('NONE'),
));
} else {
_devicesList.forEach((device) {
items.add(DropdownMenuItem(
child: Text(device.name),
value: device,
));
});
}
return items;}
// Method to connect to bluetooth
void _connect() async {
setState(() {
_isButtonUnavailable = true;
});
if (_device == null) {
show('No device selected');
} else {
if (!isConnected) {
await BluetoothConnection.toAddress(_device.address)
.then((_connection) {
print('Connected to the device');
connection = _connection;
setState(() {
_connected = true;
});
connection.input.listen(null).onDone(() {
if (isDisconnecting) {
print('Disconnecting locally!');
} else {
print('Disconnected remotely!');
}
if (this.mounted) {
setState(() {});
}
});
}).catchError((error) {
print('Cannot connect, exception occurred');
print(error);
});
show('Device connected');
setState(() => _isButtonUnavailable = false);
}} }
// void _onDataReceived(Uint8List data) {
// // Allocate buffer for parsed data
// int backspacesCounter = 0;
// data.forEach((byte) {
// if (byte == 8 || byte == 127) {
// backspacesCounter++;
// }
// });
// Uint8List buffer = Uint8List(data.length - backspacesCounter);
// int bufferIndex = buffer.length;
// // Apply backspace control character
// backspacesCounter = 0;
// for (int i = data.length - 1; i >= 0; i--) {
// if (data[i] == 8 || data[i] == 127) {
// backspacesCounter++;
// } else {
// if (backspacesCounter > 0) {
// backspacesCounter--;
// } else {
// buffer[--bufferIndex] = data[i];
// }
// }
// }
// }
// Method to disconnect bluetooth
void _disconnect() async {
setState(() {
_isButtonUnavailable = true;
_deviceState = 0;
});
await connection.close();
show('Device disconnected');
if (!connection.isConnected) {
setState(() {
_connected = false;
_isButtonUnavailable = false;
});
}}
// Method to send message,
// for turning the Bluetooth device on
void _sendOnMessageToBluetooth() async {
connection.output.add(utf8.encode("1" + "\r\n"));
await connection.output.allSent;
show('Device Turned On');
setState(() {
_deviceState = 1; // device on
});}
// Method to send message,
// for turning the Bluetooth device off
void _sendOffMessageToBluetooth() async {
connection.output.add(utf8.encode("0" + "\r\n"));
await connection.output.allSent;
show('Device Turned Off');
setState(() {
_deviceState = -1; // device off
});}
// Method to show a Snackbar,
// taking message as the text
Future show(
String message, {
Duration duration: const Duration(seconds: 3),
}) async {
await new Future.delayed(new Duration(milliseconds: 100));
_scaffoldKey.currentState.showSnackBar(
SnackBar(
content:Text(
message,
),
duration: duration,
),
); }}
我在互联网上搜索了很多关于这些错误的信息，但没有找到令人满意的解决方案。 请解决这个问题。 我将不胜感激。 提前致谢。
【问题讨论】：
标签： flutter dart error-handling bluetooth sdk