使用Flutter+Android Studio开发BLE可写入但无法读取的问题

问题 #

使用Flutter + Android Studio，通过flutter_blue_plus库开发BLE蓝牙读写应用时，可正常写入数据，但读取时报错，调换读写顺序问题依旧。

报错信息：

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: PlatformException(readCharacteristic, The READ property is not supported by this BLE characteristic, null, null)

相关读写代码：

bleBuilder!.writeData();
bleBuilder!.readData();

void writeData() {
  String serviceUUID = accDataCharacteristic!.serviceUuid.toString();
  String sUUID = accDataCharacteristic!.uuid.toString();
  String characterUUID = accDataCharacteristic!.characteristicUuid.toString();
  print('writeData  serviceUUID '+ serviceUUID + ' sUUID '+ sUUID + ' characterUUID '+ characterUUID);
  accDataCharacteristic?.write([51, 52, 99, 100]);
}

void readData(){
  String serviceUUID = accDataCharacteristic!.serviceUuid.toString();
  String sUUID = accDataCharacteristic!.uuid.toString();
  String characterUUID = accDataCharacteristic!.characteristicUuid.toString();
  print('readData  serviceUUID '+ serviceUUID + ' sUUID '+ sUUID + ' characterUUID '+ characterUUID);
}

日志信息：

I/flutter (11323): floatingActionButton onPressed 
I/flutter (11323): writeData  serviceUUID 6e400001-b5a3-f393-e0a9-e50e24dcca9e     sUUID 6e400002-b5a3-f393-e0a9-e50e24dcca9e characterUUID 6e400002-b5a3-f393-e0a9-e50e24dcca9e
I/flutter (11323): readData  serviceUUID 6e400001-b5a3-f393-e0a9-e50e24dcca9e sUUID 6e400002-b5a3-f393-e0a9-e50e24dcca9e characterUUID 6e400002-b5a3-f393-e0a9-e50e24dcca9e
I/flutter (11323): readData Instance of 'Future<List<int>>'
I/flutter (11323): Instance of 'Future<List<int>>'
I/flutter (11323): [FBP] <writeCharacteristic> args: {remote_id: D4:EC:FA:03:64:55, service_uuid: 6e400001-b5a3-f393-e0a9-e50e24dcca9e, secondary_service_uuid: null, characteristic_uuid: 6e400002-b5a3-f393-e0a9-e50e24dcca9e, write_type: 0, allow_long_write: 0, value: 33346364}
D/[FBP-Android](11323): [FBP] onMethodCall: writeCharacteristic
D/[FBP-Android](11323): [FBP] onCharacteristicWrite:
D/[FBP-Android](11323): [FBP]   chr: 6e400002-b5a3-f393-e0a9-e50e24dcca9e
D/[FBP-Android](11323): [FBP]   status: GATT_SUCCESS (0)
I/flutter (11323): [FBP] <writeCharacteristic> result: true
I/flutter (11323): [FBP] [[ OnCharacteristicWritten ]] result: {error_string:     GATT_SUCCESS, service_uuid: 6e400001-b5a3-f393-e0a9-e50e24dcca9e, success: 1, remote_id: D4:EC:FA:03:64:55, error_code: 0, characteristic_uuid: 6e400002-b5a3-f393-e0a9-e50e24dcca9e, value: 33346364}
I/flutter (11323): [FBP] <readCharacteristic> args: {remote_id: D4:EC:FA:03:64:55, service_uuid: 6e400001-b5a3-f393-e0a9-e50e24dcca9e, secondary_service_uuid: null, characteristic_uuid: 6e400002-b5a3-f393-e0a9-e50e24dcca9e}
D/[FBP-Android](11323): [FBP] onMethodCall: readCharacteristic
I/gralloc4(11323): @set_metadata: update dataspace from GM (0x00000000 -> 0x08010000)
E/flutter (11323): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled     Exception: PlatformException(readCharacteristic, The READ property is not supported by this BLE characteristic, null, null)
E/flutter (11323): #0      StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:648:7)
E/flutter (11323): #1      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:334:18)
E/flutter (11323): <asynchronous suspension>
E/flutter (11323): #2      FlutterBluePlus._invokeMethod (package:flutter_blue_plus/src/flutter_blue_plus.dart:603:13)
E/flutter (11323): <asynchronous suspension>
E/flutter (11323): #3      BluetoothCharacteristic.read (package:flutter_blue_plus/src/bluetooth_characteristic.dart:130:7)
E/flutter (11323): <asynchronous suspension>

报错含义与解决方案 #

报错含义 #

该报错明确说明：你当前操作的BLE特征值（Characteristic）不支持READ属性，即这个特征值仅允许写入操作，不允许主动读取。从日志和代码可见，你读写用的是同一个特征值UUID 6e400002-b5a3-f393-e0a9-e50e24dcca9e，而BLE设备的特征值通常分工明确：部分负责写入指令，部分负责返回数据（通过主动读或通知推送）。

解决方案 #

1. 排查目标服务下的所有特征值属性
   先扫描目标服务的全部特征值，检查每个特征值的properties字段，找到支持read或notify属性的特征值：

   // 遍历服务下的所有特征值
   for (var chr in targetService.characteristics) {
     print("特征值UUID: ${chr.uuid}, 支持属性: ${chr.properties}");
     if (chr.properties.read) {
       print("该特征值支持主动读取");
     }
     if (chr.properties.notify) {
       print("该特征值支持通知推送");
     }
   }
   

2. 更换到支持读/通知的特征值获取数据
   BLE设备返回数据大多用**通知（Notify）**方式，而非主动读取。找到支持notify属性的特征值，订阅通知接收数据：

   // 筛选支持通知的特征值
   var notifyCharacteristic = targetService.characteristics.firstWhere(
     (chr) => chr.properties.notify,
     orElse: () => throw Exception("未找到支持通知的特征值")
   );
   // 开启通知订阅
   await notifyCharacteristic.setNotifyValue(true);
   // 监听通知数据
   notifyCharacteristic.value.listen((data) {
     print("收到设备推送数据: $data");
   });
   

   如果确实需要主动读取，就更换到带有read属性的特征值执行读取操作。

3. 修正异步操作逻辑
   BLE读写都是异步操作，需用await确保操作顺序和结果获取：

   • 调用读写方法时：

     await bleBuilder!.writeData();
     await bleBuilder!.readData();
     

   • 完善readData方法的异步处理：

     Future<void> readData() async {
       // 打印UUID代码...
       try {
         List<int> data = await accDataCharacteristic!.read();
         print("读取到数据: $data");
       } catch (e) {
         print("读取失败: $e");
       }
     }
     

内容的提问来源于stack exchange，提问作者t h