如何执行写方法的功能，改变值在滑条?

Question

当滑动条值改变时，它尝试写一个数据包。我在用这个例子，我做了一个函数并尝试了它，但是出现了一个null错误。(discoverService、特点. .等)。我怎么解决这个问题?

我用flutter_blue

在flutter_blue示例中，write工作得很好。

我是一个初学者。我需要你的帮助。谢谢你。

https://pub.dev/packages/flutter_blue

onWriteData

var data = [0x80, 0x80, 0xF0, 0x7D, 0x05, 0x00, 0x0E, 0x01, 60, 100, 00,0x80, 0xF7];
FlutterBlue flutterBlue = FlutterBlue.instance;
BluetoothDevice device;
BluetoothService service;

onWriteData() async {
List<BluetoothService> services = await device.discoverServices();
services.forEach((service) {
});
var characteristics = service.characteristics;
for(BluetoothCharacteristic c in characteristics) {
List<int> value = await c.read();
print(value);
await c.write(data);
}
}

<<p>滑杆类/em>

class slidecontrollerr extends State<slidecontroller> {
static double volumeValue = 60;

void onVolumeChanged(double value) async { **// I want to execute the write function here**
setState(()  {
volumeValue = value;
});
onWriteData();  **//error**
}
@override 
Widget build(BuildContext context) {
return Scaffold(
.
.
.

(错误代码)[1]

E/flutter ( 5640): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: NoSuchMethodError: The method 'discoverServices' was called on null.
E/flutter ( 5640): Receiver: null
E/flutter ( 5640): Tried calling: discoverServices()
E/flutter ( 5640): #0      Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5)
E/flutter ( 5640): #1      onWriteData (package:auto_humidity/main.dart:467:48)
E/flutter ( 5640): #2      slidecontrollerr.onVolumeChanged (package:auto_humidity/main.dart:1489:5)
E/flutter ( 5640): #3      RenderRadialAxisParent.createPointerValueChangedArgs (package:syncfusion_flutter_gauges/src/radial_gauge/axis/radial_axis_parent_widget.dart:584:43)
E/flutter ( 5640): #4      RenderRadialAxisParent._setCurrentPointerValue (package:syncfusion_flutter_gauges/src/radial_gauge/axis/radial_axis_parent_widget.dart:548:5)
E/flutter ( 5640): #5      RenderRadialAxisParent._updateDragValue (package:syncfusion_flutter_gauges/src/radial_gauge/axis/radial_axis_parent_widget.dart:527:7)
E/flutter ( 5640): #6      RenderRadialAxisParent._updatePointerValue (package:syncfusion_flutter_gauges/src/radial_gauge/axis/radial_axis_parent_widget.dart:452:7)
E/flutter ( 5640): #7      RenderRadialAxisParent._handleDragUpdate (package:syncfusion_flutter_gauges/src/radial_gauge/axis/radial_axis_parent_widget.dart:339:5)
E/flutter ( 5640): #8      DragGestureRecognizer._checkUpdate.<anonymous closure> (package:flutter/src/gestures/monodrag.dart:436:55)
E/flutter ( 5640): #9      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:182:24)
E/flutter ( 5640): #10     DragGestureRecognizer._checkUpdate (package:flutter/src/gestures/monodrag.dart:436:7)
E/flutter ( 5640): #11     DragGestureRecognizer.handleEvent (package:flutter/src/gestures/monodrag.dart:289:9)
E/flutter ( 5640): #12     PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:93:12)
E/flutter ( 5640): #13     PointerRouter._dispatchEventToRoutes.<anonymous closure> (package:flutter/src/gestures/pointer_router.dart:138:9)
E/flutter ( 5640): #14     _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:397:8)
E/flutter ( 5640): #15     PointerRouter._dispatchEventToRoutes (package:flutter/src/gestures/pointer_router.dart:136:18)
E/flutter ( 5640): #16     PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:122:7)
E/flutter ( 5640): #17     GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:439:19)
E/flutter ( 5640): #18     GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:419:22)
E/flutter ( 5640): #19     RendererBinding.dispatchEvent (package:flutter/src/rendering/binding.dart:287:11)
E/flutter ( 5640): #20     GestureBinding._handlePointerEventImmediately (package:flutter/src/gestures/binding.dart:374:7)
E/flutter ( 5640): #21     GestureBinding.handlePointerEvent (package:flutter/src/gestures/binding.dart:338:5)
E/flutter ( 5640): #22     GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:296:7)
E/flutter ( 5640): #23     GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:279:7)
E/flutter ( 5640): #24     _rootRunUnary (dart:async/zone.dart:1370:13)
E/flutter ( 5640): #25     _CustomZone.runUnary (dart:async/zone.dart:1265:19)
E/flutter ( 5640): #26     _CustomZone.runUnaryGuarded (dart:async/zone.dart:1170:7)
E/flutter ( 5640): #27     _invoke1 (dart:ui/hooks.dart:182:10)
E/flutter ( 5640): #28     PlatformDispatcher._dispatchPointerDataPacket (dart:ui/platform_dispatcher.dart:282:7)
E/flutter ( 5640): #29     _dispatchPointerDataPacket (dart:ui/hooks.dart:96:31)

Answer 1

您需要连接BLE设备的特定service和characteristics

下面是我使用

的一段代码

final String serviceUUID = "0000ffe0-0000-1000-8000-00805f9b34fb";
final String characteristicWriteUUID = "0000fff1-0000-1000-8000-00805f9b34fb";
final String characteristicReadUUID = "0000fff2-0000-1000-8000-00805f9b34fb";

这些服务和特征必须默认或手动在模块中设置

discoverServices(BluetoothDevice device) async {
if (device == null) return;
List<BluetoothService> services = await device.discoverServices();
services.forEach((service) {
// do something with service
if (service.uuid.toString().toLowerCase() == serviceUUID) {
service.characteristics.forEach((characteristic) {
if (characteristic.uuid.toString().toLowerCase() == characteristicReadUUID) {
targetReadCharacteristic = characteristic;
_readData(targetReadCharacteristic);
}
if (characteristic.uuid.toString().toLowerCase() == characteristicWriteUUID) {
targetWriteCharacteristic = characteristic;
writeData(targetWriteCharacteristic, [0x49, 0x44, 0x02]);
}
});
}
});
}

Future<void> writeData(characteristic, data) async{
if (characteristic == null) return;
try {
List<int> bytes = data;
await characteristic.write(bytes, withoutResponse: true );
print("data: Send: $data");
} catch (e) {
print('Data Error ${e.message} | $data');
}
}
_readData(characteristic) async {
if (!characteristic.isNotifying) {
await characteristic.setNotifyValue(true);
}
readSubScription = characteristic.value.listen((value) {
List<int> readData = new List.from(value);
if(readData.isNotEmpty && readData != []){
print('BLE read data: $readData');
}
});
}