uni-app H5+API【蓝牙】安卓机写入数据后监听不到特征值的变化

uni-app H5+API【蓝牙】安卓机写入数据后监听不到特征值的变化

产品分类：HTML5+

手机系统：Android  
手机系统版本号：Android 10  
手机厂商：小米  
手机机型：mi8  
打包方式：云端  

### 示例代码：

```javascript
<script type="text/javascript" charset="utf-8">  
    function ab2hex(buffer) {  
      var hexArr = Array.prototype.map.call(  
        new Uint8Array(buffer),  
        function (bit) {  
          return ('00' + bit.toString(16)).slice(-2)  
        }  
      )  
      return hexArr.join('');  
    }  

    function str2ab(str){  
      var buffer = new ArrayBuffer(str.length)  
      var dataView = new DataView(buffer)  
      for (let i = 0; i < str.length; i++) {  
        dataView.setInt8(i, str.charCodeAt(i))  
      }  
      return buffer  
    }  

    mui.init();  
    mui.plusReady(function() {  
        characteristicValueChange();  

        var deviceId = '',serviceId = '', writeCharacteristic='0000FFF5-0000-1000-8000-00805F9B34FB';  

        // 点击初始化蓝牙模块  
        const initDom = document.getElementById('init')  
        initDom.onclick = function() {  
            plus.bluetooth.openBluetoothAdapter({  
                success(s) {  
                    console.log('初始化蓝牙模块成功')  
                },  
                fail(f) {  
                    console.log('初始化蓝牙模块失败' + JSON.stringify(f))  
                }  
            })  
        }  

        // 点击扫描设备  
        const searchDom = document.getElementById('search')  
        searchDom.onclick = function() {  
            plus.bluetooth.startBluetoothDevicesDiscovery({  
                services: ['FFF0'],  
                success(s) {  
                    console.log('开始扫描')  
                    onBluetoothFound()  
                },  
                fail(f) {  
                    console.log('开启扫描失败'+JSON.stringify(f))  
                }  
            })  
        }  

        // 点击连接设备  
        const ulDom = document.getElementById('devices-ul')  
        ulDom.addEventListener('click', ev => {  
            if(ev.target && ev.target.nodeName.toLowerCase() == 'li'){  
                deviceId = ev.target.getAttribute('id')  
                connectionBluetooth(deviceId)  
            }  
        })  

        // 点击写入数据  
        const sendDom = document.getElementById('sendValue')  
        sendDom.onclick = function (){  
            const value = document.getElementById('value').value  
            if(value){  
                const wValue = str2ab(value)  
                plus.bluetooth.writeBLECharacteristicValue({  
                    deviceId: deviceId,  
                    serviceId: serviceId,  
                    characteristicId: writeCharacteristic,  
                    value: wValue,  
                    success(s) {  
                        console.log('写入成功' + JSON.stringify(s))  
                    },  
                    fail(f) {  
                        console.log('写入失败' + JSON.stringify(f))  
                    }  
                })  
            }  
        }  

        // 监听/主动调用发现设备  
        function onBluetoothFound(){  
            plus.bluetooth.onBluetoothDeviceFound(res => {  
                res.devices.forEach(device => {  
                    if(!device.name || !device.localName){  
                        return  
                    }  
                    if(document.getElementById(device.deviceId) == null){  
                        console.log('发现设备' + JSON.stringify(device))  
                        var liDom = document.createElement('li')  
                        liDom.setAttribute('id', device.deviceId)  
                        liDom.innerHTML = device.name  
                        document.getElementById('devices-ul').appendChild(liDom)  
                    }  
                })  
            })  
        }  

        // 连接蓝牙  
        function connectionBluetooth(deviceId){  
            plus.bluetooth.createBLEConnection({  
                deviceId: deviceId,  
                success(s) {  
                    console.log('蓝牙设备连接成功')  
                    // 获取服务  
                    setTimeout(getService, 1500);  
                }  
            })  
            // 关闭搜索  
            stopSearch()  
        }  

        // 获取服务  
        function getService(){  
            console.log(deviceId)  
            plus.bluetooth.getBLEDeviceServices({  
                deviceId: deviceId,  
                success(s) {  
                    console.log('获取服务成功' + JSON.stringify(s))  
                    serviceId = '0000FFF0-0000-1000-8000-00805F9B34FB'  
                    getCharacteristics(deviceId, serviceId)  
                },  
                fail(f) {  
                    console.log('获取服务失败' + JSON.stringify(f))  
                }  
            })  
        }  

        // 获取特征值  
        function getCharacteristics(deviceId, serviceId){  
            plus.bluetooth.getBLEDeviceCharacteristics({  
                deviceId: deviceId,  
                serviceId: serviceId,  
                success(s){  
                    console.log('获取特征值成功' + JSON.stringify(s))  
                    // 订阅 notify 特征值  
                    s.characteristics.forEach(characteristic => {  
                        if(characteristic.properties.notify || characteristic.properties.indicate){  
                            if(characteristic.uuid != writeCharacteristic){  
                                plus.bluetooth.notifyBLECharacteristicValueChange({  
                                    state: true,  
                                    deviceId: deviceId,  
                                    serviceId: serviceId,  
                                    characteristicId: characteristic.uuid,  
                                    success(s) {  
                                        console.log('特征值订阅成功：' + characteristic.uuid)  
                                    },  
                                    fail(f) {  
                                        console.log('特征值订阅失败' + JSON.stringify(f))  
                                    }  
                                })  
                            }  
                        }  
                    })  
                },  
                fail(f) {  
                    console.log('获取特征值失败' + JSON.stringify(f))  
                }  
            })  
        }  

        // 特征值变化  
        function characteristicValueChange(){  
            console.log('监听特征值了哦')  
            plus.bluetooth.onBLECharacteristicValueChange(res => {  
                alert(JSON.stringify(res.value))  
                console.log('监听到特征值数据 16进制：'+ ab2hex(res.value))  
                const resValue = new Uint8Array(res.value, 0)  
                console.log('监听到特征值数据 二进制：'+ resValue)  
                const tmp = String.fromCharCode.apply(String, resValue)  
                console.log('监听到特征值数据 字符串：' + tmp)  
            })  
        }         

        // 停止搜索  
        function stopSearch(){  
            plus.bluetooth.stopBluetoothDevicesDiscovery({  
                success(s) {  
                    console.log('停止搜索蓝牙设备成功')  
                }  
            })  
        }         
    })  
</script>

操作步骤：

1. onBLECharacteristicValueChange
2. openBluetoothAdapter
3. startBluetoothDevicesDiscovery
4. onBluetoothDeviceFound
5. createBLEConnection -> stopBluetoothDevicesDiscovery
6. getBLEDeviceServices（延迟1.5s）
7. getBLEDeviceCharacteristics
8. notifyBLECharacteristicValueChange
9. writeBLECharacteristicValue

预期结果：

写入后能监听到notify下的特征值返回信息

实际结果：

写入成功 ok, 没有监听到

bug描述：

低功耗蓝牙模块，无论是使用官方的demo还是自己写的，都是在先注册监听特征值变化后，再获取服务的特征值成功回调的方法里订阅了notify，主动的写入数据，无法监听