无法从 BLE 设备读取特征值

Posted 2023-03-05

【中文标题】无法从 BLE 设备读取特征值

【英文标题】：Not able to read a characteristic value from BLE device

【发布时间】：2016-08-08 12:18:31

【问题描述】：

我需要向 android BLE 设备写入和读取特征值。我会写但不会读。这是我的写作方式：

public void writeCustomCharacteristic(int value) 
    if (mBluetoothAdapter == null || mBluetoothGatt == null) 
        Log.w(TAG, "BluetoothAdapter not initialized");
        return;
    
    /*check if the service is available on the device*/
    BluetoothGattService mCustomService = mBluetoothGatt.getService(UUID.fromString("<MY SERVICE UUID>"));
    if(mCustomService == null)
        Log.w(TAG, "Custom BLE Service not found");
        return;
    
    /*get the read characteristic from the service*/
    BluetoothGattCharacteristic mWriteCharacteristic = mCustomService.getCharacteristic(UUID.fromString("<MY CHARACTERSTIC UUID>"));
   mWriteCharacteristic.setWriteType(BluetoothGattCharacteristic.WRITE_TYPE_NO_RESPONSE);
       mWriteCharacteristic.setValue(value,BluetoothGattCharacteristic.FORMAT_UINT8,0);
    if(!mBluetoothGatt.writeCharacteristic(mWriteCharacteristic))
        Log.w(TAG, "Failed to write characteristic");
    else
        Log.w(TAG, "Success to write characteristic");
    

如果我使用这个操作是成功的

 mWriteCharacteristic.setWriteType(BluetoothGattCharacteristic.WRITE_TYPE_NO_RESPONSE);

如果我使用任何其他写入类型而不是WRITE_TYPE_NO_RESPONSE，那么它不会触发onCharacteristicWrite() 回调方法。

这是我阅读特征的方式：

 private boolean readCharacteristics(int groupPosition,int childPosition)
    try
        if (mGattCharacteristics != null) 
            final BluetoothGattCharacteristic characteristic = mGattCharacteristics.get(2).get(2);
            final int charaProp = characteristic.getProperties();
            if ((charaProp | BluetoothGattCharacteristic.PROPERTY_READ) > 0) 
                // If there is an active notification on a characteristic, clear
                // it first so it doesn't update the data field on the user interface.
                if (mNotifyCharacteristic != null) 
                    mBluetoothLeService.setCharacteristicNotification(mNotifyCharacteristic, false);
                    mNotifyCharacteristic = null;
                
                mBluetoothLeService.readCharacteristic(characteristic);
            
            if ((charaProp | BluetoothGattCharacteristic.PROPERTY_NOTIFY) > 0) 
                mNotifyCharacteristic = characteristic;
                mBluetoothLeService.setCharacteristicNotification(characteristic, true);
            
            waitSometime(100);
            if ((charaProp | BluetoothGattCharacteristic.PROPERTY_INDICATE) > 0) 
                mNotifyCharacteristic = characteristic;
                mBluetoothLeService.setCharacteristicIndication(characteristic, true);
            
            waitSometime(100);
            if ((charaProp | BluetoothGattCharacteristic.PROPERTY_WRITE) > 0) 

                byte[] value = characteristic.getValue(); //this is being NULL always

                if (mNotifyCharacteristic != null) 
                    mBluetoothLeService.setCharacteristicNotification(mNotifyCharacteristic, true);
                    mNotifyCharacteristic = null;
                
                mBluetoothLeService.writeCharacteristic(characteristic, value);
                if(value!=null&&value.length>0) 
                    Toast.makeText(DeviceControlActivity.this,"success reading data",Toast.LENGTH_LONG).show();
                else
                  Toast.makeText(DeviceControlActivity.this,"error reading data",Toast.LENGTH_LONG).show();
                
            
       /* if ((charaProp | BluetoothGattCharacteristic.PROPERTY_INDICATE) > 0) 
            mNotifyCharacteristic = characteristic;
            //characteristic.setWriteType();
            mBluetoothLeService.setCharacteristicIndication(
                    characteristic, true);
            byte[] value=characteristic.getValue();
        */
            return true;
        
    catch (Exception e)
        e.printStackTrace();
    
    return false;

characteristic.getValue() 始终返回 null。我哪里错了？

【问题讨论】：

您错误地使用了 bitor 而不是 bitand。另外，不要睡觉，然后期望该值已被读取。而是等待通知读取何时完成的回调。

【参考方案1】：

这是我的看法：

您需要弄清楚您将获得什么样的特征数据？其中一些需要先设置指示或通知！喜欢：

一个。获取特征描述符

   BluetoothGattDescriptor descriptor = gattCharacteristic.getDescriptors().get(0); 
     //Usually is Client_Characteristic_Configuration

b.根据特性，设置描述符的property()为true。

if ((gattCharacteristic.PROPERTY_NOTIFY)> 0 )
    if (descriptor != null) 
       descriptor.setValue((BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE));
       
   
else if((gattCharacteristic.PROPERTY_INDICATE) >0 )
    if(descriptor != null)
       descriptor.setValue(BluetoothGattDescriptor.ENABLE_INDICATION_VALUE);
       
   

c。将值发送到远程 BLE 设备。

gatt.writeDescriptor(descriptor);

之后，你可以在回调函数中获取数据：

onCharacteristicChanged

至少以上对我有用！ 希望能帮到人~

【讨论】：

你救了我的命