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I try to communicate with an µ-controller through an android device via BLE. I am able to write my custom characteristic (toggle an LED on my Dev-Kit) but can't read the value of the LED status ('0x00' for off, '0x01' for on).

I want to read it when i click on the ExpandableListView when i click on an item. For the moment i implemented it within the onChildClickListener. If a characteristic-permission "PROPERTY_WRITE" > 0 then it should write the value. 

private final ExpandableListView.OnChildClickListener servicesListClickListner =
            new ExpandableListView.OnChildClickListener() {
                @Override
                public boolean onChildClick(ExpandableListView parent, View v, int groupPosition,
                                            int childPosition, long id) {
                    if (mGattCharacteristics != null) {
                        final BluetoothGattCharacteristic characteristic =
                                mGattCharacteristics.get(groupPosition).get(childPosition);
                        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);
                        }

                        if ((charaProp | BluetoothGattCharacteristic.PROPERTY_WRITE) > 0) {         

                            mBluetoothLeService.readCustomCharacteristic();
                            mBluetoothLeService.writeCustomCharacteristic(0x01);


                        }
                        return true;
                    }
                    return false;
                }

But it always fails to read the characteristic. The LED value is written and the LED switches to 'ON' but it doesn't read the value of the LED. I want to read the value for switching the LED on/off with clicking on the characteristic in my list.

I can't figure out what i'm doing wrong. It should be reading the characteristic, write it in a textfield. On my BLE-Device i have enabled reading. I can read the value with my ubuntu-terminal using gatttool -> char-read-hnd [hnd] [val].

This is my implementation of the readCustomCharacteristic() in mBluetoothLeService 

public void readCustomCharacteristic() {
        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("edfec62e-9910-0bac-5241-d8bda6932a2f"));
        if(mCustomService == null){
            Log.w(TAG, "Custom BLE Service not found");
            return;
        }
        /*get the read characteristic from the service*/
        BluetoothGattCharacteristic mReadCharacteristic = mCustomService.getCharacteristic(UUID.fromString("18192021-2223-2425-2627-282930313233"));
        mBluetoothGatt.readCharacteristic(mReadCharacteristic);

        if(mBluetoothGatt.readCharacteristic(mReadCharacteristic) == false){
            Log.w(TAG, "Failed to read characteristic");
        }
        return;
    }
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1 回答 1

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看起来您可能缺少的是将描述符设置为通知/指示。我们必须手动执行此操作很痛苦（iOS 不需要），但我想这些是我们提供的工具。这是一个可能有帮助的小片段：

BluetoothGattDescriptor descriptor = characteristic.getDescriptor(DESCRIPTOR_CONFIG_UUID);
bleGatt.setCharacteristicNotification(characteristic, true);
descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
bleGatt.writeDescriptor(descriptor);

根据您的外围设备，您可能必须将描述符值设置为 ENABLE_INDICATION_VALUE。如果你不知道描述符 UUID，你可以这样做

characteristic.getDescriptors()

获取可用描述符的列表。

编写描述符后，您应该在 gatt 回调中调用 onDescriptorWrite。如果一切正常，并且未来的特征更改应该在您的 gatt 回调中调用 onCharacteristicChanged 方法。

希望这可以帮助！

于 2016-08-30T15:30:52.170 回答