关于android：无法从BLE设备读取特征值

Not able to read a characteristic value from BLE device

我需要向 Android BLE 设备写入和读取特征值。我能写但不能读。这是我的写作方式：

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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

1	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：

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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？