i'm developping an android app that communicate with a BLE device(in kotlin).
i'm sending a command to the ble device, the device usually give the following response:
-OK(confirming the command was received and valid)
-one or multiple line of data
-Done
in onCharacteristicWrite i tryed to show this.value to read the response but look like it's not the way to do it. i googled a lot without lot of success.
so my question is how could i get the data from the response.the device send?
i try to call a readCharateristic without success either.
thank you for your help
GATT does not have any protocol feature of a request - response transaction where both messages embed data.
For Write Request - Write Response, only the request can contain data. The response can only be empty or an error code.
For Read Request - Read Response, the request contain only what characteristic is to be read and the response contains some data or an error code.
To implement a request - response mechanism using GATT, one usually follows one of the following strategies:
Use Write Request or Write Without Response for the request message and Notification for the response message.
Use Write Request or Write Without Response for the request message. When the GATT server produces a response message, it is put in a characteristic that the client will then read using a Read Request.
The first method has lowest overhead and best throughput.
What you should do is to investigate what method your peripheral actually uses. If it sends its responses in notifications, you must enable these and implement the onCharacteristicChanged callback.
I am invoking the writeCharacteristic both using the WRITE_TYPE_NO_RESPONSE and without it.Am I supposed to get the response out of both or one or none?
Is there any callback to catch this response?
Does onReliableWriteCompleted callBack ensures the successful delivery of the Message at the BLE device side(from the Phone) or does it implies that the message has been sent to the device(From the Phone) successfully and has been released in air.
If you use the WRITE_TYPE_NO_RESPONSE, you will get the onCharacteristicWrite callback as soon as the stack is ready and has space to accept a new request. This does not mean the other side has received it.
If you don't use WRITE_TYPE_NO_RESPONSE, you will get the onCharacteristicWrite callback as soon as the remote device has sent back a Write Response.
The onReliableWriteCompleted will be called when the remote side has acknowledged everything.
I create a monitoring application who :
if there is a network connection available : she sends periodically
measurement data to the server using json
if there is no network available, she stores the data in the sd card and sends it when the network connection is back.
Actually I use a circular buffer in memory that I empty when data are sent
Is there already something usefull in the framework or I have to write that completly ?
Thanks
I would check tape library from square. I've never tried it but looks what you are looking for.
I understand that on a wifi network there are sudden disconnections which prevent me from sending messages to my server.
But sometimes there's still one last chance before the disconnection, for example if the signal is low or the user is trying to turn off the wifi. On those occasions I would like to send a logout message to my server.
How do I detect disconnections like those?
I tried to retrieve changes of connectivity by registering a broadcast listener:
registerReceiver(this,new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION));
...
public void onReceive(Context context, Intent intent) {
NetworkInfo info = intent.getParcelableExtra(ConnectivityManager.EXTRA_NETWORK_INFO);
if( (info.getState()== State.DISCONNECTING) && (info.getType() == ConnectivityManager.TYPE_WIFI) ) {
//send logout
}
But it looks like at that time it's already too late. My logout message doesn't go through.
Is there a better way?
[Update 1]
I also tried:
if( (info.getDetailedState()== DetailedState.DISCONNECTING) && connectionTypeOK ) {
[Update 2 - SOLUTION]
The solution is, as stated below, using a combination of receiving the RSSI_CHANGED_ACTION and WIFI_STATE_CHANGED_ACTION broadcasts to monitor the signal strength and the WIFI_STATE_DISABLING events respectively. When this happens, I send my logout request. This works exactly as I needed. Thanks!!
You could try to implement a variable "heartbeat" function, by using WifiManager to detect changes in signal strength. Here you can find some related code, btw.
Now, once you receive a RSSI_CHANGED notification, according to the corresponding signal strength, you will update the frequency of your app's "heartbeats" to the server: if the signal is strong, you will only need to notify the server infrequently that the app is alive. Once the signal becomes week, however, just like adrenaline kicking in for a real live being, so should your app notify the server more frequently. If the signal's strength recovers, you'll send a specific message to let the server know everything is all right again; if, however, the server does not receive this message in a certain period of time and the "heartbeat" stops - your app ceases notifications for that amount of time - then the server logs it out until receiving from it again.
If you're based on TCP connections, the server should know when a session disconnects unexpectedly - it will get an RST or FIN packet, depending on the router configuration between the client and server.
There's no need to do anything from the client's point of view - TCP connections are designed so you can know when they're interrupted.
Why don't you have the server regularly ping the client, at certain intervals, and just log out if it doesn't get a response? Trying to make this happen through client side will be cumbersome.
A better way is not to have sessions at all, if possible.
Why is it a problem if the user doesn't log out?
Maybe this is a long shot.. but why don't you use Google push notifications to start an activity if wifi is on. That would tell the server that the phone is "online". If that doesn't happen in X seconds or 1 minute ou whatever, redirect it to somewhere else.
I would implement a handler on the server that handles when the client is not able to receive a message. After each message the phone could send a message back to the server saying it successfully received the message.
are you looking for a good way for users to send / receive data after a disconnection?
HTML5 has a local storage (with a good file size too) so if a user is attempting a huge form, you first save it locally and then attempt to send it to server. if failed when the user loads the page again, you can first check if the file has some content, and if so, you can send that data, clear the content and proceed accordingly.
may be this will help you out http://www.html5rocks.com/tutorials/appcache/beginner/
or look at the local storage tutorial: http://www.youtube.com/watch?v=h0uZIljjElo
using this you could save frequent status data and modify it on the fly.
and Android should support HTML5 too.
I have a simple app that periodically sends HTTP_GET requests to a server. When sending requests over 3G, I noticed that the requests sometimes time out (and the server-side logging shows that it NEVER receives the request either).
After trying out different combinations I found one consistant pattern when this problem occures (it times out after every 5-15 successful requests).
- TelephonyRegistry: notifyDataConnection() state=2isDataConnectivityPossible()true, reason=null
- TelephonyRegistry: broadcastDataConnectionStateChanged() state=CONNECTEDtypes=default supl, interfaceName=rmnet0
- NetworkLocationProvider: onDataConnectionStateChanged 3
According to Google, NetworkLocationProvider is changed to 'DATA_SUSPENDED', which implies "connection is up, but IP traffic is temporarily unavailable". (see TelephonyManager). On the situations where HTTP_GET requests succeeds, the state is changed to '8'. My app doesn't use the location manage and I've shut down every other non-critical app from running!
I want to know:
What is the cause of this issue? Why does the connection status go to DATA_SUSPENDED?
Is it possible to avoid/overcome this problem?
Any help/insight into this is much appreciated! Thanks in advance!
I have the same problem with my app running on an Huawei IDEOS X3 with Android 2.3.5. The app sends data each minute to a server using HttpClient.
Using logcat I can see that the data connection is lost and then reestablished after a short while. Previously my app stopped working since it tried to send data without a connection causing an exception which was not properly handed.
I don't know the reason for the intermittently dropped data connection but I now handle the situation by checking if there is a data connection prior to sending the data. In my case it does not matter if some data is never sent. If it was important to avoid data loss, I could buffer the data and send it once the connection was back.
public Boolean isDataConnection() {
TelephonyManager tm = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
return tm.getDataState() == TelephonyManager.DATA_CONNECTED;
}