Develop Reference

Why do multiple parallel invocations of NetworkManager.addToQueueAndWait interfere with each other?

Multiple invocations to the jsonRequest() method from different Threads (Timer-1 and EDT) do interfere with each other and even one call returns the result of a previous invocation
My CodeNameOne application uses a background Thread (Timer-1) to retrieve and display data from a REST service every second and it allows the user to issue commands that also issue REST calls from the EDT thread.
private Map<String, Object> jsonRequest(String url, String body, String cmd, int timeoutMs) {
long startTs = System.currentTimeMillis();
try {
request = new ConnectionRequest();
request.setReadResponseForErrors(true);
// request.setTimeout(timeoutMs);
// Shai: Timeout in Codename One is currently limited to connection timeout and
// doesn't apply to read timeout so once a connection is made it will last
request.setHttpMethod(cmd);
request.setPost(cmd.equalsIgnoreCase("POST") || cmd.equalsIgnoreCase("PUT") || cmd.equalsIgnoreCase("PATCH"));
if (body != null) {
request.addRequestHeader("Accept", "application/json");
request.setContentType("application/json");
request.setRequestBody(body);
request.setWriteRequest(true);
}
request.setUrl(url);
NetworkManager.getInstance().addToQueueAndWait(request);
long duration = System.currentTimeMillis() - startTs;
Log.p(cmd + ": " + url + " " + duration + " ms");
if (request.getResponseCode() >= 400 || request.getResponseData() == null) {
Log.p("responseCode=" + request.getResponseCode() + " responseData=" + request.getResponseData());
return null;
}
Log.p(cmd + ": " + url + " " + new String(request.getResponseData()));
Map<String, Object> result = new JSONParser().parseJSON(new InputStreamReader(new ByteArrayInputStream(request.getResponseData()), "UTF-8"));
return result;
} catch (Exception e) {
problemHandler.handle(cmd, url, e);
}
return null;
}
Actually result of multiple invocations get mixed up.
I would expect that each call to addToQueueAndWait() waits for the right result and returns just when the result is there.
I observed this problem to happen much more often on Android than on iOS or the simulator

I doubt that's what you are seeing. I see that request is defined in the class level as a variable so I'm guessing you are seeing a typical race condition where the request variable gets replaced while one is sent and by the time you reach the parsing it's a different object.
There is no need to use a thread for polling as networking already runs on a separate thread (or more this is usually determined in the init(Object) method).
I would suggest using a timer for a single invocation that's invoked after the response finishes.
A better approach would be websockets though: https://www.codenameone.com/blog/introducing-codename-one-websocket-support.html
With websockets the server can push out an update notification. This will save you the need to constantly poll the server. It saves on device battery life and resources on server/device.

How do you synchronize android clients with a python server?

I have a python server and about 10 android clients, using sockets. It is really important that when the server sends a message, all clients receive it at the same time (say 1/10th of a second of difference).
But the connection is over Wifi, and some devices get the message later than others, which gives a very messy result. I don't want to get the latency of every device because this is a very unreliable approach. I want something as accurate as possible.
For example, in FPS games, it is common to have a countdown at the start of the round, and every player can start playing at the same time. What kind of logic lies behind this?
As for what my code currently looks like:
I use a BufferedReader in android to read every line sent by the server. The server is a console application in which you can type a message, and when you press enter, every listed client receives it with a new thread for every client.
java method receiving messages:
private void readMessage() throws IOException {
String data;
while ((data = mBufferedReader.readLine()) != null) {
data = data.toUpperCase();
if (data.startsWith("POSITION")) {
String[] splitData = data.split("/");
Log.d(Constants.TAG, splitData[1]);
mMainActivity.setDevicePosition(Integer.parseInt(splitData[1]));
} else {
String message = data.substring(data.indexOf('/') + 1, data.length());
int devices = Integer.parseInt(data.substring(0, data.indexOf('/')));
if (message.length() >= devices) {
message += " ";
} else {
int difference = devices - message.length();
for (int i = 0; i < difference; i++) {
message += " ";
}
}
mMainActivity.printMessage(message);
}
}
}
python line :
for cl in clients_list:
start_new_thread(send_message_thread, (cl, message,))

Problems when sending a continuous stream of data over BLE

I'm wondering if anybody can help me figure out what is causing the data I am sending to become corrupt.
My setup is currently an Arduino pro mini with a HM-10 bluetooth module connected (I have also tried HM-11 Module too) and an Android application to receive the bluetooth data.
Module setup: http://letsmakerobots.com/node/38009
If I send data with big enough intervals then the data is fine, but if I send the data continuously I see messages getting mixed up and lost. To test this I send "$0.1,0.2,0.3,0.4,0.5" to the Android application from the Arduino, sometimes the stream of data appears to send fine but other times it is really quite scrambled. Please see the below graphs that demonstrate this:
Good case:
Bad case:
Arduino code:
String inputString = ""; //Hold the incoming data.
boolean stringComplete = false; //Determines if the string is complete.
boolean realtime = false;
void setup()
{
Serial.begin(9600);
delay(500);
Serial.print("AT+START");
delay(500);
}
void loop()
{
if(stringComplete)
{
if(inputString.equals("rStart"))
{
Serial.println("$startACK");
realtime = true;
}
else if(inputString.equals("stop"))
{
Serial.println("$stopACK");
realtime = false;
}
else{
Serial.print(inputString);
}
inputString = "";
stringComplete = false;
}
if(realtime)
{
Serial.println("$0.1,0.2,0.3,0.4,0.5,0.6");
delay(10);
}
}
void serialEvent() {
while (Serial.available())
{
// get the new byte:
char inChar = (char)Serial.read();
if (inChar == '\n')
{
stringComplete = true;
}
else
{
inputString += inChar;
}
}
}
The Android side just receives the data and then parses it in an IntentService:
#Override
protected void onHandleIntent(Intent intent) {
//Incoming command.
String rawData = intent.getStringExtra(DataProcessingIntentService.REQUEST);
//Append our new data to our data helper.
Log.i(this.getClass().getName(), "Previous Raw: (" + DataProcessingHelper.getInstance().getData() + ")");
DataProcessingHelper.getInstance().appendData(rawData);
Log.i(this.getClass().getName(), "New Raw: (" + DataProcessingHelper.getInstance().getData() + ")");
commandStartIndex = DataProcessingHelper.getInstance().getData().indexOf("$");
commandEndIndex = DataProcessingHelper.getInstance().getData().indexOf("\n");
//Set this as the data starting point.
if(commandStartIndex != -1){
DataProcessingHelper.getInstance().offsetData(commandStartIndex);
}
//Ensure that a command has been found and that the end index is after the starting index.
if(commandStartIndex != -1 && commandEndIndex > commandStartIndex){
//Remove the command structure from the command.
command = DataProcessingHelper.getInstance().getData().substring(commandStartIndex+1, commandEndIndex-1); //Remove the \r\n end command.
DataProcessingHelper.getInstance().offsetData(commandEndIndex+1);
if(command.length() > 1){
//Split the data out of the comand.
splitData = command.split(",");
Log.i(this.getClass().getName(), "Broadcasting the processed data. (" + command + ")");
//Broadcast data.
Intent broadcastIntent = new Intent();
broadcastIntent.setAction(DataProcessingIntentService.RESPONSE);
broadcastIntent.addCategory(Intent.CATEGORY_DEFAULT);
broadcastIntent.putExtra(DataProcessingIntentService.RESPONSE, splitData);
sendBroadcast(broadcastIntent);
}else{
Log.e(this.getClass().getName(), "Command is less than 1 character long!");
}
}
}
Thank you for any help!

I have now figured out what was causing this problem. It appears that BLE only supports a maximum of 20 bytes per a transaction. The time between these transactions is different depending on what you are using. I'm currently using notifications which means that I can send 20 bytes every 7.5 milliseconds maximum. I have opted for 10 milliseconds to be safe. I will now need to look into breaking up packets into 20 bytes maximum to ensure no data corruption.

Connecting to existing Google Chromecast Session from Android (for generic remote control)

I am creating a generic Chromecast remote control app. Most of the guts of the app are already created and I've managed to get Chromecast volume control working (by connecting to a Chromecast device along side another app that is casting - YouTube for example).
What I've having difficult with is performing other media commands such as play, pause, seek, etc.
Use case example:
1. User opens YouTube on their android device and starts casting a video.
2. User opens my app and connects to the same Chromecast device.
3. Volume control from my app (works now)
4. Media control (play, pause, etc) (does not yet work)
I found the Cast api reference that explains that you can sendMessage(ApiClient, namespace, message) with media commands; however the "message" (JSON) requires the sessionId of the current application (Youtube in this case). I have tried the following, but the connection to the current application always fails; status.isSuccess() is always false:
Cast.CastApi
.joinApplication(mApiClient)
.setResultCallback(
new ResultCallback<Cast.ApplicationConnectionResult>() {
#Override
public void onResult(
Cast.ApplicationConnectionResult result) {
Status status = result.getStatus();
if (status.isSuccess()) {
ApplicationMetadata applicationMetadata = result
.getApplicationMetadata();
sessionId = result.getSessionId();
String applicationStatus = result
.getApplicationStatus();
boolean wasLaunched = result
.getWasLaunched();
Log.i(TAG,
"Joined Application with sessionId: "
+ sessionId
+ " Application Status: "
+ applicationStatus);
} else {
// teardown();
Log.e(TAG,
"Could not join application: "
+ status.toString());
}
}
});
Is is possible to get the sessionId of an already running cast application from a generic remote control app (like the one I am creating)? If so, am I right in my assumption that I can then perform media commands on the connected Chromecast device using something like this:
JSONObject message = new JSONObject();
message.put("mediaSessionId", sessionId);
message.put("requestId", 9999);
message.put("type", "PAUSE");
Cast.CastApi.sendMessage(mApiClient,
"urn:x-cast:com.google.cast.media", message.toString());
Update:
I have tried the recommendations provided by #Ali Naddaf but unfortunately they are not working. After creating mRemoteMediaPlayer in onCreate, I also do requestStatus(mApiClient) in the onConnected callback (in the ConnectionCallbacks). When I try to .play(mApiClient) I get an IllegalStateException stating that there is no current media session. Also, I tried doing joinApplication and in the callback performed result.getSessionId; which returns null.

A few comments and answers:
You can get the sessionId from the callback of launchApplication or joinApplication; in the "onResult(result)", you can get the sessionId from: result.getSessionId()
YouTube is still not on the official SDK so YMMV, for apps using official SDK, you should be able to use the above approach (most of it)
Why are you trying to set up a message yourself? Why not building a RemoteMediaPlayer and using play/pause that is provided there? Whenever you are working with the media playback through the official channel, always use the RemoteMediaPlayer (don't forget to call requestStatus() on it after creating it).

Yes it is possible , First you have to save sesionId and CastDevice device id
and when remove app from background and again open app please check is there sessionId then call bello line.
Cast.CastApi.joinApplication(apiClient, APP_ID,sid).setResultCallback(connectionResultCallback);
if you get success result then need to implement further process in connectionResultCallback listener.
//Get selected device which you selected before
#Override
public void onRouteAdded(MediaRouter router, MediaRouter.RouteInfo route) {
// Log.d("Route Added", "onRouteAdded");
/* if (router.getRoutes().size() > 1)
Toast.makeText(homeScreenActivity, "'onRouteAdded :: " + router.getRoutes().size() + " -- " + router.getRoutes().get(1).isSelected(), Toast.LENGTH_SHORT).show();
else
Toast.makeText(homeScreenActivity, "'onRouteAdded :: " + router.getRoutes(), Toast.LENGTH_SHORT).show();*/
if (router != null && router.getRoutes() != null && router.getRoutes().size() > 1) {
// Show the button when a device is discovered.
// Toast.makeText(homeScreenActivity, "'onRouteAdded :: " + router.getRoutes().size() + " -- " + router.getRoutes().get(1).isSelected(), Toast.LENGTH_SHORT).show();
mMediaRouteButton.setVisibility(View.VISIBLE);
titleLayout.setVisibility(View.GONE);
castName.setVisibility(View.VISIBLE);
selectedDevice = CastDevice.getFromBundle(route.getExtras());
routeInfoArrayList = router.getRoutes();
titleLayout.setVisibility(View.GONE);
if (!isCastConnected) {
String deid = MyPref.getInstance(homeScreenActivity).readPrefs(MyPref.CAST_DEVICE_ID);
for (int i = 0; i < routeInfoArrayList.size(); i++) {
if (routeInfoArrayList.get(i).getExtras() != null && CastDevice.getFromBundle(routeInfoArrayList.get(i).getExtras()).getDeviceId().equalsIgnoreCase(deid)) {
selectedDevice = CastDevice.getFromBundle(routeInfoArrayList.get(i).getExtras());
routeInfoArrayList.get(i).select();
ReSelectedDevice(selectedDevice, routeInfoArrayList.get(i).getName());
break;
}
}
}
}
}
//Reconnect google Api Client
public void reConnectGoogleApiClient() {
if (apiClient == null) {
Cast.CastOptions apiOptions = new
Cast.CastOptions.Builder(selectedDevice, castClientListener).build();
apiClient = new GoogleApiClient.Builder(this)
.addApi(Cast.API, apiOptions)
.addConnectionCallbacks(reconnectionCallback)
.addOnConnectionFailedListener(connectionFailedListener)
.build();
apiClient.connect();
}
}
// join Application
private final GoogleApiClient.ConnectionCallbacks reconnectionCallback = new GoogleApiClient.ConnectionCallbacks() {
#Override
public void onConnected(Bundle bundle) {
// Toast.makeText(homeScreenActivity, "" + isDeviceSelected(), Toast.LENGTH_SHORT).show();
try {
String sid = MyPref.getInstance(homeScreenActivity).readPrefs(MyPref.CAST_SESSION_ID);
String deid = MyPref.getInstance(homeScreenActivity).readPrefs(MyPref.CAST_DEVICE_ID);
if (sid != null && deid != null && sid.length() > 0 && deid.length() > 0)
Cast.CastApi.joinApplication(apiClient, APP_ID, sid).setResultCallback(connectionResultCallback);
isApiConnected = true;
} catch (Exception e) {
}
}
#Override
public void onConnectionSuspended(int i) {
isCastConnected = false;
isApiConnected = false;
}
};

Store Battery Level Status In a txt File

I am a New B to Android. I have been Able to get the Battery Status/Level with the Following Code:
private void BattStatus() {
BroadcastReceiver batteryLevelReceiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
context.unregisterReceiver(this);
int rawlevel = intent.getIntExtra("level", -1);
int scale = intent.getIntExtra("scale", -1);
int level = -1;
if (rawlevel >= 0 && scale > 0) {
level = (rawlevel * 100) / scale;
}
batteryLevel = level;
BattStatus.setText("Battery Level : " + batteryLevel + "%");
}
};
IntentFilter batteryLevelFilter = new IntentFilter(Intent.ACTION_BATTERY_CHANGED);
registerReceiver(batteryLevelReceiver, batteryLevelFilter);
}
I would Like to Store the Battery Level In A text file (Using a thread). Code :
public final Runnable DBThread = new Runnable() {
String AllInfo = batteryLevel+"%"+" , "+new SimpleDateFormat("HH:mm , dd.MM.yy ").format(new Date());
public void run() {
try {
Log.d("DBThread","Battery :"+batteryLevel);
Log.d("DBThread","Updating DB");
myDbHelper.CreateAndWriteFile(sdDir+"/", AllInfo );
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
mHandler.postAtTime(this, SystemClock.uptimeMillis() + 2000);
Log.d("DBThread","Updated DB");
Log.d("DBThread",AllInfo);
}
Unfortunately the Battery Status/Level returns 0% in the text file, when I test it using the Log function in the thread it returns the correct value.
Please could some one be so kind to tell me what I am doing wrong or what I am not doing, and maybe provide me with a code snippet as I am new to Development.And Sorry If My Post is incorrect First timer on Stack Overflow :)
Thank you very much!

This is not a Thread. This is a Runnable, which is a piece of code that is made to run in a Thread.
In your case, it runs in the handler thread, most likely the UI Thread.
You probably start your thread before receiving the battery status, hence writing the default value (0) to the file.
You don't need a thread for that. You can write to the file immediately after your receive the broadcast, in the onReceive method.
Edit
There are a few things that don't work in your code. You unregister the broadcast receiver, hence you don't receive the battery level after the first time.
You write the batteryLevel value without knowing if it has indeed been modified
You write every 2 seconds without knowing there has been a change.
I would suggest that you don't unregister the BR, so you receive all battery level change. Then, in the onReceive, you append to the file the date and new value.