Develop Reference

Flutter/Dart UDP multicast send from iOS not receiving on Android

With this setup, I've been able to get two android phones to send and receive UDP broadcasts. I can also use this setup to send a UDP broadcast from a physical Android device to an iPhone.
However, my problem is that it doesn't seem to work the other way around. The send function is ran on the iPhone, and the receive function is being run on the Android phone. The Android phone never gets the broadcast. It seems like something is wrong with the iPhone's sending function. Here's the setup:
The Android side that has worked for me before:
const port = 37069;
const address = '224.0.0.1';
void receive() async {
final socket = await RawDatagramSocket.bind(address, port);
socket.multicastHops = 1;
socket.broadcastEnabled = true;
socket.writeEventsEnabled = true;
socket.listen((RawSocketEvent event) {
print("still listening...");
final packet = socket.receive();
print("The packet was $packet");
print("It came from ${packet?.address}");
});
}
and this is the iPhone side, that seems to be the problem. I'm not getting errors, so I'm wondering if there are any permissions in the Info.plist file that need to be added?
void broadcast() {
// for the iphone
RawDatagramSocket.bind(address, port).then((RawDatagramSocket socket) {
socket.multicastLoopback = false;
socket.broadcastEnabled = true;
socket.readEventsEnabled = true;
for (int i = 0; i < 150; i++) {
socket.send("Sent #$i".codeUnits, InternetAddress(address), port);
print("sent $i");
}
socket.close();
});
}
I've tested this same setup in my project, and it has worked in the following situations:
Android -> Android
Android -> iOS
but, iOS -> Android doesn't work. When I run the app, I can see that the iPhone is indeed sending the data, but the Android isn't receiving anything. Is the Android side the problem? What am I doing wrong?

I ended up using a package called Bonsoir to achieve what I wanted to.
It lets you broadcast and receive network services, and I'm pretty sure its the same underlying technology as household programs like Airplay and Google Casting. It's also very reliable and simple to use.
To send a certain string, I passed in a string argument in the form of a dictionary into the attributes attribute within the BonsoirService class.
The package can be found here.

Android call method but don't work on wifi but work on gprs

we work with xamarin android and visual studio 2015.
we have an app who works since several months fine :)
This app when it starts call a webservice for to retrieve some data in json format.
All work fine, but last week we have a problem and we are COMPLETY lost about it !
Since last week, for one device when it call the web service we receive this error in the catch exception :
unable to read data from the transport connection Connection reset by peer ...
Here is it the method on the device who call the WS:
public override HttpResult ExecuteGet(Uri target)
{
var client = new HttpClient();
client.MaxResponseContentBufferSize = 25600000;
try
{
var response = client.GetAsync(target).Result;
if (response.IsSuccessStatusCode)
{
var content = response.Content.ReadAsStringAsync().Result;
return new HttpResult(content, null, null);
}
return new HttpResult(null, " ERROR MESSAGE ", response.StatusCode.ToString());
}
catch (Exception e)
{
return new HttpResult(null, " ERROR MESSAGE", e.Message);
}
}
well, now with the same device if we stop the wifi and call the webservice in GPRS that work.
Also we have two wifi, we also have noticed if the device connect on the second wifi and try to call the web service => that's work !
After talk with some colleague, they tell me to look to update my android version of the device , or wifi app on the device but for me the first thing we need to do will be to compare wifi 1 and wifi 2.
My question is, how i can compare two wifi ?
All suggestion are welcome because we search and we find nothing ...
Thanks for all guys that's really great to share your knowledge ...

Android 4.3: How to connect to multiple Bluetooth Low Energy devices

My Question is: Can Android 4.3 (client) have active connections with multiple BLE devices (servers)? If so, how can I achieve it?
What I did so far
I try to evaluate what throughput you can achieve using BLE and Android 4.3 BLE API. In addition I also try to find out how many devices can be connected and active at the same time. I use a Nexus 7 (2013), Android 4.4 as master and TI CC2540 Keyfob as slaves.
I wrote a simple server software for the slaves, which transmits 10000 20Byte packets through BLE notifications. I based my Android App on the Application Accelerator from the Bluetooth SIG.
It works well for one device and I can achieve around 56 kBits payload throughput at a Connection Interval of 7.5 ms. To connect to multiple slaves I followed the advice of a Nordic Employee who wrote in the Nordic Developer Zone:
Yes it's possible to handle multiple slaves with a single app. You would need to handle each slave with one BluetoothGatt instance. You would also need specific BluetoothGattCallback for each slave you connect to.
So I tried that and it partly works. I can connect to multiple slaves. I can also register for notifications on multiple slaves. The problem begins when I start the test. I receive at first notifications from all slaves, but after a couple Connection Intervals just the notifications from one device come trough. After about 10 seconds the other slaves disconnect, because they seem to reach the connection time-out. Sometimes I receive right from the start of the test just notifications from one slave.
I also tried accessing the attribute over a read operation with the same result. After a couple of reads just the answers from one device came trough.
I am aware that there are a few similar questions on this forum: Does Android 4.3 support multiple BLE device connections?, Has native Android BLE GATT implementation synchronous nature? or Ble multiple connection. But none of this answers made it clear for me, if it is possible and how to do it.
I would be very grateful for advice.

I suspect everyone adding delays is just allowing the BLE system to complete the action you have asked before you submit another one. Android's BLE system has no form of queueing. If you do
BluetoothGatt g;
g.writeDescriptor(a);
g.writeDescriptor(b);
then the first write operation will immediately be overwritten with the second one. Yes it's really stupid and the documentation should probably actually mention this.
If you insert a wait, it allows the first operation to complete before doing the second. That is a huge ugly hack though. A better solution is to implement your own queue (like Google should have). Fortunately Nordic have released one for us.
https://github.com/NordicSemiconductor/puck-central-android/tree/master/PuckCentral/app/src/main/java/no/nordicsemi/puckcentral/bluetooth/gatt
Edit: By the way this is the universal behaviour for BLE APIs. WebBluetooth behaves the same way (but Javascript does make it easier to use), and I believe iOS's BLE API also behaves the same.

Re visting the bluetooth-lowenergy problem on android: I am still using delays.
The concept: after every major action that provokes the BluetoothGattCallback (e.g. conenction, service discovery, write, read) a dealy is needed. P.S. have a look at Google example on BLE API level 19 sample for connectivity to understand how Broadcasts should be sent and get some general understanding etc...
Firstly, scan (or scan) for BluetoothDevices, populate the connectionQueue with desired devices and call initConnection().
Have a look on the following example.
private Queue<BluetoothDevice> connectionQueue = new LinkedList<BluetoothDevice>();
public void initConnection(){
if(connectionThread == null){
connectionThread = new Thread(new Runnable() {
#Override
public void run() {
connectionLoop();
connectionThread.interrupt();
connectionThread = null;
}
});
connectionThread.start();
}
}
private void connectionLoop(){
while(!connectionQueue.isEmpty()){
connectionQueue.poll().connectGatt(context, false, bleInterface.mGattCallback);
try {
Thread.sleep(250);
} catch (InterruptedException e) {}
}
}
Now if all is good, you have made connections and BluetoothGattCallback.onConnectionStateChange(BluetoothGatt gatt, int status, int newState) has been called.
public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
switch(status){
case BluetoothGatt.GATT_SUCCESS:
if (newState == BluetoothProfile.STATE_CONNECTED) {
broadcastUpdate(BluetoothConstants.ACTION_GATT_CONNECTED, gatt);
}else if(newState == BluetoothProfile.STATE_DISCONNECTED){
broadcastUpdate(BluetoothConstants.ACTION_GATT_DISCONNECTED, gatt);
}
break;
}
}
protected void broadcastUpdate(String action, BluetoothGatt gatt) {
final Intent intent = new Intent(action);
intent.putExtra(BluetoothConstants.EXTRA_MAC, gatt.getDevice().getAddress());
sendBroadcast(intent);
}
P.S. sendBroadcast(intent) might need to be done like this:
Context context = activity.getBaseContext();
context.sendBroadcast(intent);
Then the broadcast is received by BroadcastReceiver.onReceive(...)
public BroadcastReceiver myUpdateReceiver = new BroadcastReceiver(){
#Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
if(BluetoothConstants.ACTION_GATT_CONNECTED.equals(action)){
//Connection made, here you can make a decision: do you want to initiate service discovery.
// P.S. If you are working with multiple devices,
// make sure that you start the service discovery
// after all desired connections are made
}
....
}
}
After doing whatever you want in the broadcast receiver, here is how I continue:
private Queue<BluetoothGatt> serviceDiscoveryQueue = new LinkedList<BluetoothGatt>();
private void initServiceDiscovery(){
if(serviceDiscoveryThread == null){
serviceDiscoveryThread = new Thread(new Runnable() {
#Override
public void run() {
serviceDiscovery();
serviceDiscoveryThread.interrupt();
serviceDiscoveryThread = null;
}
});
serviceDiscoveryThread.start();
}
}
private void serviceDiscovery(){
while(!serviceDiscoveryQueue.isEmpty()){
serviceDiscoveryQueue.poll().discoverServices();
try {
Thread.sleep(250);
} catch (InterruptedException e){}
}
}
Again, after a successful service discovery, BluetoothGattCallback.onServicesDiscovered(...) is called. Again, I send an intent to the BroadcastReceiver (this time with different action String) and it is now that you can start reading, writing and enabling notifications/indications...
P.S. If you are working with multiple devices, make sure that you start the reading, writing etc... stuff after all devices have reported that their services have been discovered.
private Queue<BluetoothGattCharacteristic> characteristicReadQueue = new LinkedList<BluetoothGattCharacteristic>();
private void startThread(){
if(initialisationThread == null){
initialisationThread = new Thread(new Runnable() {
#Override
public void run() {
loopQueues();
initialisationThread.interrupt();
initialisationThread = null;
}
});
initialisationThread.start();
}
}
private void loopQueues() {
while(!characteristicReadQueue.isEmpty()){
readCharacteristic(characteristicReadQueue.poll());
try {
Thread.sleep(BluetoothConstants.DELAY);
} catch (InterruptedException e) {}
}
// A loop for starting indications and all other stuff goes here!
}
BluetoothGattCallback will have all your incoming data from the BLE sensor. A good practice is to send a broadcast with the data to your BroadcastReceiver and handle it over there.

I am developing an app with BLE features myself. The way I managed to connect to multiple devices and turn on notifications was to implement delays.
So I make a new thread (in order not to block UI thread) and in the new thread connect and turn on notifications.
For example, after BluetoothDevice.connectGatt(); call Thread.sleep();
And add the same delay for read/write and enable/dissable notifications.
EDIT
Use wait like this so that Android dindn't reaise ANR
public static boolean waitIdle() {
int i = 300;
i /= 10;
while (--i > 0) {
if (true)
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
return i > 0;
}

Unfortunately notifications in the current Android BLE stack are a bit buggy. There are some hardcoded limits and I've found some stability issues even with a single device. (I read at one point that you could only have 4 notifications... not sure if that's across all devices or per device. Trying to find the source for that info now.)
I would try switching to a polling loop (say, poll the items in question 1/sec) and seeing if you find your stability increases. I would also consider switching to a different slave device (say a HRM or the TI SensorTag) to see if there is perhaps an issue with the slave-side code (unless you can test that against iOS or another platform and confirm it isn't part of the issue).
Edit: Reference for notification limitation

Rain is right in his answer, you need delays for pretty much everything when you work with BLE in Android. I developed several apps with it and it is really necessary. By using them you avoid a lot of crashes.
In my case, I use delays after every read/write command. Doing so, you ensure you receive the response from the BLE device almost always. I do something like this: (of course everything is done in a separate thread to avoid to much work on the main thread)
readCharacteristic(myChar);
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
myChar.getValue();
or:
myChar.setValue(myByte);
writeCharacteristic(myChar);
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
This is really useful when you read/write several characteristics in a row... As Android is enough fast to execute the commands almost instantly, if you don't use a delay between them you may get errors or incoherent values...
Hope it helps even if it is not exactly the answer to your question.

How to connect to Bluetooth SPP using dot42?

After reading the dot42 comments and trolling Java examples I managed to setup a Bluetooth connection but fail to open the connection. I cannot determine the problem. I followed the docs step by step.
My target device is a HTC Explorer running on 2.3 Gingerbread. Here is my code.
//Target 2.3 (Gingerbread)
[assembly: Application("dot42Application1")]
[assembly: UsesPermission(Android.Manifest.Permission.BLUETOOTH)]
[assembly: UsesPermission(Android.Manifest.Permission.BLUETOOTH_ADMIN)]
namespace dot42Application1
{
[Activity]
public class MainActivity : Activity
{
private TextView txStatus;
protected override void OnCreate(Bundle savedInstance)
{
base.OnCreate(savedInstance);
SetContentView(R.Layouts.MainLayout);
// Find UI controls
txStatus = FindViewById<TextView>(R.Ids.txStatus);
Intent enableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
var bt = BluetoothAdapter.GetDefaultAdapter();
if (bt != null) //If device has not Bluetooth this will be null
{
if (bt.IsEnabled()) //Is Bluetooth device enabled?
{
var BT_My_Addr = bt.Address; //Get the devices MAC
var BT_Bonded = bt.GetBondedDevices().ToList(); //Get a list of bonded devices- I bonded to a BT2TTL Board earlier.
txStatus.Text = BT_My_Addr + System.Environment.NewLine; //Shows my MAC on screen.
string BT_Remote_Address = string.Empty;
foreach (var BTDevice in BT_Bonded) //Just searchging for string in bonded list
{
if (BTDevice.Name.Contains("linvor"))
{
BT_Remote_Address = BTDevice.Address;
}
}
//Gets remote device
var BT_Remote_Device = bt.GetRemoteDevice(BT_Remote_Address);
//Create a RFCOMM Socket to remote device using popular UUID ofr BT Serial boards
var BTsocket = BT_Remote_Device.CreateInsecureRfcommSocketToServiceRecord(Java.Util.UUID.FromString("00001101-0000-1000-8000-00805F9B34FB"));
//Call anyway to make sure there is no discvoerry in the backgorund. It slows stuff down.
bt.CancelDiscovery();
//Exception here? Dont know why :(
BTsocket.Connect();
//Suppsoed to dump 0 to 99999 to my listening serial device but I never get this far.
var BT_Out = BTsocket.GetOutputStream();
for (int i = 0; i < 99999; i++)
{
BT_Out.Write(Encoding.ASCII.GetBytes(i.ToString()));
}
}
else
{
txStatus.Text = "Bluetooth is disabled :(";
}
}
}
}
And this is what it shows after the socket creation
and the error...
What am I doing wrong? :(

I seem to have solved the problem by analysing various code snippets on the internet. I think the problem was trying to do everything in the OnCreate method. The steps I followed are the following:
Created a button on the main view (MainActivity.xml) and attached a onClick method.
Moved all the code OUT of the OnCreate method. (I think this allows the application to fully initialise.) Created an event handler for the button with two methods.
The two methods are the same as the code I posted in my original question. Just they are separated out and called when the user clicks the button.
findBT() Gets the default adapter. Checks if Bluetooth is enabled if not does the intent filter. Or if it is it will cycle through the bonded list and match a device name and store the BluetoohDevice in a variable. This is another thing that is different from my code. I do not use GetRemoteDevice I just assign the device from the BondedList to my global variable.
openBT() creates the RFCOMM socket (this did not work with unsecure - it threw an exception but using the secure method worked!)
You have to pair to the remote device using the Androids Bluetooth control panel. This code will not scan or connect to devices that are not paired. It will just throw null exceptions.
Also I left the target SDK 2.3.x but I am using the 4.x API.
-Disclosure. I am not a seasoned Android developer and just learning about the life cycle of Java applications in the Android context. I hope this can help other C# developers trying to do the same.

How to prevent name caching and detect bluetooth name changes on discovery

I'm writing an Android app which receives information from a Bluetooth device. Our client has suggested that the Bluetooth device (which they produce) will change its name depending on certain conditions - for the simplest example its name will sometimes be "xxx-ON" and sometimes "xxx-OFF". My app is just supposed to seek this BT transmitter (I use BluetoothAdapter.startDiscovery() ) and do different things depending on the name it finds. I am NOT pairing with the Bluetooth device (though I suppose it might be possible, the app is supposed to eventually work with multiple Android devices and multiple BT transmitters so I'm not sure it would be a good idea).
My code works fine to detect BT devices and find their names. Also, if the device goes off, I can detect the next time I seek, that it is not there. But it seems that if it is there and it changes name, I pick up the old name - presumably it is cached somewhere. Even if the bluetooth device goes off, and we notice that, the next time I detect it, I still see the old name.
I found this issue in Google Code: here but it was unclear to me even how to use the workaround given ("try to connect"). Has anyone done this and had any luck? Can you share code?
Is there a simple way to just delete the cached names and search again so I always find the newest names? Even a non-simple way would be good (I am writing for a rooted device).
Thanks

I would suggest 'fetchUuidsWithSdp()'. It's significance is that, unlike the similar getUuids() method, fetchUuidsWithSdp causes the device to update cached information about the remote device. And I believe this includes the remote name as well as the SPD.
Note that both the methods I mentioned are hidden prior to 4.0.3, so your code would look l ike this:
public static void startServiceDiscovery( BluetoothDevice device ) {
// Need to use reflection prior to API 15
Class cl = null;
try {
cl = Class.forName("android.bluetooth.BluetoothDevice");
} catch( ClassNotFoundException exc ) {
Log.e(CTAG, "android.bluetooth.BluetoothDevice not found." );
}
if (null != cl) {
Class[] param = {};
Method method = null;
try {
method = cl.getMethod("fetchUuidsWithSdp", param);
} catch( NoSuchMethodException exc ) {
Log.e(CTAG, "fetchUuidsWithSdp not found." );
}
if (null != method) {
Object[] args = {};
try {
method.invoke(device, args);
} catch (Exception exc) {
Log.e(CTAG, "Failed to invoke fetchUuidsWithSdp method." );
}
}
}
}
You'll then need to listen for the BluetoothDevice.ACTION_NAME_CHANGED intent, and extract BluetoothDevice.EXTRA_NAME from it.
Let me know if that helps.