Develop Reference

Android only: C# .net-MAUI, not Xamarin(!), sending UDP?

Situation:
VS 2022, 17.0.4
Maui App,
net6.0-android
AndroidManifest.xml contains also:
android.permission.INTERNET
android.permission.CHANGE_NETWORK_STATE
android.permission.ACCESS_WIFI_STATE
android.permission.CHANGE_WIFI_MULTICAST_STATE
android.permission.CHANGE_WIFI_STATE
Connected mobile Phone:
Samsung SM-G960F (Android 10.0 - API 29)
OS: Windows 11, latest patch.
All firewalls are down (for testing purpose only!)
While debugging the develop computer is only connected to a Wifi network; computers ethernet card is disabled.
Mobile phone is connected to this dev computer via USB cable (to be able to debug) and to the same Wifi network as the computer.
App starts and works fine, app can be debugged. No issue at all - except:
After the application is fully initialized and ready to accept user interactions -> Click on button -> Desired method is called -> Code is worked out -> The code should make a simple UDP call but it does not (or the packet does not reach the UDP listener due to missing configuration?).
The UDP receiver works fine and is capable to receive UDP packets.
My mobile phone and the UDP receiver app are using the same port.
I read/found already that in the previous cross-platform framework, means “Xamarin (Android SDK 12)”, some permissions must be set (I did, see above) and that the multicastlock must be set over the WifiManager …
I tried this in my MAUI app. But could not find anything guiding me nor figured it out by myself.
My MAUI sending code:
var dataToBeSend = "What ever ...";
var data = Encoding.UTF8.GetBytes(dataToBeSend);
var UdpClient = new UdpClient();
// UdpClient.Client.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.Broadcast, true);
UdpClient.ExclusiveAddressUse = false;
UdpClient.EnableBroadcast = true;
// UdpClient.Client.Bind(new IPEndPoint(IPAddress.Parse("255.255.255.255"), BroadcastPort));
// UdpClient.Client.Bind(new IPEndPoint(IPAddress.Any, BroadcastPort));
UdpClient.Send(data, data.Length, "255.255.255.255", BroadcastPort);
As said: very easy and straight forward.
Notice that I also tried binding UDP code …
So please can someone be so kind to guide me or give me a hint?
Thank you very much in advance!

ANSWER:
After two days I found a solution - and would like to share it because may be it helps someone else.
The code to make the UDP call msut be placed in a THREAD (not task!)
codesnippet:
var communication = new Communication();
var udpThread = new Thread(new ThreadStart(communication.FireUDPCall));
udpThread.Start();
The firewalls can stay turned on / active!

Connect to specific Bluetooth device with a click

I'm trying to connect to a specific device using my Android APP, until now what I was able to do is get the paired items doing this :
BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
Set < BluetoothDevice > pairedDevices = bluetoothAdapter.getBondedDevices();
if (pairedDevices.size() > 0) {
for (BluetoothDevice device: pairedDevices) {
mDeviceName.add(device.getName());
mDeviceMAC.add(device.getAddress());
}
}
bluetoothClass.setDeviceName(mDeviceName);
bluetoothClass.setDeviceMac(mDeviceMAC);
Where I get the MAC and the Device name of all of my paired devices. The thing that I would like to do is when I select one it connects to the Bluetooth device.
EXAMPLE
On a Samsung S4 when I turn on the Bluetooth it popups a Dialog whitch contains all of my paired devices and when I click on anyone it connects (I've i'm able to ...) so basically I want to do this, since now I've been getting the paired devices (I don't know if it's the best way to get that but it does) and then when user click on anyone it connects to the device.
It's something like this question but it's unfortunately unanswered.

It's impossible to give you an example within this format, so I have provided you
with a good sample and helpful links to help you understand the sample.
I recommend you follow the steps I have provided and then, when you have
specific problems, you can bring it here, with the code snippet you are having
difficulty with.
I recommend you use download this sample code:
http://developer.android.com/samples/BluetoothChat/index.html
If you haven't already, it's good to study this:
http://developer.android.com/reference/android/bluetooth/BluetoothDevice.html
This is a good tutorial and they have many tutorials:
http://www.tutorialspoint.com/android/android_bluetooth.htm
You will need the following permissions in your manifest:
<uses-permission android:name="android.permission.BLUETOOTH"/>
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>
This is one intent that is advisable to use, to check to see if BT is enabled:
if (!mBluetoothAdapter.isEnabled()) {
android.content.Intent enableIntent = new android.content.Intent(
android.bluetooth.BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableIntent, REQUEST_ENABLE_BT);
}
and to make your device discoverable to other devices:
if (mBluetoothAdapter.getScanMode() !=
android.bluetooth.BluetoothAdapter.SCAN_MODE_CONNECTABLE_DISCOVERABLE) {
android.content.Intent discoverableIntent =
new android.content.Intent(
android.bluetooth.BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
discoverableIntent.putExtra(
android.bluetooth.BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION,
300); // You are able to set how long it is discoverable.
startActivity(discoverableIntent);
}
As I mentioned in my answer here:
You can avoid using an intent to search for paired devices. When
connecting to a device that is not paired, a notification will pop up
asking to pair the devices. Once paired this message should not show
again for these devices, the connection should be automatic (according
to how you have written your program).
I use an intent to enable bluetooth, and to make my device
discoverable, I then set up my code to connect, and press a button to
connect. In your case, you will need to ensure your accessories are
discoverable also. In my case I use a unique UUID, and both devices
must recognise this to connect. This can only be used if you are
programming both devices, whether both are android or one android and
one other device type.
You will need to understand how to use sockets, this is how the devices communicate.
I recommend studying these two links:
http://developer.android.com/reference/android/bluetooth/BluetoothSocket.html
http://developer.android.com/reference/android/bluetooth/BluetoothServerSocket.html
Sockets are used to set up connections between devices. There will be a server socket and device sockets (determined by many factors, the programmer, the actual devices). The server socket listens for incoming connections, when a connection is accepted the devices connect, each with a simple socket.
I am not sure how much you know about threading.
The connection needs to be managed with threads:
http://developer.android.com/guide/components/processes-and-threads.html
http://android-developers.blogspot.com.au/2009/05/painless-threading.html
The connection between the devices is managed on threads separate from the User
Interface thread. This is to prevent the phone from locking up while it is
setting up, seeking and making a BT connection.
For instance:
AcceptThread - the thread that listens for a connection and accepts the connection (via the serversocket). This thread can run for an extended time waiting for a device to connect with.
ConnectThread - the thread that the device connecting to the server uses to connect to the serversocket.
ConnectedThread - this is the thread that manages the connection between both sockets.
Let me know if this helps you.

How to check if Samsung Gear 2 is paired with Android device programmatically?

I am using Tizen SDK for Wearable from samsung-gear site in order to communicate a provider android application with Samsung Gear 2 device. I am able to send notifications to gear and once I run the consumer application on gear 2, I am able to transfer data between the watch and my Android phone as well.
What I am trying to do is to check within the Android application if the phone is paired with Gear 2. Something as simple as creating a communication object using the accessory service and calling a method like isPaired()?:
CommunicationObject commObject = new CommunicationObject(Communication parameters);
// I am assuming some connection call like commObject.connect() should be invoked first
// where I can check for it's result afterwards such as
if(commObject.isPaired())
{
// do something
}
I think SDK examples such as consumer/provider application they provide on their site already assume that the device is paired, hence they show how to transfer data between phone and the gear watch. Yet I am seeking something as simple as asking the phone if it's paired with a gear device, which should be the prerequisite for transferring the data, which is done automatically by Samsung Gear Manager I believe right now.
Note: For the case of example provider/consumer applications, one can just check if any connection is available using the code in them. But the data transfer connection enabled only when I manually start the consumer app from the gear device, otherwise it acts like gear device is not paired even though it is.

I believe this is not the most popular topic these days so I will post what I came up with as an answer although I doubt anyone will need it, without being perfect, it's the closest way I could get to my goal using the available documentation.
I should also mention that this slide helped me stay on track as well.
In my solution, there must be an active 2-way connection between the gear widget(consumer/.wgt) and the host side application(provider/.apk) as in the example application provided by Samsung(Hello Accessory) at all times, at least during the time where I wanted to check for the pairing condition. The documentation refers to it as:
Hello Gear is a simple application that consists of:
Host-side application(provider) : HelloAccessoryProvider.apk
Wearable-side Application(consumer) : HelloAccessoryConsumer.wgt (Web app)
See that both sides have some xml configuration and Android requires specific permissions which are explained in detail in Hello Gear documentation.
This 2 way communication is provided by the Samsung Accessory Framework on the network layer(through Samsung Accessory Protocol, SAP) given that both sides implement the same Accessory Service Profile, again, configured via the xml files on both ends(service name, channel id etc.).
Android side implements the protocol as a service, extending the SAAgent abstract class. Then the widget on gear side application(.wgt) can invoke the SAAgent callbacks and provider/consumer communication is handled through SASocket objects claimed on both ends over the predefined channel in the xml configuration files.
Please note that this communication has to be initialized on both ends, in my case I had to open the widget application once on Gear(I believe there should be a way to start the gear widget via an intent or notification, somehow, but I could not find yet) after the Android application has started, here started means that SAAgent service is up and bound to an Activity, being eligible to receive callbacks and send state messages to the rest of the application via broadcasts. Such as the number of active connections, or any data transmission between the gear socket and Android application can be done this way.
Note that if you don't have to transfer data between the gear widget and the Android application, you may just be OK with the notifications. The only requirement to send notifications to the Gear from Android applications seems to be that the Gear is paired with your phone and connected via Bluetooth. Then you can just send an intent as explained in more detail here in Section 6. All you need should be the permission:
com.samsung.wmanager.ENABLE_NOTIFICATION
and some metadata definition in your ApplicationManifest.xml file explained in the same section.
<meta-data
android:name="master_app_packagename"
android:value="com.example.gearMasterApp"/>
<meta-data
android:name="app_notification_maxbyte"
android:value="300 "/>
And here is the sample code for intent, in order to send notifications to the Gear:
public static final String ALERT_NOTIFICATION =
“com.samsung.accessory.intent.action.ALERT_NOTIFICATION_ITEM”;
public static final int NOTIFICATION_SOURCE_API_SECOND = 3;
Bitmap bitmapImg;
// Put data to Intent
Intent myIntent = new Intent(ALERT_NOTIFICATION);
myIntent.putExtra("NOTIFICATION_PACKAGE_NAME", “com.example.gearApp”);
myIntent.putExtra("NOTIFICATION_VERSION", NOTIFICATION_SOURCE_API_SECOND);
myIntent.putExtra("NOTIFICATION_TIME", System.currentTimeMillis(););
myIntent.putExtra("NOTIFICATION_MAIN_TEXT", “Title Text”);
myIntent.putExtra("NOTIFICATION_TEXT_MESSAGE", ”Body text);
byte [] byteArray = convertResizeBitmapToByte(bitmapImg);
myIntent.putExtra("NOTIFICATION_APP_ICON", byteArray);
myIntent.putExtra("NOTIFICATION_LAUNCH_INTENT", “com.example.gearMasterApp”);
myIntent.putExtra("NOTIFICATION_LAUNCH_TOACC_INTENT", “com.example.gearSideApp”);
sendBroadcast(myIntent);
public byte[] convertResizeBitmapToByte(Bitmap bitmap){
Bitmap scBitmap = Bitmap.createScaledBitmap(bitmap, 75, 75, false);
ByteArrayOutputStream byteArrayStream = new ByteArrayOutputStream();
scBitmap.compress(Bitmap.CompressFormat.PNG, 50, byteArrayStream);
return byteArrayStream.toByteArray();
}
Once the notification is read on the gear side, you can receive the intent action along with some optional parameters:
Intent Action :
"com.samsung.accessory.intent.action.UPDATE_NOTIFICATION_ITEM"
This could be another approach to check active communication with the Gear and your phone, but there is no guarantee that the notification will be read and my case did require to keep the Gear communication optional in order to allow the Android application continue it's tasks even though there is no active connection with the Gear.
About the original question, where I asked for a way to detect if the Gear is paired or not, I tried listing paired Bluetooth devices using getBondedDevices() method of Android's BluetoothAdapter but it shows that your Gear is paired even when your Gear is turned off, which was not enough for my needs and I did not find it logical. It's true though once your device is turned back on.
I'm happy with the above solution since it was enough for my needs, therefore I will accept my own answer.

Android WiFi Direct Demo Issues

im testing the new technology wifi direct and im having some issues using
the wifi direct demo from the samples that come with the android-sdk.
So, I have two devices A and B, both with android 4.0.3.
First, from device A, I send a file to B. Nothing wrong here, B
receives the file.
Then A disconnects from B.
Now, from device B I try to send a file to A.
But the device that receives the file is B, instead of A.
To fix, i need to turn off and on both devices...
Also, sometimes when i click disconnect and try to
connect again, connection fails and i have to disable and
enable wifi direct...
Anyone else experiencing this?
Is it because the new technology is not mature yet or maybe
something wrong with my build/driver/etc or maybe this demoapp
doesnt support two-way sharing.
Any ideas and/or explanations would be apreciated.

When providing a WifiP2pConfig instance to the connect() function, you can set the groupOwnerIntent property of this configuration object as follows:
WifiP2pConfig config = new WifiP2pConfig();
config.deviceAddress = "..."; // insert ip here
config.groupOwnerIntent = 0;
config.wps.setup = WpsInfo.PBC;
manager.connect(..., config, ...);
From the android reference:
This (the groupOwnerIntent) is an integer value between 0 and 15 where
0 indicates the least inclination to be a group owner and 15 indicates
the highest inclination to be a group owner.
Furthermore, the demo probably repeatedly sends the file to the same device because there is always made a socket connection to the ip-address obtained from:
WifiP2pInfo.groupOwnerAddress
If you would like to support bidirectional communication, the first step in setting this up would be sending the ip-address of the non group owner to the group owner.
As far as the disconnect/reconnect problem goes, I seem to have the same inconsistencies with Android 4.0.2 devices.

I have been trying for a while to transfer files between two devices using wifi direct. I have use the Android SDK WifiDirectDemo as base. My experience:
GO address is always the same (at least in Samsung Nexus), but this is not really a problem, because you can use this to know who is the server (or client).
Another strange thing was that MAC address of devices were different when you got it from Android WifiManager and when you read it from "/proc/net/arp" file.
At the end I did it, and you can see the code here.
I hope it helps you!

I have been struggling with the same problem lately. I suppose this is an OS issue. To give you a brief background, I have installed Wi-Fi Direct application to both devices with different OS versions, one with OS 4.0.1 and one with OS 4.0.2. The connection fails from time to time when I disconnect and reconnect the devices. It goes same while searching for devices too. But the thing is, this only happens on the device with OS 4.0.2. Other device does not crash or disconnect.
While searching for that problem, I have found the links below. People discussed about that and they share the same idea. Apparently this is an OS 4.0.2 issue. I am not sure if it is the same for OS 4.0.3 but there is no problem with the previous version OS 4.0.1 for sure.
Here are the links:
http://code.google.com/p/android/issues/detail?id=24402
http://osdir.com/ml/android-platform/2012-01/msg00226.html

USB Connection notification

can we receive notification if user connected there phone through USB cable.

Actually there is one broadcast event; if you turned on Debug in your application settings, your will see a bug on your notification bar when you plugged usb. Following is the sample how it works;
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
// UsbManager.ACTION_USB_STATE -> "android.hardware.usb.action.USB_STATE" actually
if (action.equals(UsbManager.ACTION_USB_STATE)) {
Bundle extras = intent.getExtras();
// UsbManager.USB_CONNECTED -> "connected" actually
usbConnected = extras.getBoolean(UsbManager.USB_CONNECTED);
...
You can find this at framework/base/service/java/com/android/server/NotificationManagerService.java.
Hope this helps.

Ajay,
I wasn't able to find anything specific to just "USB Connected," but there are a few Broadcast Actions that may be of interest in this case depending on what you are trying to accomplish:
ACTION_MEDIA_SHARED: External media is unmounted because it is being shared via USB mass storage.
ACTION_UMS_CONNECTED: The device has entered USB Mass Storage mode. This is used mainly for the USB Settings panel.
ACTION_UMS_DISCONNECTED: The device has exited USB Mass Storage mode. This is used mainly for the USB Settings panel.
There doesn't seem to be a Broadcast Action specific to USB simply being plugged in, you could also try doing something with:
ACTION_POWER_CONNECTED: External power has been connected to the device.
But this would go off for both USB connected to a computer and USB connect ONLY to a power source...
Interestingly, I also found this LINK simply stating that there was no Broadcast Action for "USB Connected".
You may be out of luck in this case :-\

Since: API Level 5
An activity to run when device is inserted into a car dock. Used with ACTION_MAIN to launch an activity. For more information, see UiModeManager.
Constant Value: "android.intent.category.CAR_DOCK"
public static final String CATEGORY_CAR_MODE
Since: API Level 8
Used to indicate that the activity can be used in a car environment.
Constant Value: "android.intent.category.CAR_MODE"

A number of years later... this might help someone that came looking like I did. Since Honeycomb, there are two actions one can listen for USB_DEVICE_ATTACHED and USB_DEVICE_DETACHED.