Develop Reference

Is there a way to detect internet connectivity change when phone is connected to wifi over hotspot?

Phone A has mobile data ON and is sharing internet via Wi-Fi hotspot to Phone B. If Mobile Data is TURNED OFF in phone A, no connectivity change is received #PhoneB. How can I get this change in Phone B when mobile data is turned ON/OFF in Phone A?
Phone B is Android phone.

Yes there is. Simply register BroadcastReceiver for connectivity changes:
#Override
public void register(Context context) {
receiver = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
if (isOnline()) {
if (listener != null) {
listener.onConnected();
}
hideNoConnectionError();
} else {
showNoConnectionError();
}
}
};
final IntentFilter intentFilter = new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
context.registerReceiver(receiver, intentFilter);
}
and on change event check whatever connectivity change there was

How to know if my BluetoothDevice is connected?

I'm trying to check if my BluetoothDevice is connected to something.
If it is connected, obtain the data of the other device
I want to implement this function to my application since I need to monitor if the connection was lost or is still connected and add a visual indicator in case the connection changes.
Tried with this function but the toast shows nearby devices (not connected) constantly:
if (BluetoothDevice.ACTION_ACL_CONNECTED.equals(action)) {
BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
String name = device.getName();
Toast.makeText(getApplicationContext(),name,Toast.LENGTH_SHORT).show();
}

AFAIK there is no way to view the state of the connection. Instead you monitor for changes in the state of the bluetooth connection. So you can register a receiver and then receive a broadcast when the device is disconnected.
IntentFilter filter = new IntentFilter();
filter.addAction(BluetoothDevice.ACTION_ACL_DISCONNECTED);
this.registerReceiver(rec, filter);
private BroadcastReceiver rec = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if (BluetoothDevice.ACTION_DISCONNECTED.equals(action)) {
// Bluetooth is now disconnected
}
}

How to check if a bluetooth device is paired

I'm trying to check if there is a bluetooth device paired when running my app.
In the main activity, I find bluetooth devices and pair to them. In the second activity, I must check if there is a device paired or not.
If a device is conected, it starts automatically sending data, but if there is no conexion, then it simply shows a toast.
I need to do this just when the second activity starts. I found this code, but I don't know how to make it to start when the activity is just created.
public void onCreate() {
//...
IntentFilter filter1 = new IntentFilter(BluetoothDevice.ACTION_ACL_CONNECTED);
IntentFilter filter2 = new IntentFilter(BluetoothDevice.ACTION_ACL_DISCONNECTED);
this.registerReceiver(mReceiver, filter1);
this.registerReceiver(mReceiver, filter2);
}
//The BroadcastReceiver that listens for bluetooth broadcasts
private final BroadcastReceiver BTReceiver = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if (BluetoothDevice.ACTION_ACL_CONNECTED.equals(action)) {
//Do something if connected
}
else if (BluetoothDevice.ACTION_ACL_DISCONNECTED.equals(action)) {
//Do something if disconnected
}
}
};

Here is a complete description of the problem, with the correct answer to solve it:
Action to know if there is any bluetooth paired device

How to detect if bluetooth device is connected

In android how can my Activity will get to know if a Bluetooth A2DP device is connected to my device.
Is there any broadcast receiver for that?
How to write this broadcast receiver?

Starting from API 11 (Android 3.0) you can use BluetoothAdapter to discover devices connected to a specific bluetooth profile. I used the code below to discover a device by its name:
BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
BluetoothProfile.ServiceListener mProfileListener = new BluetoothProfile.ServiceListener() {
public void onServiceConnected(int profile, BluetoothProfile proxy) {
if (profile == BluetoothProfile.A2DP) {
boolean deviceConnected = false;
BluetoothA2dp btA2dp = (BluetoothA2dp) proxy;
List<BluetoothDevice> a2dpConnectedDevices = btA2dp.getConnectedDevices();
if (a2dpConnectedDevices.size() != 0) {
for (BluetoothDevice device : a2dpConnectedDevices) {
if (device.getName().contains("DEVICE_NAME")) {
deviceConnected = true;
}
}
}
if (!deviceConnected) {
Toast.makeText(getActivity(), "DEVICE NOT CONNECTED", Toast.LENGTH_SHORT).show();
}
mBluetoothAdapter.closeProfileProxy(BluetoothProfile.A2DP, btA2dp);
}
}
public void onServiceDisconnected(int profile) {
// TODO
}
};
mBluetoothAdapter.getProfileProxy(context, mProfileListener, BluetoothProfile.A2DP);
You can do that for every bluetooth profile. Take a look at Working with profiles in Android's guide.
However, as written in other answers, you can register a BroadcastReceiver to listen to connection events (like when you're working on android < 3.0).

You cannot get the list of connected devices by calling any API.
You need instead to listen to the intents ACTION_ACL_CONNECTED, ACTION_ACL_DISCONNECTED that notifies about devices being connected or disconnected.
No way to get the initial list of connected devices.
I had this problem in my app and the way I handle it (didn't find better...) is to bounce off/on the Bluetooth at application start to be sure to start with an empty list of connected devices, and then listen to the above intents.

muslidrikk's answer is broadly correct; however you can alternatively use fetchUUIDsWithSDP() and see what you get back... it's a bit of a hack though -- you'd have to know what UUIDs (capabilities) you could expect from the device, if it were turned on. And that might be difficult to guarantee.

For BluetoothHeadset specifically, you can call getConnectedDevices() to get connected devices for this specific profile.
Reference: http://developer.android.com/reference/android/bluetooth/BluetoothHeadset.html
Other cases you need to register a receiver for that.

In your activity, define broadcast receiver...
// Create a BroadcastReceiver for ACTION_FOUND
private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
// When discovery finds a device
if (BluetoothDevice.ACTION_FOUND.equals(action)) {
// Get the BluetoothDevice object from the Intent
BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
// Add the name and address to an array adapter to show in a ListView
mArrayAdapter.add(device.getName() + "\n" + device.getAddress());
}
}
};
// Register the BroadcastReceiver
IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
registerReceiver(mReceiver, filter); // Don't forget to unregister during onDestroy

How can I monitor the network connection status in Android?

I have a Service that is downloading a file from a server. I warn the user to only download the file over Wireless LAN before the download starts.
My problem is that my download gets stuck if I loose the network connection. Is there a way to listen for changes in network connection or if it is lost entirely?

Listen for CONNECTIVITY_ACTION
This looks like good sample code. Here is a snippet:
BroadcastReceiver networkStateReceiver = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
Log.w("Network Listener", "Network Type Changed");
}
};
IntentFilter filter = new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
registerReceiver(networkStateReceiver, filter);