Develop Reference

Websocket paused when android app goes to background

My android app starts a service that opens a websocket to communicate to a remote server. The service spawns a thread whose run method looks like this.
public void run() {
try {
super.run();
for(int i = 1; i < 1000; i++) {
Log.d(TAG, String.format(" *** Iteration #%d.", i));
Thread.sleep(3000); // Dummy load.
mWebsocket.sendTextMessage("Test");
}
}
catch (Exception exc) {
Log.d(MY_TAG, "MyThread.run - Exception: " + exc.getMessage());
}
}
When I turn off the screen or send the app to the background, logcat shows that the loop is running, but the remote server stops receiving the test messages. Apparently, the messages are pooling somewhere because once the app is back to the foreground, the server will received a bunch of test messages. Is this the expected behavior on Android? I've tried different Websocket packages (Autobahn, okhttp3, ...) and the result is the same.

If you want this function to be guaranteed to continue to run while your app's UI is in the background, you will need to make that service run as a foreground service. There are some restrictions/guidelines on the use of foreground services, see the documentation at https://developer.android.com/guide/components/services.html.
Alternatively, if this is work that needs to occur on a periodic recurring basis and does not need to run continuously, you may be able to utilize JobScheduler; see https://developer.android.com/topic/performance/scheduling.html.

Android Toast prevents my devices to sleep

I use Toast to indicate my app's state. And I use the following code in order to control toast showing time.
Toast noCardDetectedToast=null;
void setVisibilityNoCardDetectedToast(boolean visible)
{
if(visible)
{
if(noCardDetectedToast==null)
noCardDetectedToast = Toast.makeText(this, R.string.msg_no_card_detected, Toast.LENGTH_SHORT);
noCardDetectedToast.show();
}
else
{
if(noCardDetectedToast!=null)
{
noCardDetectedToast.cancel();
noCardDetectedToast=null;
}
}
}
When it's necessary to show this Toast, the application starts invoking setVisibilityNoCardDetectedToast(true) several times per second.
And when the application doesn't need this toast any more, it invokes setVisibilityNoCardDetectedToast(false).
Everything works fine, but my android device does not fall asleep, as long as the toast is visible.(I tested my application on Android 4.x and 5.0)
This behaviour looks strange for me. What do I do wrong here?

Android, holding tcp connection in sleep mode

I am trying to keep a tcp connection to a server alive even while the phone goes into sleep mode. I have searched everywhere and tried everything. This problem occurs on some phones and not others which is kind of random.
So basically one client sends a request to the server, then the server sends the request to another client. What happens is that the receiving client doesn't get the request at all. I have tested this with a debugger and the next line of code after the read never gets called. It is important for the device to receive the message right away. I am wondering how viber is achieving this. I thought about google cloud messaging but i would have to re-implement a lot, also according to the documentation, even with google cloud messaging the message doesn't necessarily reach the destination right away.
here is my code:
class BackgroundReadThread extends Thread {
#Override
public void run()
{
while(connectedToServer)
{
try
{
int bytesRead=0;
if(myWifiLock!=null && !myWifiLock.isHeld())
myWifiLock.acquire();
byte val=(byte)myInputStream.read();
myWakeLock.acquire();//this line never gets called when in sleep
if(val==-1)
{
unexpectedDisconnectionFromServer();
if(myWifiLock!=null && myWifiLock.isHeld())
myWifiLock.release();
myWakeLock.release();
return;
}
bytesRead=myInputStream.read(myBuffer, 0, bufferSize);
if(bytesRead<1)
{
unexpectedDisconnectionFromServer();
if(myWifiLock!=null && myWifiLock.isHeld())
myWifiLock.release();
myWakeLock.release();
return;
}
byte[] dataArray=Arrays.copyOfRange(myBuffer,0,bytesRead);
ByteBuffer data=ByteBuffer.allocate(bytesRead+1).put(val).put(dataArray);
myParent.invokeReceiveAction(data, bytesRead+1);
}
catch (IOException e)
{
myWakeLock.acquire();
unexpectedDisconnectionFromServer();
e.printStackTrace();
}
finally
{
if(myWifiLock!=null && myWifiLock.isHeld())
myWifiLock.release();
if(myWakeLock!=null && myWakeLock.isHeld())
myWakeLock.release();
}
}
}
}
EDIT: forgot to mention that this code is running in a service

I have no idea why but the problem only occurs sometimes and it only occurs on the debug version of the application. I have tested the release version of the application and it never failed once on any of the phones ive tested it on. So i guess the problem is with the debug version although i have no idea why. Hope this helps someone having similar problems.

Sending alert from bluegiga dongle to android handset

I am trying to develop a BLE bluetooth (SMART) application for Android.I am using the Broadcom-ble API
I have a requirement to send alerts from Bluegiga dongle to the android handset. I send alert values such as 0,1,2 from bluegiga. Whenever I send the alert, the following callback is invoked inside my application:
#Override
public void onCharacteristicWrite(String address, BleCharacteristic charObj) {
Log.d(TAG, "onCharacteristicWrite(" + address + ", " + charObj + ")");
}
The following line of code gives nullpointer, when I try to fetch the alert value from the charObj
byte alertLevel = charObj.getValue()[0];
I have checked and confirmed, charObj is not null. But charObj.getValue() returns null.
Can someone please let me know, though the callback is invoked correctly when I send an alert from bluegiga, why I am unable to retrieve the sent value, from my application?
Any help is appreciated.

How to auto-accept Wi-Fi Direct connection requests in Android

I have 2 Android devices using WiFi Direct. On one device I can get information about the other device using the WifiP2pManager class, and request a connection to the other device. However when I request a connection, the other device pops up a little window and asks the user if they want to accept the connection request.
Is it possible to auto-accept these connection requests? I.E to be able to connect to the other device without user confirmation?

It can be easily done with the help of Xposed framework. You just need to replace the single method inside one of android java classes (see the link from snihalani's answer). But of course to use Xposed your device must be rooted. The main idea can be expressed in the following code (using Xposed)
#Override
public void handleLoadPackage(LoadPackageParam lpparam) {
try {
Class<?> wifiP2pService = Class.forName("android.net.wifi.p2p.WifiP2pService", false, lpparam.classLoader);
for (Class<?> c : wifiP2pService.getDeclaredClasses()) {
//XposedBridge.log("inner class " + c.getSimpleName());
if ("P2pStateMachine".equals(c.getSimpleName())) {
XposedBridge.log("Class " + c.getName() + " found");
Method notifyInvitationReceived = c.getDeclaredMethod("notifyInvitationReceived");
final Method sendMessage = c.getMethod("sendMessage", int.class);
XposedBridge.hookMethod(notifyInvitationReceived, new XC_MethodReplacement() {
#Override
protected Object replaceHookedMethod(MethodHookParam param) throws Throwable {
final int PEER_CONNECTION_USER_ACCEPT = 0x00023000 + 2;
sendMessage.invoke(param.thisObject, PEER_CONNECTION_USER_ACCEPT);
return null;
}
});
break;
}
}
} catch (Throwable t) {
XposedBridge.log(t);
}
}
I tested it on SGS4 stock 4.2.2 ROM and it worked.
I guess the same could be done with the help of Substrate for android.

From my current understanding of the API, You cannot really accept connections automatically without user's intervention. You can initiate a connection, that doesn't require user intervention. If both of your devices are mobile devices, you will have to accept connection request on one end.
I have put this as a feature request in android project hosting.
You can monitor their response here: https://code.google.com/p/android/issues/detail?id=30880

Based on the comments, do you really need to connect to the devices if you just want to track and log the vehicles around you ?
I don't know the scope of the project, but you could simply use the WifiP2pDeviceList that you get when you request the peers in the WifiP2pManager. You could get the list of the devices (~= vehicles) around you and could log this.
Connection is useful if you want to send more detailed information I guess.

If you can modify the framework, you can ignore the accept window and direct send the "PEER_CONNECTION_USER_ACCEPT".
Base on Android 5.0, "frameworks/opt/net/wifi/service/java/com/android/server/wifi/p2p/WifiP2pServiceImpl.java".
You must find the "notifyInvitationReceived", and modify to ...
private void notifyInvitationReceived() {
/*Direct sends the accept message.*/
sendMessage(PEER_CONNECTION_USER_ACCEPT);
/*
... old code
*/
}