My USB Host is receiving sensor data and it is getting updated every 200ms. I would like to read this data in my android app every 200ms. I am able to read it using bufferreader, It reads the data for sometime and then hangs. It is not consistent. I am new to this and may be I am not doing it the correct way. Below please find my code and let me know your suggestions. Thanks in advance.
public void startProcessOne()
{
new CountDownTimer(110,100)
{
#Override
public void onTick(long millisUntilFinished)
{
StringBuilder text = new StringBuilder();
line = "";
try {
FileReader in = new FileReader("/mnt/udisk/TEST.TXT");
BufferedReader br = new BufferedReader(in);
int i=0;
char[] buf = new char[10000];
while((i = br.read(buf,i,100))!= -1)
{
String h = new String(buf);
text.append(h);
text.append('\n');
}
br.close();
}
catch (IOException e) {
//You'll need to add proper error handling here
}
TxtRead.setText(text.toString());
}
#Override
public void onFinish()
{
startProcessOne();
}
}.start();
}
TxtRead.setText(text.toString());
This line is causing the problem. You can't touch UI elements from a background thread. You should instead run those codes in the UI/Main thread.
In your case, I'd personally prefer using Java threads. So, create a background thread to keep running periodically. If you would need to run UI methods from that background thread. You probably need a handler attached to the main thread.
// Instantiate a handler in UI thread
final Handler handler = new Handler();
new Thread(new Runnable(){
// Once you're done and want to break the loop, just set this boolean
private boolean stopped = false;
#Override
public void run(){
while(!stopped) {
// Read from the file
// Whenever you need to update an UI element,
// you should wrap it inside this runnable object
handler.post(new Runnable(){
#Override
public void run(){
// Update UI
TxtRead.setText("new_text");
}
})
try {
// This thread will sleep for 9 seconds
Thread.Sleep(9000);
} catch(Exception e){}
}
}
}).start();
Related
I have this problem. I'm trying to update my TextView from another thread and it's not letting me.
I have tried a bunch of different solutions and none of those didn't seem to help. In my while loop code is printing that "Started new loop" all the time but it's not continuing from that runOnUiThread.
Can anyone help me figure out how to update TextView from another thread?
//second thread
protected void startKakkosThread() {
Thread t2 = new Thread() {
public void run() {
while (true) {
System.out.println("Started new loop");
runOnUiThread(new Runnable() {
#Override
public void run() {
try {
if(rullaavaNumero >= 0) {
rullaavaNumero--;
System.out.println(rullaavaNumero);
pelaajanPisteetTeksi.setText("" + rullaavaNumero);
sleep(1000);
}else{
rullaavaNumero = 9;
System.out.println(rullaavaNumero);
pelaajanPisteetTeksi.setText("" + rullaavaNumero);
sleep(1000);
}
}catch (InterruptedException e){
e.printStackTrace();
}
}
});
}
}
};
t2.start();
}
Here is a quick fix, you have an infinite loop that runs faster than a thread can have a chance (time) to start. So even thus you have a sleep in side your thread with if statement, if the thread never starts then sleep have no effect.
And your sleep inside a Thread won't work like this. You want to delay your infinite while loop, therefore you need to move sleep on out of the thread in your while loop.
It is still possible to delay your thread by adding extra sleep in it, but all that depends on what you want to achieve.
Your final code would look like this:
protected void startKakkosThread() {
Thread t2 = new Thread() {
public void run() {
while (true) {
System.out.println("Started new loop");
runOnUiThread(new Runnable() {
#Override
public void run() {
if (rullaavaNumero >= 0) {
rullaavaNumero--;
System.out.println(rullaavaNumero);
pelaajanPisteetTeksi.setText("" + rullaavaNumero);
// no need for sleep here
// sleep(1000);
} else {
rullaavaNumero = 9;
System.out.println(rullaavaNumero);
pelaajanPisteetTeksi.setText("" + rullaavaNumero);
// no need for sleep here
// sleep(1000);
}
}
});
// add this part
try {
sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
};
t2.start();
}
I have test it and it works, you could also go what #cricket has suggest.
My eye saw another issue, which is not a part of your question, but good to mention. I assume you want to count from 9 to 0, if that is the case, you need to correct following line by removing = otherwise you get counts till -1, so your code line would look like this:
if(rullaavaNumero > 0) {...
So I have this method called PredictionEngine(int) that I want to run a certain number of time with a certain time-delay between each run. The method goes like this:
private void PredictionEngine(int delay) throws Exception {
final Handler handler = new Handler();
handler.postDelayed(new Runnable() {
#Override
public void run() {
enableStrictMode();
String val = null;
try {
if (tHighPass == 0 && tLowPass == 0 && tKalman == 1) {
//Magic
} else {
//Magic
}
} catch (Exception e) {
e.printStackTrace();
}
enableStrictMode();
new DropboxTask(side_output, "Result", val).execute();
}
}, delay);
}
As obvious, I am running a network operation in the main thread as this is a research app and no client is ever going to use it.
I want this whole function to run for say a 100 times with a certain delay, say 2 seconds. The initial thought was to do this:
for(loop 100 times){
PredictionEngine(int)
Thread.sleep(2000); //sorry for StackOverflow programming.
}
However I don't want to block the main thread as I am reading some sensor data there. Any ideas for the same would be very helpful!
Thanks.
The best way to solve this is by using rxJava library, because it allow to create, modify and consume streams of events. You can implement everything in a few lines of code and modify it so operatioin will be performed in background as well.
Observable.interval(1, TimeUnit.SECONDS)
.take(100)
// switch execution into main thread
.subscribeOn(AndroidSchedulers.mainThread())
.subscribe(t -> {
doSomethingOnMainThread();
});
On the other hand, there is another solution- you can use Handler, which is usually bein used for thread communication. It has method .postDelayed() allowing you to postpone execution of task. Handler can be conveniently used along with HandlerThread. But, rxJava is more convenient and simple way to solve your problem.
While creating your Handler, you can provide a looper as one of the constructors parameters that is based on different thread then the main thread:
HandlerThread thread = new HandlerThread("Thread name", android.os.Process.THREAD_PRIORITY_BACKGROUND);
thread.start();
Looper looper = thread.getLooper();
Handler handler = new MyHandler(looper);
Messages received by MyHandler will be processed on a separated thread, leaving the UI thread clear from interferences.
To loop on the task periodically, use something like:
for (int i=0; i<100; i++){
handler.postDelayed(new Runnable(){
...
...
...
}, i*delay);
}
This way, in case you decide that the periodic tasks need to be canceled, you will always be able to invoke:
handler.removeCallbacksAndMessages(null);
I tried to solve the issue as follows without blocking the main Thread
I created the worker thread for looping and still running the predictionEngine() on main thread
MyThread t = new MyThread(2000, 3000); // delay and sleep
t.startExecution();
Worker thread class looks as follows
class MyThread extends Thread{
private int delay;
long sleep;
MyThread(int delay, long sleep){
this.delay = delay;
this.sleep = sleep;
}
#Override
public void run() {
for(int i = 0; i < 100; i++){
try {
MainActivity.this.runOnUiThread(new Runnable() {
#Override
public void run() {
predictEngine(delay);
}
});
Log.i("Mtali","About to pause loop before next predict");
sleep(sleep);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
void startExecution(){
start();
}
}
Hop this helps!
I am new to Android, but I ran into this problem...
I need an infinite loop to run some process in the background,
while another infinite loop to accept some socket connection,
and then when a button clicked, I need to make a socket connection to some server.
Almost all the example and tutorial I can find are showing how to create one single thread.
I have try to use runnable (this seems to run at foreground?)
Runnable r=new Runnable() {
public void run() {
while(true){}
}
}; r.run();
and I have tried to use AsyncTask (this run at background, but only one AsyncTask per activity?)
private class Run extends AsyncTask<Void, Void, Void> {
protected Void doInBackground(Void... params) {
}
}
but whatever I do, my program only execute the first thread.
My question would be, is it possible to have multi-thread running multi-infinite loop within one activity? If is, how?
Yes, you can create multiple threads.
You can implement the Runnable interface.
new Thread(new Runnable() {
public void run() {
while (true) {
//code something u want to do & it will run infinitely.
//Remove the infinite loop for running finite set of operations.
Log.i("Thread", "Running parallely");
}
}
}).start();
Also, please note that the above thread run indefinitely. If you want to do any finite operations, just put the code inside the run method.
To create a thread that listen for network Connection
new Thread(new Runnable() {
public void run()
{
ServerSocket s = new ServerSocket(PORT_NUMBER);
while(true)
{
Socket c = s.accept();
// read the socket
BufferedReader in = new BufferedReader(new InputStreamReader(c.getInputStream()));
in.read();
}
c.close(); //close the socket
}
}).strat();
Sometimes you want to call up the UI thread from the background thread. You can do that like this:
Thread t = new Thread(new Runnable() {
public void run() {
//Do your background thing here
getActivity().runOnUiThread(new Runnable() {
public void run() {
//Update your GUI here
}
});
t.start();
And getActivity looks like this:
public class YourClass extends AppCompatActivity{
private Activity getActivity(){
return this;
}
//Rest of class here
}
I have an app that runs 2 threads in loops. 1st one is updating a graph in 1s interval and the second one is updating another graph at 60s interval. The second task is taking a long time since it is quering some server in the internet 3 times that might not always be available and even if it is it will take up to 5-7s to execute.
What is happening is when I launch the second thread it will pause execution of the first one and that is not what I want, I wish both run concurrently. Here in the Youtube video you can see the results of the app running. http://youtu.be/l7K5zSWzlxI
"thread_updater1s" is running a green graph, large readout, and a timer in the corner so you clearly see it stalls for 11 seconds.
1)First of all why is that happening? how to fix it?
2)I'm aware that I might not launch the threads properly at all. I had hard time understanding how to make something to run in a interval loop in Java and my code worked fine for one graph/tread. Now when I have 2 loops in separate threads I don't know why they are not executing concurrently.
Here is the code:
public class LoopExampleActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.main);
thread_updater1s.start();
thread_updater2.start();
}// end of onCreate
final Runnable r1s = new Runnable() {
public void run() {
do_1s_updates(); // those are very quick http calls to the local API server
} // to get data nessessary for some plot.
// They have 1s timeout as well but rarely timeout
};
final Runnable r2 = new Runnable() {
public void run() {
do_large_updates(); //This makes 7 long call over the Internet to the slow https
//server once every 60s. Has 10s timeout and sometimes takes as much as
//7s to execute
}
};
Thread thread_updater1s = new Thread() {
#Override
public void run() {
try {
while (true) {
handler.post(r1s);
sleep(1000);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
Thread thread_updater2 = new Thread() {
#Override
public void run() {
try {
while (true) {
handler2.post(r2);
sleep(60000);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
}
PS. please be forgiving and informative I only code Java for 15 days so far with absolutely no prior experince or lesson.
You need to make the http requests in the threads (not the posted runnables). Then, when you have the data downloaded, you create a runnable with that data that will update the graph and post that runnable to be executed by the UI thread. Here is an example:
public class LoopExampleActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.main);
thread_updater1s.start();
thread_updater2.start();
}// end of onCreate
Thread thread_updater1s = new Thread() {
#Override
public void run() {
try {
while (true) {
final Object data = getDataFromServer1();
handler.post(new Runnable() {
#Override
public void run() {
updateGraph1(data);
}
);
sleep(1000);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
Thread thread_updater2 = new Thread() {
#Override
public void run() {
try {
while (true) {
final Object data = getDataFromServer2();
handler.post(new Runnable() {
#Override
public void run() {
updateGraph2(data);
}
);
sleep(60000);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
Obviously, change that final Object data by the appropriate class that represents your data downloaded.
handler.post pushes the runnable onto the main (UI) thread's message queue for execution on the main thread.
So what you're doing is every sleep interval, you're sending a message to the main thread to run the function. Clearly, the main thread can't run 2 things at once, so that's why one runnable is delayed for the next one.
You probably want to do the work of the runnable in the separate threads - why did you start using a handler? What happens if you call do_1s_updates and do_large_updates directly instead of through the handler & runnable?
ive been thinking about this for hours and im not closer to an solution!
My thread just stops looping when im fetching a message from an server for some reason, and works perfectly when im not doing it.
This works and prints refreshing every second:
public class ChatRoom extends Activity implements OnClickListener, Runnable {
private Thread t = new Thread(this);
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.chatroom);
Button send = (Button) findViewById(R.id.send);
send.setOnClickListener(this);
Intent receiver = getIntent();
String host = receiver.getStringExtra("Host");
int port = receiver.getIntExtra("Port", 4456);
try
{
socket = new Socket(host, port);
this.receive = new BufferedReader(new InputStreamReader(this.socket.getInputStream()));
this.send = new PrintWriter(this.socket.getOutputStream(), true);
}
catch(IOException ioe) { System.out.println(ioe); }
t.start();
}
public void run()
{
String message = "";
while(true)
{
try
{
// message = receive.readLine(); BufferedReader
t.sleep(1000);
}
//catch(IOException ioe) { System.out.println(ioe); }
catch (NullPointerException npe) { System.out.println(npe); }
catch (InterruptedException e) { System.out.println(e); }
System.out.println("Refreshing...");
}
}
And when i use my commented code, it actually works and i get a message from the server but it loops just once! Why is that?
Output:
Server Message
Refreshing...
I get no Exception or errors, but i had an error before with some similar code that said that i cant change UI on other threads. So ive been looking at some runOnUiThread but it didnt make it better, and i dont know why it should :(
The method BufferedReader.readLine() blocks until a newline character is received. If there is no newline in your receiver stream it will block forever.
A few things here:
Swap from System.out.println("string"); to Log.d("tagname","string"); then look on DDMS for output lines.
I don't think you're creating a thread properly, and you certainly aren't providing any interface to kill it, which may cause issues when you test it. I would separate the thread into a new file, say NameOfThread:
//File "NameOfThread"
public class NameOfThread extends Thread{
//any fields you want here to mess with e.g.
private String message;
private boolean running;
public NameOfThread(){
message = "";
running = true;
}
#Override
public void run(){
while(running){
//do stuff
}
}
public void setRunning(boolean run){
running = run;
}
}
//When you want to call it
NameOfThread varThread = new NameOfThread();
varThread.start();
//when you want to kill the thread
varThread.setRunning(false);
You may think 'why bother with this whole running variable junk, I don't need it.' but how else will this thread end gracefully? There is another method of killing the thread properly, which is using InterruptedException and your cleanup code goes there, but that's just an alternative.
Try doing this first, then you'll need to sort out the message itself (the method you're using currently isn't great since readLine() will block until a line is received (meaning you'll get "Refreshing..." when you get a new line rather than once per second.
You're surely getting some exceptions thrown, you just can't see them cause you're trying to print them on the standard output, which is missing on Android. Your exception is handled correctly and the code finishes. To properly get the exception information use Logs, or just throw a RuntimeException. Hope this helps.