Develop Reference

Android TextView text updation on receiving data from Inputstream

I am coding a client-server app to test communication between two Android Bluetooth devices. On my client, I am reading data from the inputstream object.
When I checked by printing on the logcat, the data is being read successfully. However when I try to set the data to a TextView, it is not displaying.
In the following code, packetsReceivedTV is the TextView object. I am getting correct output when I print 'result' on logcat, but the text is not setting in the TextView. Is it because I am setting the text in a while (listening) loop?
while(listening){
bytesRead =instream.read(buffer);
if(bytesRead!=-1){
String dataRead= new String(buffer,"UTF-8");
System.err.println("*************result : "+dataRead);
packetsReceivedTV.setText("Received : "+dataRead);
packetsReceivedTV.invalidate();
}
}
Even a call to invalidate() is not working.
NOTE: Occasionally when I kill the server process on one device, then the TextView on the client device updates correctly. But this does not happen always. Please help!

It's not clear which thread your code is called on, but you need to make sure these two operations are happening on different threads:
The stream polling needs to be done on a background thread. If you are not doing this, then you are not seeing text because the thread blocking on read() keeps the main thread from updating the UI elements.
The setText() method call must happen on the main (UI) thread. If you are not doing this, the text will also not display--and on some devices you will even see crashes.
I'll assume this code live in an activity (since you are trying to update UI elements). While this is not the best practice, a simple example that demonstrates the concept follows:
Thread pollingThread = new Thread() {
#Override
public void run() {
…
//This code needs to be running on a background thread
while(listening){
bytesRead = instream.read(buffer);
if(bytesRead != -1){
String dataRead= new String(buffer,"UTF-8");
System.err.println("*************result : "+dataRead);
runOnUiThread(new Runnable() {
#Override
public void run() {
//This code needs to be posted back to the main thread.
packetsReceivedTV.setText("Received : "+dataRead);
}
});
}
}
}
};
//Start the listener thread
pollingThread.start();
This is really just meant to illustrate the basic point that the polling code must be in the background and the view code must be on the main thread.
Even a call to invalidate() is not working.
TextView calls this internally when its contents change, so you calling it is redundant.

How to get user feedback (e.g. from AlertDialog) inside AsyncTask/Background-Thread?

an Android 4+ app should perform a long running operation. This could be copying a million files from A to B for example. To not block the UI this operation runs in the background using an AsyncTask.
Assume that the operation needs some user feedback in the middle of the process to continue its work, e.g. "File XY already exists. Override, Irgnore or Rename?"
What is the best way to get this feedback from the user? Since the operation is running in a background thread one could not just present an AlertDialog (or something similar) since UI interaction is only possible in the main thread...
So for I came across these solution:
Ask for feeback before background threads starts, e.g. ask how to handle conflicts before starting to copy/move the files in the
background.
Do not handle conflicts but note them to ask the user
how to handle them after the operation is complete in a new
operation.
End the background operation on the first conflict, ask the user for feedback and continue a new background operation
I do not like any of these solutions. In the first case the user is asked for feedback even if there will be no conflict at all. The second solutions is not possible if the steps have to be processed in a specific order. The third solution would result in code that is very difficult to read/understand/maintain.
A good solution would be:
Stop the background thread
Marshal to the UI thread and get feedback from the user
Resume background thread and use feedback to continue the operation
Using GCD in Objectiv-C/iOS or async/await in C# this is not a big problem. But how can this be done in Android using AsyncTask?

Meanwhile I thought, that I found an answer here: Simply run myActivity.runOnUiThread(...) within doInBackground(...) and wait for it. Sounds good, but it does not work. The AsyncTask/background thread does NOT wait for the Runnable to finish:
private void copyFiles() {
CopyTask copyTask = new CopyTask (this);
copyTask.execute();
}
private class CopyTask extends CustomAsyncTask<Void, Void, Void> {
private doCopy;
#Override
protected Boolean doInBackground(Void... params) {
// Custom code, e.g. copy files from A to B and check for conflict
for (File file : allFiles) {
doCopy = true;
if (isConflict(file)) {
// Stop current thread and ask for user feedback on UI Thread
Runnable uiRunnable = new Runnable() {
public void run() {
// Pos 1. --> Execute custom code, e.g. use AlertDialog to ask user if file should be replaced...
doCopy = false;
synchronized (this) {
this.notify();
}
}
});
synchronized(uiRunnable) {
// Execute code on UI thread
activity.runOnUiThread(uiRunnable);
// Wait until runnable finished
try {
uiRunnable.wait();
}
catch (InterruptedException e ) {
e.printStackTrace();
}
}
}
// Pos 2. --> Continue work
if (doCopy)
copyFromAToB(File);
}
return null;
}
}
I would expect, that when a conflict is detected the Runnable is executed and and Pos 1 (code inside Runnable to resolve conflict) is executed BEVOR Pos 2 is reached. This is not the case. The Runnable is executed correctly but the AsyncTask does not wait for it to finish. The execution of doInBackground is continued without any interruption. It seems that doInBackground and the Runnable are executed in parallel (not suprising since they are executed on different threads) but why does doInBackground not wait?

Android dynamic UI update from AsynchTask/Handler and Thread priorities

I am using an AsynchTask to host a simulator that runs indefinelly and posts the results after each simulation step.
Limiting the simulation loop in background at a maximum of 25Hz, and only calling a javascript function with the results, it works "fine".
Apart from updating a webgl model in a browser, what looks fast enough, I have two more things to update from the Android UI: the FPS indicator and the panel with TextViews representing some of the values. If we forget about the FPS:
The onProgressUpdate() function is already limited to be called at 25Hz, to refresh the model. Now I use another time variable to limit, inside this method, the call to another method that updates the UI panel textViews. It is limited to 1Hz, less than what I actually wanted but fast enough for the kind of information. The method is as clean as possible, all the views are previously loaded to a variable that I keep to not load them every time.
What is the effect: looks like updating 5 textViews takes like one second where all the UI freezes, the touch moves are very very laggy...
I decreased the priority of the background task with:
#Override
protected Boolean doInBackground(ModelSimulation... params) {
Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
...
And used Thread.yield() at the end of the doInBackground method. This improves the behavior to what I explained, without these commands, the behavior is even worst.
My questions are:
-Can I reduce even more the priority if instead of using a background task I use a handler and my own Thread?
-Will a service improve the behavior of the UI?
-Why updating 5 textViews takes so long compared with calling a javascript function that finally will have to use the gpu to change the webgl model?
-Is Android not prepared in any sens to do dynamic applications? How applications like the ones to test sensors update so fast the UI? because there are not standar components like the textViews? (like browser going faster than a textView)
Note: even reducing the refreshing limitations, it produce a laggy effect every time the HUD is updated. In fact I talk about 5 textViews but only updating the FPS indicator produces the same pause. Looks like the only fact of having to switch to the UI thread already consumes this time.
Edit 1:
#Override
protected Boolean doInBackground(ModelSimulation... params) {
Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
if(simulator.getSimulatorStatus().equals(SimulatorStatus.Connected)){
try {
while (true){
//TODO Propagate
long dur = (System.nanoTime()-time_tmp_data);
if(dur<Parameters.Simulator.min_hud_model_refreshing_interval_ns){
try {
long sleep_dur = (Parameters.Simulator.min_hud_model_refreshing_interval_ns-(System.nanoTime()-time_tmp_data))/1000000;
if(sleep_dur>0){
Thread.sleep(sleep_dur);
}
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
time_tmp_data = System.nanoTime();
SpacecraftState sstate = propagate();
int progress = (int)((extrapDate.durationFrom(finalDate)/mission.sim_duration)*100);
if(sstate!=null){
SimResults results = new SimResults(sstate, progress);
simulator.getSimulationResults().updateSimulation(results.spacecraftState, results.sim_progress);
publishProgress();
}
if(isCancelled())
break;
Thread.yield();
}
} catch (OrekitException e) {
// TODO Auto-generated catch block
e.printStackTrace();
simulator.showMessage(simulator.getContext().getString(R.string.sim_orekit_prop_error)+": "+e.getMessage());
}
}
return true;
}
#Override
protected void onProgressUpdate(Void... values) {
//Update model by push
simulator.getSimulationResults().pushSimulationModel();
//Update GUI HUD
if(time_tmp_gui==0 || (System.nanoTime()-time_tmp_gui)>Parameters.Simulator.min_hud_panel_refreshing_interval_ns){
time_tmp_gui = System.nanoTime();
simulator.getSimulationResults().updateHUD();
}
}
If I comment the line simulator.getSimulationResults().updateHUD(); or directly the contents of the method, it works "fine". And this method is only changing some textviews text:
public synchronized void updateHUD(){
//Log.d("Sim",System.currentTimeMillis()+": "+"pre update gui 1");
activity.runOnUiThread( new Runnable() {
#SuppressLint("ResourceAsColor")
public void run() {
if(view != null){
if(panel_time != null)
panel_time.setText(info.time.replace("T", " "));
if(panel_progress != null)
panel_progress.setProgress(info.progress);
if(panel_vel != null){
panel_vel.setText("Vel. "+String.format("%.2f", info.velocity)+" Km/s");
if(info.velocity>config.limit_velocity)
panel_vel.setTextColor(activity.getResources().getColor(R.color.panel_limit));
else
panel_vel.setTextColor(activity.getResources().getColor(R.color.panel_value));
}
if(panel_accel != null){
panel_accel.setText("Accel. "+String.format("%.2f", info.acceleration)+" Km/s2");
if(info.acceleration>config.limit_acceleration)
panel_accel.setTextColor(activity.getResources().getColor(R.color.panel_limit));
else
panel_accel.setTextColor(activity.getResources().getColor(R.color.panel_value));
}
if(panel_radium != null)
panel_radium.setText("Orbit radium: "+String.format("%.1f", info.orbit_radium)+" Km");
if(panel_mass != null)
panel_mass.setText("Mass: "+String.format("%.1f", info.mass)+" Kg");
if(panel_roll != null)
panel_roll.setText("Rol: "+String.format("%.1f", (180*info.roll/Math.PI))+"º");
if(panel_pitch != null)
panel_pitch.setText("Pitch: "+String.format("%.1f", (180*info.pitch/Math.PI))+"º");
if(panel_yaw != null)
panel_yaw.setText("Yaw: "+String.format("%.1f", (180*info.yaw/Math.PI))+"º");
}
}
});
//Log.d("Sim",System.currentTimeMillis()+": "+"post update gui 1");
}
Edit 2: I can actually remove the runOnUiThread since it is already at that thread, but the effect is the same, this is not the problem.
Edit 3: I tried to comment all the lines of the method updateHUD() and leave only these two:
if(panel_time != null)
panel_time.setText(info.time.replace("T", " "));
The effect is almost the same, if I touch any textView, the animation goes by steps like periodically freezing
Edit 4:
I noticed that the process inside the AsyncTask was taking longer than the available step time so it was never sleeping. I established a safe guard time of 10ms that is slept even if the simulation step is longer than the available time. So, I have minimum 10ms free of each 100ms. The efect stills the same. I am updating at 25Hz the browser and 1Hz a single textview text. If I disable the textview update, the webgl model animates smoothly. On the other hand, if I enable the textview update too, every time the text is updated, there are some miliseconds where the browser animation and its response to touches are blocked. This effect gets worst if I increase the task priority. I tried setting a huge guard of 500ms but the freezing effect stills appearing. I am using XWalkView, can it be something blocking the interaction of this view when UI Thread is acting?
I can't understand why a 4 core 2 RAMgb device needs way more time to compute the same simulation than in Linux or windows desktop PC. I have 25Hz-->40ms of available time and the steps take almost 70ms. In a PC I could keep the simulation at 25Hz in real time. Is there so much shit running in background in Android compared to other OS?

There must be another issue with your code. Try posting your AsyncTask in here.
You could also try something very basic like:
Create a new Thread that loops every 25Hz and update your UI by using the post() method of your UI elements or the runInUiThread() of your Activity. See if there's any code still running inside the UI Thread, that could do heavy work, that can be done outside the UI Thread.

I tried literally everything except for the most logic thing, trying the application without the debugger connected.
The reason to have slower simulation than in a PC, to freese UI events... all because the debugger takes a lot of resources from the device. So, I guess that from this point and avobe I will have to test the application without debugger, what forces me to reboot the phone each time to avoid the "waiting for debugger to connect".
Thank to all who tried.

I could be wrong, but I think that yours problem in synchronization on simulator.getSimulationResults() object. I can't see the realization of the simulator class and realization of the object returned by getSimulationResults(), but I suppose that getSimulationResults() returns the same object every time? If so, then it can be looks like this:
In the AsyncTaks call simulator.getSimulationResults().updateSimulation(...). If this method is synchronized, then this call will be lock the SimulationResults object for AsyncTaks thread.
updateSimulation(...) returns, and publishProgress() is called, but publishProgress() is only schedule the onProgressUpdate(Void... values) in the UI thread.
The new iteration in the AsyncTaks thread can be started befor the UI thread gets the control and executes onProgressUpdate(Void... values). So, AsyncTaks thread goes to the first step.
The UI thread gets the control and executes the onProgressUpdate(Void... values) and synchronized void updateHUD() methods, but updateHUD() can't be executed, because SimulationResults object is locked by the AsyncTaks thread in the updateSimulation(...) method. So the UI thread returns the control to the OS. This may occur many times.
So, onProgressUpdate(Void... values) method and all events in the UI thread can be executed only if the UI thread gets the control in the right moment when updateSimulation(...) method is not called in the AsyncTask thread.
You can check this idea by replacing the public synchronized void update HUD() on the public void update HUD(), and write something randomly in the TextView.
In any case, the use of AsyncTask in this case is not the best idea. AsyncTask's are executed in the TheadPool, but in the Android system this pool can consist from only one thread. So, all AsyncTask's will be executed one by one in the one thread.

RunOnUiThread inside loop efficiency

Is it fine to do following if we think about efficiency?
new Runnable() {
#Override
public void run() {
try {
final Runnable uitask = new Runnable() {
public void run() {
//sth that modifies UI
}
};
for (...) {
context.runOnUiThread(uitask);
Thread.sleep(...);
}
} catch (Throwable t) {
}
}
}
I'm most concerned about that runOnUi might create new thread each time, which would be very bad? Am I right or it smarter like ThreadPool?

Well, runOnUiThread doesn't create new threads, it is starting your runnable on the existing UI thread.
but instead of your code you could just do
void onCreate(..) {
...
mHandler = new Handler();
}
for (...) {
mHandler.postDelayed(uitask, DELAY * i++);
}

I'm most concerned about that runOnUi might create new thread each
time, which would be very bad?
Well. It depends what you want to achieve. In Android, native threads are not much efficient. There are more effective ways how to do background work (SDK provides them).
If you want to do some periodical work you can use Handler to achieve your goal. Just create only one Runnable and then you can send request for periodical callbacks. Another solution is to use Services which run in background. They're directly designated for long-running tasks and provide very handy way for background processing.
Sometimes you need to inform user with some information about current progress in your tasks so in this case you can simply use mentioned Handler or AsyncTask.
I think your solution is not clean and efficient. If you'll create for example 40 Threads, your work won't be faster or more efficient at all. Your GB will scream and application will take the greater part of CPU and high battery consumption is something you shouldn't allow.

Android 2.2: How can you write a helper method to have your app 'sleep' for N milliseconds?

I need to write a helper method which I can use in various places in the app to essentially make it 'sleep' for N milliseconds.It looks like Handler.postAtTime may be one way to do it, but I'd like any code snippets if available.

You did not say why you need your app to "sleep".
Assuming you need to run a task after some time:
Handler h = new Handler();
h.postDelayed(new Runnable() {
public void run() {
// do something here
}
}, 1000); // 1000 ms delay

If you don't mind blocking the thread, an alternative to Thread.sleep() is SystemClock.sleep().
Benefit is that it's a one-liner, as it ignores the
InterruptedException so you don't need to handle it.
More info on http://developer.android.com/reference/android/os/SystemClock.html.
As already stated, you should avoid calling this on the main UI thread as it will cause your app to become unresponsive and potentially show the dreaded dialog we all hate to see (please wait or force close.)

Are you looking for something like this?
try {
//Put the thread to sleep for the desired amount of time (milliseconds)
Thread.currentThread().sleep(1000);
}
catch(InterruptedException ie){
}
This will put the thread you are calling it from to sleep for the amount of time you specify.