I'm using Handler and HandlerThread to perform asynchronous loading in my application, but something is going wrong, for example:
handler.postDelayed(new Runnable() {
#Override
public void run() {
.....................
}
}, 100);
this handler wrip (sic) in a new HandlerThread and is created in onCreate().
It seems like that is no problem, however there are times when an error appears, one example of this is a NullPointerException caused on this handler - it is stable before - but when I test on 2.1 version emulator this happen some times and I can't solve it, is thee any one that can help me?
have you considered race conditions in your code? it sounds like the handler code is not performing proper synchonization - and might sometimes see changes from a different thread - which again causes your nullPointer exception.
try wrapping your problem code in a synchonized block - or if you are using primitve types only - move to volatile or atomic types.
Related
I know Android UI is not really meant for executing functions and waiting for them to finish, however, I think there are use cases were it is required, like networking.
My problem is, I want to run a series of network operations that rely on each other and take a bit more time than the split second it takes to the next execution, so some waiting is in order:
Start hotspot
Get network interfaces and IP
Start socket
Initially I tested that all is working using buttons, then it waited between my button presses. But now I'd like to automatize it. I googled but all I found are solutions with Async task, which is deprecated. I tried with threads and join, but that usually causes weird crashes in the runnable, and it is not very elegant. I wonder if there is another solution?
The best thing you can do with SDK it's use Executors to run your work in background sequentially
val newSingleThreadExecutor = Executors.newSingleThreadExecutor()
newSingleThreadExecutor.execute {
// 1...
}
newSingleThreadExecutor.execute {
// 2...
}
But if you want to touch the UI from background should create handler check if view's not null
val handler = Handler(Looper.myLooper()!!)
newSingleThreadExecutor.execute {
handler.post {
view?.visibility = View.GONE
}
}
How about something like this?
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
startHotspot();
getNetworkInterfaceAndIP();
startSocket();
}
}, 300);
This is my first Android application and I am finding troubles with while loop, I am trying to use a while loop on my Android application but the application freezes.
What I'm trying to do is track the user location (using onlocationChanged) and keep querying on the location until the query returns a result. It's a GIS application so I am going to describe the application behavior:
the application keeps tracking the user position using a listener "onLocationChangedListener" and store it in a variable "myPosition". I am using a boolean"noResults=true". I will use a method "query(myPosition)" in the while loop, this method has a callback that when a result is found, and changes a boolean "noResults" to false. the loop will keep on until "noResults" is false (that means query's callback changed the boolean's value)
, here's what I did:
while(noResults)
{
//myPosition keeps changing
query(myPosition);
//query has a callback that when a result is found it changes noResults to false
}
I resolved the problem using a "Handler" that query the Feature Layer every 5 seconds, this stops the main thread from generating application not responding error:
Handler m_handler=new Handler();
Runnable m_runnable;
m_runnable = new Runnable(){
public void run() {
//query code here
m_handler.postDelayed(m_runnable, 5000);
}
};
m_handler.postDelayed(m_runnable, 0);
running while loop codes on the main thread freezes the UI, and makes all other processes pause making your app unresponsive use
Threads..
also note that the while loop you are running is running on a default Thread termed as the ui thread so in short run while loops on separate threads..
eg..
new Thread(new Runnable() {
#Override
public void run() {
// Your hard while loop here
//get whatever you want and update your ui with ui communication methods.
}
).start();
for ui communicating methods
View.post(new Runnable() {
#Override
public void run() {
// TODO Auto-generated method stub
Toast.makeText(getActivity(), "updated ui", Toast.LENGTH_LONG).show();
}
});
the view could be any views you are updating..
also like #TehCoder said you could use asynctask but asynctask is not meant for long workaflow work there are 3 of them but i can't recall the last one
Maybe you should use an AsyncTask? I'm not quite sure what your problem is tho.
Loop is not a problem in android (or any language).
There are two scenario might be reason for your freezing,
If you run network call in api, android throw error and crashes. You have to do network related calls in Aysnc Task ot threading
Use try throw catch and exception cases to avoid app crashing and better coding skill.
I am developing on a library that is somehow getting a CalledFromWrongThread Exception crash on Samsung Galaxy S1 (api v7 - android 2.1). The code is something like this:
class MyWebViewClient extends WebViewClient {
#Override
public void shouldOverrideUrlLoading(WebView view, String url) {
someListener.addToUiView();
}
}
and of course, the method that is actually throwing the error (which implements a listener callback):
View v;
public void addToUiView(){
v.addView(new TextView(context)); //<-- this line is throwing the error on rare occasions
}
I'm skipping some code in between, but i'm not doing anything weird in other places. Also note: this crash only seems to have been happening a very very small % of the time. (not necessarily conclusive, as not everyone reports their data).
has anyone else come across this?? Is WebCore threading messing things up?
Now I haven't actually tested this but I am going to answer to the best of my knowledge. That said, my instinct is telling me that you are only seeing the error intermittently because web requests from a WebView (browser) happen with varying levels of asynchronicity and probably utilize a thread pool to accomplish this. Basically, sometimes it requests resources in parallel and sometimes it doesn't. Worse yet you might be seeing this error on only a single device because OEMs optimize OS level code (like the WebView internals) based on their preferences and opinions (especially Samsung). Either way the real problem is that you are doing something "UI related" in a place that is definitely not guaranteed to be "UI friendly"... That is, anywhere where you are getting a subsystem callback.
The solution to your problem is much more simpler than the explanation: just use your context (that I am assuming is an Activity)..
Activitys have a built in function called runOnUiThread(Runnable) that will guard the code inside the runnable from running on the wrong thread. Basically, your problem is really common and android has a built-in solution. runOnUiThread will only add overhead if required, in other words if your thread is the UI thread, it will just run the Runnable, if it isn't it uses the correct Handler (the one associated with the UI thread) to run the Runnable.
Here is what it should look like:
View v;
public void addToUiView() {
final Activity activity = (Activity) context;
activity.runOnUiThread(new Runnable() {
#Override
public void run() {
v.addView(new TextView(activity));
}
});
}
i coded that up right inside the SO window so my apologies for any egregious errors, I hope that helps, and let me know if you need more info or of this doesn't solve your problem -ck
I have been tracing down a problem where a block of my code just stops working. At long last, I identified the line, as seen below:
Log.v(TAG,"Here");
tv.setText("");
Log.v(TAG,"There");
During the time that blocks, the first statement gets called, the second one doesn't. Any idea what could be causing this?
In case there's any doubt, tv is a TextView. There is no errors printed out, and in fact, this line worked once previously...
I figured out what my problem was, I'm posting the answer here to help anyone out in the future. It might be an Android bug, or something odd... No error was ever posted. Bottom line is, don't make GUI calls in a ScheduledThreadPoolExecutor.
ScheduledThreadPoolExecutor masterExecutor;
masterExecutor=new ScheduledThreadPoolExecutor(1);
masterExecutor.schedule(new Runnable(){
#Override
public void run() {
//Formerly, I ran the block of code here, that blocked.
runOnUiThread ( new Runnable()
{
#Override
public void run() {
//Now I moved the code inside of a runOnUiThread
}
});
}
},1000,TimeUnit.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.