Post message from UI thread to worker thread - android

I need to implement reading from a file, line by line. On each line, in case a certain condition is met, a Dialog window appears. The Dialog should have callbacks with returned result. Based on that result, the reading should continue with next line or break execution. I decided to achieve that with a separate worker thread for the reading, using the HandlerThread class, that communicates with the main thread, either with runOnUiThread() to open Dialog, or some Handler implementation. However, it is not very clear to me how to send the result back, from the UI to worker, and with blocking the worker until the result is received so it may continue with the next line. Any suggestions are appreciated. Thanks

Related

Is there a callBack to SetContentView in Android?

Is there any callBack to setContentView in Android, since i'm doing a heavy operation right after setContentView line, and it seems to skip that setContentView.
So i was thinking of moving the heavyOperation to the callBack of setContentView.
Thanks
EDIT:
Pseudo Code:
AudioRecord Finishes
SetContentView(1) //To show a "Processing" screen with no buttons
FFT analysis
SetContentView(2) //On FFT analysis DONE.
In my case "SetContentView(1)" NEVER occurs.
EDIT # 2:
I did the heavy operation in another Thread, and used Handler to send a Message after heavy operation finishes to treat it as a callBack.
Thanks for all the help guys
Short answer: No callback for the setContentView.
If you are doing network operation then you can use the AsyncTask for this.
If you are doing any more heavy operation and want to update the UI then you can do that using the Service and BroadCastReceiver.
For this you have to make your own callback using the interface.
heavy work should be done in asynk tasks or as a service or on other threads
Don't do any heavy calculations on the main UI thread where onCreate() and such are run.
What happens that the first setContentView() posts a "layout and draw" message to the UI thread message queue. Then your calculation blocks the UI thread, preventing messages in the queue from being processed. The second setContentView() posts another message to the queue. When the control eventually returns to the message loop, both messages are processed and you'll get the layout set up by the last call to setContentView().
For heavy computations, use a separate thread. For example, an IntentService or an AsyncTask make threading easier.
My hack.
final Handler handler = new Handler();
setContentView(layoutResID); // This posts some messages to message queue.
handler.post(new Runnable() { // Post another message at the end.
#Override
public void run()
{
// Called after layout has changed.
// If you want to skip some more works (like transitions),
// call another handler.post() here.
}
});
To see what happens, set a break point at the line Message msg = queue.next(); in Looper.loop() may help.
I was facing a quite similar problem a day ago, but I figured it out. (I know your problem is solved, just offering a different approach which doesn't require a handler or callback.
Most Suitable for running U.I. functions :
If you need to do something like this :runTask() then
setContentView() (or any other ui function) you can run the task on different thread by using AsyncTask or you can set a timer for when the task is completed (if your task takes a certain time), the User Interface functions will be called.
But since the Timer class, runs the functions on a different thread, you can not run the setContentView() inside it. So you can use a runOnUiThread(Runnable action) method inside the overloaded run() function of Timer class. You just need to define a function that returns a runnable. Define your Ui operations in the runnable action.
Hope it helps someone.

android async task usage in depending sequence of tasks

My App contains a function that takes time to load ( parsing files).
THe function is called at multiple user case, i.e. from multiple user triggered condition.
Besides, it is called when onCreate is called.
In simple word, the flow is:
User click/OnCreate trigger
Function to parse file
Post to windows
Other postprocessing
I hope the user can click cancel to stop parsing files.
I tried to use asynctask. I know I can put the function to onPostExecute.
But I assume onPostExecute is just for dismiss progress dialog. Or I have to move a lot of codes ( for different cases) to it. Not a good idea.
I do not suppose user to do anything during parsing files.
So, what is the best way to do so? Despite I know it is not good, I think i have to occupy the UI thread.
In simple word, I want to wait for "parsing files", but i do not want to occupy the UI thread, so user can click cancel.
update:
I tried. however, there is a problem:
I use asynctask. I called:
mTask = new YourAsyncTask().execute();
YourAsyncTask.get(); // this force to wait for YourAsyncTask to return.
DoSomethingBaseOnAsyncTaskResult();
YourAsyncTask.get() hold the UI thread. So, there is not loading dialog, and user cannot click cancel from the dialog. It seems I have to move every line after
mTask = new YourAsyncTask().execute();
to
OnPostExecute()
which i did not prefer to do so because DoSomethingBaseOnAsyncTaskResult() can be very different based on the return result. or else, it becomes do everything in YourAsyncTask()
AsyncTasks should ideally be used for short operations (a few seconds at the most.)
When an asynchronous task is executed, the task goes through 4 steps:
onPreExecute(), invoked on the UI thread before the task is executed. This step is normally used to setup the task, for instance by showing a progress bar in the user interface.
doInBackground(Params...), invoked on the background thread immediately after onPreExecute() finishes executing. This step is used to perform background computation that can take a long time.This step can also use publishProgress(Progress...) to publish one or more units of progress. These values are published on the UI thread, in the onProgressUpdate(Progress...) step.
onProgressUpdate(Progress...), invoked on the UI thread after a call to publishProgress(Progress...). The timing of the execution is undefined. This method is used to display any form of progress in the user interface while the background computation is still executing. For instance, it can be used to animate a progress bar or show logs in a text field.
onPostExecute(Result), invoked on the UI thread after the background computation finishes. The result of the background computation is passed to this step as a parameter.
CODING
To start an Async task
mTask = new YourAsyncTask().execute();
and to cancel that task
mTask.cancel(true);
More detail is available here
In order to use the AsyncTask API, one has to follow the steps described below:
Create a class which extends AsyncTask.
Fill in the generic types available as generics in the class for:
the task execution array parameters
progress array parameters
result array parameters
Implement the method doInBackground(Parameters... parameters). This
method must execute the job which is supposed to be quite demanding.
Optionally, one can implement methods for:
cancelling the task - onCancelled(...)
executing tasks before the demanding task - onPreExecute(...)
reporting progress - onProgressUpdate(...)
executing activities after the demanding task is finished
-onPostExecute(...).

Android: Dialog between long run operations

I need a suggestion to implement the following situation:
Showing a dialog between two long run operation (SQLite DB and Network operation) that need to be performed not in UI Thread.
Which dialog is shown depends on the result of first long run operation, whereas which second long run operation is performed depends on the option selected by the user in the dialog. I have used two AsynTask (like below) to make this but program flow is very messy.
Any suggestions to make this more easily?
UI thread calls AsynTask AT1
AT1 doInBackGround() performs long runnung operation 1
AT2 onPostExecute shows dialog
UI thread handles dialog's result (using callback methods) and call AsynTask AT2
AT2 doInBackGround() performs long runnung operation 2
AT2 onPostExecute changes the UI.
You can run each of the tasks in a separate service with its own AsyncTask and have them send their results to a Handler on the UI thread.
The handler should include the logic of deciding what to do with the input.
The communication should go through the bundle via message or a new Parcellable of your creation.
If these operation are long you should consider the user will dismiss the dialog and notify him globally [from Application or notification bar]

Android: Blocking RPC with progress dialog

I have an Android App that uses an RPC mechanism to set/get information to/from a server. I call the RPCs from whithin the main thread (blocking) and I want them to be blocking. However, sometimes a call can last for some seconds and I'd like to display an indeterminate progress dialog after some specified time (e.g. 1 second).
I tried to spawn a new thread that makes the call and the main thread waits in a loop (with sleeps) until the call has been finished. Inside this loope I show the progress dialog but this is not working.
Is it possible to show and update the progress dialog inside another Thread or does anybody know a better solution that allows me to use blocking calls?
You cannot do both, make the main thread wait in a loop and show a progress dialog, at the same time. Either the main thread waits or shows the dialog.
Why do you want to block the main thread? Communication over the internet should always be done in a background thread because you never know how long it will take to complete. Do that stuff in AsyncTask and show the progress dialog in main.
Try using AsyncTask. It is an android mechanism which is used to make such network calls. Get the brief detailing of AsyncTask here:
Using AsynTask to show progress bar while attempting to SSH to Server
Using a AsyncTask you can block the user from proceeding ahead. You have to show a progress dialog in the onPreExecute() method of the AsyncTask. All your network related activities will take place in doInBackground(). After the background action is completed there will be a call to onPostExecute() where the progress dialog will be dismissed.
AsyncTask is a asynchronous call because you have 2 threads working simultaneously, one is the UI thread on which you are showing your progress dialog and the other is the non-ui background thread which is fetching your data from the server.
Hope this explanation helps.
I have found a solution that seems to work (at least I havent noticed any problems yet). I know the proper way would be to use somethn like AsyncTask but in my case I have no benefit from it and it complicates the program logic.
To update the UI within a new thread:
new Thread()
{
public void run()
{
Looper.prepare();
... do UI stuff here
Looper.loop();
}
}.start();

Execution Time of Activity Callbacks

This may have been hidden somewhere in the docs, but I don't remember seeing it:
Assuming everything is running on the same thread, would an activity callback, or any kind of callback for that matter, interrupt a runnable , or even some other callback, executing on the thread, or are they posted sequentially by time of occurance as messages similar to runnables?
It certainly doesn't interrupt execution, at least in the UI thread. For instance, say that you have a Button, and you place a Thread.sleep(10000) in its onClick callback. Well, as soon as you press the button the entire UI will freeze. This wouldn't happen if the onClick callback interrupted the UI thread's execution.
If you wanted to know all the answer of the question you need to use
http://developer.android.com/guide/developing/debugging/debugging-tracing.html
Depends on the Runnable.
All activity callbacks happen in the UI Thread. For example thread for onCreate is same as the thread which calls onTabSelected.
If you are started an AsyncTask, it runs in its own thread.
Try using following Log statement to check your scenario
Log.i("","Thread Id : "+Thread.currentThread().getId());

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