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Pausing with handler and postDelayed in android

I'm very new to android programming so please forgive my noobie-ness. I'm trying to create a very simple activity that will have one TextView in the middle of the Layout and just have it switch to a different text every couple of seconds. For example, the TextView will say "text1", pause for a couple of seconds, then say "text2, and pause again. Eventually, I want to add more texts and have them all cycle one after another. I know this seems like a super simple thing but I'm mainly trying to learn about threads and handlers at this moment. Anyways, I've read up on how we should keep lengthy things off the UI thread to prevent an error so I thought I'd use a handler to simply switch between 2 texts on screen. Unfortunately, I can't get this to work. Here's some code:
public class MainActivity extends Activity {
String[] myarray = {"text1" , "text2"};
int arraylength = myarray.length;
int count;
Handler handler = new Handler();
TextView mytexts;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mytexts = (TextView)findViewById(R.id.my_texts);
mytexts.setText(myarray[0]);
Thread t = new Thread( new Runnable(){
public void run() {
for (int count = 0; count < arraylength; count++){
handler.postDelayed(new Runnable(){
public void run() {
mytexts.setText(myarray[1]);
}
}, 7000);
}
}
});
t.start();
}
}
From what I can see in the logcat, the handler seems to run postDelayed one right after another (in my code's case, it does NOT wait 7 seconds with the postDelay to do another postDelayed). Also, I would like to make the 1 in "mytexts.setText(myarray[1]);" be the same as "count" in the for loop so it can be the same as one of the strings in the array but that gives me an error. I've been stuck on this for hours and other examples I've found online seem way too complicated for someone like me who mainly wants to get the basics down before I can tackle other things. Any help at all with any of this would be much appreciated. Thank you.

postDelayed is non blocking, meaning it would add it to a queue of I'll do this later. So what you are probably seeing is all text updates happening together at the 7th second. I say this because you are postDelaying from the onCreate method when in reality you probably want to do it from onResume or even onPostResume.
Also there is no reason to create a thread to add runnables to the post queue. Your code should look more like this:
(Note the time to delay multiplier)
#Override
protected void onResume() {
super.onResume();
for (int count = 0; count < arraylength; count++){
handler.postDelayed(new Runnable(){
#Override
public void run() {
mytexts.setText(myarray[count]);
}
}, 7000 * (count + 1));
}
}

This is because your loop is setting all your handlers to run after 7 seconds not 7 seconds after each other but but after 7 seconds from now. You can either add in the postDelayed method or use the postAtTime method in handler .
Also, you don't need to do this in a thread, you can get rid of that altogether.

Populating listview in separate thread

In an activity I load rows of a listview which takes much time, therefore I put this task in a separate thread to allow displaying a progressDialog.
I do the following
private void doMyStuff() {
listItems.clear();
progressDialog.show();
new Thread(new Runnable() {
#Override
public void run() {
for () {
listItems.add(something to add);
}
handler.sendEmptyMessage(0);
progressDialog.dismiss();
}
}).start();
}
private Handler handler = new Handler() {
public void handleMessage(android.os.Message msg) {
if (msg.what == 0) {
adapter.notifyDataSetChanged();
}
};
};
I have sometimes a bug which raises an IllegalStateException. First of all I was surprised, because programming thread like that is what I usually do in standard Java programs.
The bug appears only "sometimes" and it does not appear when doing step by step debugging.
This lead me to search around the web and I found some questions in SO related to this and I must admit that things are not clear to my mind.
As I call the notifyDataSetChanged() only when the thread finished why does it sometimes raises an exception.
Can someone confirm me that this way of doing is wrong, and that I MUST use async task and perhaps explain me why ???
I need to have a progressDialog displayed, can someone give me a simple example of AsyncTask populating a listview AND displaying a progressDialog of the populating progress.
Thanks
UPDATE
jtanveer gave me the answer to the asynctask question. Now the others pointed out that the dismiss is not in the handler, which I correct.
According to the article given by jtanveer on "Painless Threading" they say that
Android offers several ways to access the UI thread from other threads which one of them is HANDLER.
Does someone know why putting the dismissed in the handler did not solve my problem ? for me listItem.add has nothing to do with UI ? Am I wrong on that point ?
For me, in my code the only UI is adapter and progressdialog ? Any commentary or explanation is welcome.
FINAL ANSWER
stjom gave a working answer for my specific code. Running the runOnUiThread in the handler. It's working but I am surprised because I thought the handler was run in the Ui Thread ...
Thanx to all for all your answers.

define an inner class like below:
private class LoadListTask extends AsyncTask<String, Void, Integer> {
protected void onPreExecute() {
progressDialog.show();
}
protected Integer doInBackground(String... params) {
for () {
listItems.add(something to add);
}
return 0;
}
protected void onPostExecute(Integer result) {
progressDialog.dismiss();
if (result == 0) {
adapter.notifyDataSetChanged();
}
}
}
if you need, you can refer to this article.

whenever you call adapter.notifyDataSetChanged(); it identifies any changes to your listItems object. if any change is found, it will update the UI accordingly which I think causes your problem. you can call
runOnUiThread(new Runnable() {
public void run() {
adapter.notifyDataSetChanged();
}
});
inside your handler.

You don't need to use AsyncTask, its just a convenience.
As far as why your current implementation doesn't work sometimes -
You should dismiss your progress dialog from the UI thread, so that needs to go in your handler, not your background thread.

Implementing a while loop in android

I can't understand the implementation of a while loop in android.
Whenever I implement a while loop inside the onCreate() bundle, (code shown below)
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
setContentView(R.layout.main);
TextView=(TextView)findViewById(R.id.TextView);
while (testByte == 0)
updateAuto();
}
nothing boots up, and the program enters a "hanging" state after a while and I can't understand why. Testbyte is as follows:
byte testByte == 0;
and updateAuto() is supposed to update the code per 1 second and display inside the textView portion. I've been using setText inside updateAuto() as shown below and everything works fine, but once i implement the while loop all i see is a black screen and then an option to force close after a few seconds due to it "not responding".
TextView.setText(updateWords);
I've changed it to a button format (meaning i have to click on the button to update itself for now), but i want it to update itself instead of manually clicking it.
Am i implementing the while loop in a wrong way?
I've also tried calling the while loop in a seperate function but it still gives me the black screen of nothingness.
I've been reading something about a Handler service... what does it do? Can the Handler service update my TextView in a safer or memory efficient way?
Many thanks if anyone would give some pointers on what i should do on this.

Brace yourself. And try to follow closely, this will be invaluable as a dev.
While loops really should only be implemented in a separate Thread. A separate thread is like a second process running in your app. The reason why it force closed is because you ran the loop in the UI thread, making the UI unable to do anything except for going through that loop. You have to place that loop into the second Thread so the UI Thread can be free to run. When threading, you can't update the GUI unless you are in the UI Thread. Here is how it would be done in this case.
First, you create a Runnable, which will contain the code that loops in it's run method. In that Runnable, you will have to make a second Runnable that posts to the UI thread. For example:
TextView myTextView = (TextView) findViewById(R.id.myTextView); //grab your tv
Runnable myRunnable = new Runnable() {
#Override
public void run() {
while (testByte == 0) {
Thread.sleep(1000); // Waits for 1 second (1000 milliseconds)
String updateWords = updateAuto(); // make updateAuto() return a string
myTextView.post(new Runnable() {
#Override
public void run() {
myTextView.setText(updateWords);
});
}
}
};
Next just create your thread using the Runnable and start it.
Thread myThread = new Thread(myRunnable);
myThread.start();
You should now see your app looping with no force closes.

You can create a new Thread for a while loop.
This code will create a new thread to wait for a boolean value to change its state.
private volatile boolean isClickable = false;
new Thread() {
#Override
public void run() {
super.run();
while (!isClickable) {
// boolean is still false, thread is still running
}
// do your stuff here after the loop is finished
}
}.start();

Task not finishing and forbidding TextView to be updated

I am now working on an android app in which I need to display a text after some processing is done.
I'm using a Thread to run a process in the back while my progress dialog is being displayed to the user. The Thread works properly and I've followed it step by step and, apparently, it also ends fine; however, the method in which I call it does not seem to come to an end (at least, during a normal cycle) because the text I am setting afterward does display immediately, I have to wait and do some other action (like in order for it to display
Below is the piece of code I'm having trouble with:
private OnClickListener saldoDisp = new OnClickListener(){
public void onClick(View v){
int x = s2.getSelectedItemPosition();
branchSel = arrSucsId[x];
mainProc();
saldoAdminTex.setText(strSaldo); //The late one
}
};
public void mainProc(){
chekP = new Thread (null,doProc,"Background");
chekP.start();
mProgress =ProgressDialog.show(SivetaAsaldo.this, "","Obteniendo saldo...",true, false);
}
private Runnable doProc = new Runnable(){
public void run(){
if(getSaldoAdmin(levelSel,branchSel))
{
mProgress.dismis();
Log.i(TAG,"Task completed properly");
}else
handler.post(tosti);
}
};
So I do get the "Task completed properly" but seems like it still waits for something else, any clues guys?
Thanks for taking a bit of your time to check it out =).

saldoAdminTex.setText(strSaldo); //The late one
is going to get called immediately. It doesn't wait until after the Thread started in mainProc ends. You also cannot dismiss the Progress Dialog in your runnable. You can only do UI related things on the main UI thread.
It would help you to read the article on Painless Threading on the Android Dev site.

About your ProgressDialog, please see this answer about how to use a AsyncTask with a ProgressDialog.

Looking at your code, this:
saldoAdminTex.setText(strSaldo);
would potentially be executed before your thread finishes as the thread will be running in parallel to that line.
An alternative way would be to do this:
public void mainProc(){
mProgress =ProgressDialog.show(SivetaAsaldo.this, "","Obteniendo saldo...",true,false);
handler.post(new Runable(){
public void run(){
if(getSaldoAdmin(levelSel,branchSel))
{
mProgress.dismis();
saldoAdminTex.setText(strSaldo);
Log.i(TAG,"Task completed properly");
}else
handler.post(tosti);
}
});
}

MultiThreading issues while programing for android

I am developing on Android but the question might be just as valid on any other Java platform.
I have developed a multi-threaded app. Lets say I have a first class that needs to do a time-intensive task, thus this work is done in another Thread.
When it's done that same Thread will return the time-intensive task result to another (3rd) class.
This last class will do something and return it's result to the first-starting class.
I have noticed though that the first class will be waiting the whole time, maybe because this is some kind of loop ?
Also I'd like the Thread-class to stop itself, as in when it has passed it's result to the third class it should simply stop. The third class has to do it's work without being "encapsulated" in the second class (the Thread one).
Anyone knows how to accomplish this ?
right now the experience is that the first one seems to be waiting (hanging) till the second and the third one are done :(

If you want to use threads rather than an AsyncTask you could do something like this:
private static final int STEP_ONE_COMPLETE = 0;
private static final int STEP_TWO_COMPLETE = 1;
...
private doBackgroundUpdate1(){
Thread backgroundThread = new Thread() {
#Override
public void run() {
// do first step
// finished first step
Message msg = Message.obtain();
msg.what = STEP_ONE_COMPLETE;
handler.sendMessage(msg);
}
}
backgroundThread.start();
}
private doBackgroundUpdate2(){
Thread backgroundThread = new Thread() {
#Override
public void run() {
// do second step
// finished second step
Message msg = Message.obtain();
msg.what = STEP_TWO_COMPLETE;
handler.sendMessage(msg);
}
}
backgroundThread.start();
}
private Handler handler = new Handler(){
#Override
public void handleMessage(Message msg) {
switch(msg.what){
case STEP_ONE_COMPLETE:
doBackgroundUpdate2();
break;
case STEP_TWO_COMPLETE:
// do final steps;
break;
}
}
}
You would kick it off by calling doBackgroundUpdate1(), when this is complete it sends a message to the handler which kicks off doBackgroundUpdate2() etc.

Tiger ,
TiGer wrote:
When it's done that same Thread will
return the time-intensive task result
to another (3rd) class
Since thread runs asynchronously so your non-thread class can't be synced with your thread
Though to perform some action on an Activity you need an AsyncTask not A Thread
TiGer wrote:
maybe because this is some kind of
loop ?
Tiger do read more about Threads and concurrency
So the only answer I have for you now is ASYNCTASK
EDIT:
Also I'd like the Thread-class to stop
itself
Read this post's how-do-you-kill-a-thread-in-java

In ordinary Java, you would do this:
class MyTask implements Runnable {
void run() {
for (int i = 0; i < Integer.MAX; i++) {
if (i = Integer.MAX -1) {
System.out.println("done");
}
}
}
}
class MyMain {
public static void main(String[] argv) {
for (int i = 0; i < 10; i++) {
Thread t = new Thread(new MyTask());
t.start();
}
System.out.println("bye");
}
}
... that kicks off 10 threads. Notice that if you accidentally invoke t.run() instead of t.start(), your runnable executes in the main thread. Probably you'll see 'bye' printed before 10 'done'. Notice that the threads 'stop' when the the run() method of the Runnable you gave to them finishes.
I hope that helps you get your head around what it is you've got to co-ordinate.
The tricky part with concurrency is getting threads to communicate with each other or share access to objects.
I believe Android provides some mechanism for this in the form of the Handler which is described in the developer guide under designing for responsiveness.
An excellent book on the subject of concurrency in Java is Java Concurency in Practice.

if you want use AsyncTask rather then thread in android
I have resolve it using ASyncTask and Handler in Android the aim is that one task is execute after compilation of one task hear is code that show First load animation on view after compilation of that process it will goes on another page
class gotoparent extends AsyncTask<String,String,String>
{
#Override
protected String doInBackground(String... params) {
runOnUiThread(new Runnable() {
#Override
public void run() {
Animation animation= AnimationUtils.loadAnimation(getApplicationContext(),R.anim.rotete);
lin2.startAnimation(animation);
}
});
return null;
}
#Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
Intent i=new Intent(getApplicationContext(),ParentsCornor.class);
startActivity(i);
}
}, 1200);
}
}