We Keep Coding

How UI element "textview" can be operated by background thread "t"

public class MainActivity extends AppCompatActivity {
private TextView textView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = findViewById(R.id.textview);
Thread t=new Thread(new Runnable() {
#Override
public void run()
{
textView.setText("Hello");
}
});
t.start();
}
}
I was expecting wrong thread exception. And what is meaning of "scheduleTraversals in mThread=[main,5,main] currentThread=[thread-2,5,main]", how it is different from "CalledFromWrongThreadException".

You can't. Sub thread cannot modify the ui. There is a way to do this:
Thread t=new Thread(new Runnable() {
#Override
public void run()
{
runOnUiThread(() -> {
textView.setText("Hello");
});
}
});
t.start();

Android / java - Using a timer Loop inside an onClick

This is my first question so I apologise if the format isn't correct.
I'm using java and trying to get a timer to run within a while loop when a button is clicked. The result should cause a .setText to alter the text in a box periodically once the start button is clicked.
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
startBtn = findViewById(R.id.startButton);
item = findViewById(R.id.Rule);
startBtn.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
while(true)
{
Timer();
}
}
});
}
public void Timer()
{
Handler handler = new Handler();
handler.postDelayed(new Runnable()
{
#Override
public void run()
{
item.setText()
}
}, 5000);
}`
The issue is that when the start button is hit, nothing seems to happen.
Alternatively I also tried repeating the timer call instead. Whilst this worked it will only run the timer call once and then end the click function.
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
startBtn = findViewById(R.id.startButton);
item = findViewById(R.id.Rule);
startBtn.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
Timer();
Timer();
Timer();
Timer();
Timer();
}
});
}
public void Timer()
{
Handler handler = new Handler();
handler.postDelayed(new Runnable() {
#Override
public void run() {
item.setText(ruleOut(rulesList));
}
}, 5000);
}
I haven't been able to find anything or work anything out for this so any help is much appreciated. I'm sure that i'll be missing something obvious. Thank you.

what you are doing is you are running all the timers at the same time so all are getting executed at the same time try to run this code
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
startBtn = findViewById(R.id.startButton);
item = findViewById(R.id.Rule);
startBtn.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
for(int i = 5000; true; i= i+5000){
Timer(i);
}
}
});
}
public void Timer(int time)
{
Handler handler = new Handler();
handler.postDelayed(new Runnable()
{
#Override
public void run()
{
item.setText(String.valueOf(time));
}
}, time);
}`

Problem:
Your Timer method:
public void Timer() {
Handler handler = new Handler();
handler.postDelayed(new Runnable() {
#Override
public void run() {
item.setText(ruleOut(rulesList));
}
}, 5000);
}
What it does is create a new handler and posts(schedules) a block of code to run after 5 secs and returns immediately without actually executing that code.
So when you call this method multiple times, it schedules the task and returns immediately and schedules the task again and so on. Since the functions returns immediately, all the scheduled Runnable's are executed at the same time.
When you call this method inside an infinite loop, it schedules and returns and schedules and return and so on forever and never returns, causing the freezing of app.
Solution:
To solve your method you can modify the run() method to call this method after the scheduled task has been executed.
public void Timer() {
Handler handler = new Handler();
handler.postDelayed(new Runnable() {
#Override
public void run() {
item.setText(ruleOut(rulesList));
Timer();
}
}, 5000);
}
And set your click handler as:
startBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Timer();
}
});
In this way, as soon as you click the button, the setting of text will be scheduled to be done after 5 secs and the method Timer will run and schedule the task again.

CountdownTimer crashing app. Trying to update UI thread on tick

I want the countdowntimer to be on a separate thread and for it to update the UI on each tick. Every time I click start the app just closes and I get the 'app has stopped' error message.
public class Activity_MultiplayerGame extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity__multiplayer_game);
}
public void btnStart_onClick(View view){
CountDownTimer timer = new CountDownTimer(15000, 1000){
#Override
public void onTick(final long millisUntilFinished) {
runOnUiThread(new Runnable() {
#Override
public void run() {
TextView countdownText = (TextView) findViewById(R.id.countdown);
Integer timeUntilFinished = (int) millisUntilFinished/1000;
countdownText.setText(timeUntilFinished);
}
});
}
#Override
public void onFinish() {
TextView countdownText = (TextView) findViewById(R.id.countdown);
countdownText.setText("Finished");
}
};
timer.start();
}
}
I've made the assumption that creating a CountDownTimer gives it its own thread?

you can use Handler. I wrote a sample for you
this code increase a counter every one second and show and update counter value on a textView.
public class MainActivity extends Activity {
private Handler handler = new Handler();
private TextView textView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = (TextView) findViewById(R.id.text);
startTimer();
}
int i = 0;
Runnable runnable = new Runnable() {
#Override
public void run() {
i++;
textView.setText("counter:" + i);
startTimer();
}
};
public void startTimer() {
handler.postDelayed(runnable, 1000);
}
public void cancelTimer() {
handler.removeCallbacks(runnable);
}
#Override
protected void onStop() {
super.onStop();
cancelTimer();
}
}

You cannot update UI from other thread than main (ui) thread on android. There are many ways to approach the problem, but I suppose you should start with AsyncTask if you really need another thread. Check doInBackround and onProgressUpdate methods.
If you don't need other thread (and if this is only about the counter you dont') you can check Handler class and postAtTime(Runnable, long), postDelayed(Runnable, long) methods. Or you can make subclass of Handler class and use combination of sendMessageDelayed(android.os.Message, long) and overridden handleMessage().

Here's your problem:
countdownText.setText(timeUntilFinished);
You have passed integer to setText(int) method, which actually takes the string resource id rather than the integer to be displayed. You should use the method setText(String).
Try this:
countdownText.setText(String.valueOf(timeUntilFinished));

This code also work it decrease counter(or increase whatever you want) and show in text view you can also stop or reset counter via click the same button.
public class MainActivity extends AppCompatActivity {
TextView textView;
Button count;
boolean timelapseRunning = true;
int NUM_OF_COUNT=15;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView=(TextView)findViewById(R.id.textview);
count=(Button)findViewById(R.id.count);
runTimer();
}
public void onclick(View view){
if (!timelapseRunning) {
timelapseRunning=true;
} else {
timelapseRunning = false;
}
if(NUM_OF_COUNT==0){
NUM_OF_COUNT=15;
}
}
private void runTimer() {
final Handler handler = new Handler();
handler.post(new Runnable() {
#Override
public void run() {
textView.setText(""+NUM_OF_COUNT);
if (!timelapseRunning && NUM_OF_COUNT>0) {
NUM_OF_COUNT--;
}
handler.postDelayed(this, 1000);
}
});
}
}

The CountDownTimer gives out callbacks on the same thread, in which it was created. So the runOnUiThread in onTick is absolutely not required if the CountDownTimer constructor was called on UI thread.
Also,
TextView countdownText = (TextView) findViewById(R.id.countdown);
being called in onTick method is poor design, as findViewById method consumes considerable processing power.
Finally the actual problem as Nabin Bhandari pointed out is the integer value passed to setText method. You need to wrap it to string.
This code is enough
final TextView countdownText = (TextView) findViewById(R.id.countdown);
CountDownTimer timer = new CountDownTimer(15000, 1000) {
#Override
public void onTick(long millisUntilFinished) {
countdownText.setText(String.valueOf(millisUntilFinished/1000));
}
#Override
public void onFinish() {
countdownText.setText("Finished");
}
};
timer.start();

I/Choreographer(12759): Skipped 40 frames! The application may be doing too much work on its main thread

I'm new to android programming and I recently searched for simple fade-out animation for an object. I've put it in my code, tested it and it was choppy. I checked the logs and saw this :
11-05 19:19:21.319: I/Choreographer(12759): Skipped 40 frames! The application may be doing too much work on its main thread.
Here's my code in the MainActivity class
private MainActivity actMain;
FadeIn fadeClass = new FadeIn();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViewById(R.id.view_switcher);
actMain = this;
new Thread() {
#Override
public void run() {
// If there are stories, add them to the table
try {
// code runs in a thread
runOnUiThread(new Runnable() {
#Override
public void run() {
fadeClass.animation(actMain);
}
});
} catch (final Exception ex) {
Log.i("---", "Exception in thread");
}
}
}.start();
}
And from the FadeIn class:
private View view;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void animation(Activity context) {
final View view = context.findViewById(R.id.fadeOutLayer);
Animation fadeOut = new AlphaAnimation(1f, 0f);
fadeOut.setDuration(3000);
fadeOut.setAnimationListener(new AnimationListener() {
#Override
public void onAnimationStart(Animation animation) {
}
#Override
public void onAnimationRepeat(Animation animation) {
}
#Override
public void onAnimationEnd(Animation animation) {
view.setVisibility(View.GONE);
}
});
view.startAnimation(fadeOut);
}
Thank you!

You are creating and executing a new thread in the main thread, and inside of this new thread, you are executing a runOnUiThread, that synchronize with the Main thread and executes its content in it. It makes no sense, because is like execute the content of runOnUiThread in the onCreate.
I recommend that you use the "fadeClass.animation(actMain);" directly inside of onActivityCreated

You can also animate by simply using animate() method for simple animations. Animations like alpha, rotation, scale are available. I am giving an example of translation.
mImageView.animate().translationX(-screenWidth)
.setDuration(ANIMATION_DURATION).withEndAction(new Runnable() {
#Override
public void run() {
mImageView.setImageDrawable(d);
mImageView.setVisibility(View.INVISIBLE);
}
});
Can be done easily on main thread

Where does handler really post its messages to?

I'd like to know the limits and how Handlers work in Android.
I can understand why this works exactly as expected:
public class MainActivity extends Activity {
TextView tv;
Handler mHandler;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mHandler = new Handler();
tv = new TextView(this);
tv.setText("original text");
setContentView(tv);
new Thread(new Runnable() {
#Override
public void run() {
mHandler.post(new Runnable() {
#Override
public void run() {
tv.setText("changing from instance member handler");
}
});
}
}).start();
}
that code, as expected, changes the TextView without complaining for being on wrong thread. i made my handler on UI thread.
however, what i don't understand is... why does THIS also work?
public class MainActivity extends Activity {
TextView tv;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
tv = new TextView(this);
tv.setText("original text");
setContentView(tv);
new Thread(new Runnable() {
Handler handler = new Handler();
#Override
public void run() {
handler.post(new Runnable() {
#Override
public void run() {
tv.setText("changing from different thread.");
}
});
}
}).start();
}
Two questions:
1) I've made my handler from a non-UI thread, but it still updates the textview without complaining about touching a view outside of UI thread. why is that? Where are my messages actually being posted to?
2) say i have 20 pieces of code like that, where i make a new Handler instance each time, will there ever be a problem with running off of UI thread, or a performance issue?
Note: if i made a thread inside of a thread, and instantiate the handler in that inner inner thread, THEN the TextView can't be touched there.

Only code inside run() is executed in another thread. All the initialization is done in the thread that creates the class. And the Runnable is created entirely inside the ui thread.
If you were to write it like
new Thread(new Runnable() {
#Override
public void run() {
Handler handler = new Handler();
handler.post(new Runnable() {
#Override
public void run() {
tv.setText("changing from different thread.");
}
});
}
}).start();
You would get a crash because there is no looper in the thread.