Develop Reference

How to use Async task to pause program multiple times

I know the title is somewhat confusing, my problem is this: I want to "pause" my program multiple times (via a loop) using sleep(ms) and make changes to several buttons that the user has pressed. I understand that changes to the UI can only be made in the main thread, so I am wondering how to convert this code into an Async task. I also remember reading somewhere that Async task can only be called once? If this is so, what other solutions could I look into?
View.OnClickListener SimulateButtonHandler = new View.OnClickListener() {
#Override
public void onClick(View v) {
for(int j=0;j<169;j++) //169 buttons to click
{
if(ClickedPoints[j]!=null) //how I keep track of which buttons has clicked
{ //clear button color
Drawable d2 = ClickedPoints[j].getBackground();
ClickedPoints[j].invalidateDrawable(d2);
d2.clearColorFilter();
}
}
Timer timer = new Timer();
for(int i=0;i<169;i++)
{
if(ClickedPoints[i]!=null)
{ //change the color after some time
Simulate(timer, i);
//clear color again
Drawable d2 = ClickedPoints[i].getBackground();
ClickedPoints[i].invalidateDrawable(d2);
d2.clearColorFilter();
}
}
}
};
public void Simulate(Timer timer, final int index)
{
timer.schedule(new TimerTask()
{
public void run() {
Sim(index);
}
}, 1000); //delay for some amount of time, then rehighlight the button
}
private void Sim(int i)
{
Drawable d1 = ClickedPoints[i].getBackground();
PorterDuffColorFilter filter = new PorterDuffColorFilter(Color.RED, PorterDuff.Mode.SRC_ATOP);
d1.setColorFilter(filter);
}

You'd be better off using a Thread to run your background work (and pausing) and a Handler to access the UI thread.
Here's a good tutorial on using handlers with threads.

Android Async, Handler or Timer?

Every 5 seconds, I want to call my webservice and get text (not images), then display it in my ImageAdapter. What would be the best way to accomplish this?

final Handler handler = new Handler();
final Runnable r = new Runnable()
{
public void run()
{
callWebservice();
}
};
handler.postDelayed(r, 5000);

It depends if you want to use a different thread or not. Do you want the user to be able to interact with the application on the UI Thread while the images are downloading? If so, then I would definitely use an AsyncTask with a small ProgressBar (style="#android:style/Widget.ProgressBar.Small")
If you don't care about threading then what #inazaruk said.
Edit: the truth is most modern apps that retrieve data from a web service will use an AsyncTask with a discreet little loader in the corner just to let the user know it's updating.
Edit 2: here's an example of using a TimerTask to run something every 5 seconds. The key is the runOnUiThread(). There may be better ways to tie all the elements together but this accurately portrays all the pieces.
myTimer = new Timer();
myTimer.schedule(new TimerTask() {
#Override
public void run() {
CallWebService();
}
}, 0, 1000);
}
private void CallWebService()
{
this.runOnUiThread(fetchData);
}
private Runnable fetchData = new Runnable() {
public void run() {
asyncTask.execute();
}
};

You should call asynctask inside the application main thread. Asynctask can't be called in a background thread.

How to set an image with a delay

I have an "Activity" with three images. When one image is clicked, all the images are to switch to another picture. Is there a way to make the switches such that there is a 2 second delay before the images actually change (i.e. a 2 second delay in every 'for loop' below)? I am trying to do this with a timer but it does not actually to the delay when I run my program:
protected void onCreate(Bundle savedInstanceState) {
image1.setOnClickListener(this);
#Override
public void onClick(View arg0)
{
do_switches();
}
private void do_switches()
{
//loop through all images and change them
for(int j=1 ;j<=3; j++)
{
final int curr2=current;
final Handler handler = new Handler();
Timer t = new Timer();
t.schedule(new TimerTask() {
public void run() {
handler.post(new Runnable() {
public void run() {
switch(curr2){
case 1:
image1.setImageResource(ImageArray[1]);
break;
case 2:
image2.setImageResource(ImageArray[2]);
break;
case 3:
image3.setImageResource(ImageArray[3]);
break;
}
}
});
}
}, 2000);
}
}
I have also tried using just SystemClock.sleep(2000) instead of the timer but I that didnt work either.I also tried setting up a Thread with a try/catch with no luck or maybe I didn't implement it properly. Is there a way to put this delay on every iteration of my for loop?
Thanks

Not one of best option, but still you can try CountDownTimer.
http://developer.android.com/reference/android/os/CountDownTimer.html

You can use handler.postDelayed(Runnable r, long timeInMillis). Make your runnable that changes the pictures and then call postDelayed() and pass in the runnable and 2000 for the time delay.
Edit: Ahh I see what you are trying to do. As far as I know you aren't going to be able to make a for loop pause for 2 seconds each time through. You can get the same effect though if you chain the postDelayed() calls. Just set up the next runnable and call postDelayed() on it inside the first one, and same for the third one from inside the second one. You will end up with the same functionality as a for loop that pauses for 2 seconds each iteration.

Android OnDraw()

I am new to Android and I am having trouble understanding the concept so basically this is what i want to do to understand it better..
I created a DrawShape class that extends view. In this class in the OnDraw() I am creating a circle and filling it with a color.
From the Activity I am calling the application. //Until this point I am doing fine.
Now, I need to re-paint the Circle multiple times (Blue, Red, Yellow etc..)
So I was reading and the best way is to use Threads.. I also read you need to use postInvalidate() to redraw (I still dont understand from where I should be calling this) is this called from the Activity?, or within the OnDraw()?.
Hopefully you understand what i want to accomplish, is just that i havent found a good tutorial that shows this, how to repaint something x amount of times .. when I do Thread.sleep() it all stops then it shows my app.. but now i understand why, because i am playing with the main Thread.
Please help me understand this..
Thank you

i did something like this
animcolor()
{
Timer timer = new Timer();
int delay = ...;
int period = ...;
timer.schedule(new TimerTask(){
run() {
setColor( randomint() ); )
customview.postInvalidate();
}
}, delay, period);
threads? not necessary to create them; Timers make a good job on concurrency.
... and the code would somewhat look like....
res/layout/file.xml
<org.customviewlayout a:id="#+id/customlayout"/>
src/org.MyActivity.java
class MyActivity
{
onCreate()
{
customlayout = findViewById(R.id.customlayout);
customlayout.animcolor();
}
}
src/org.customlayout.java
import org.customview;
class customlayout
{
customview;
customlayout(context, attrs)
{
customview = new customview();
addview(customview); // so it's onDraw() method will be called
}
onlayout(...)
{
customview.layout(...);
}
animcolor()
{
Timer timer = new Timer();
int delay = ...;
int period = ...;
timer.schedule(new TimerTask(){
run() {
setColor( randomint() ); )
customview.postInvalidate();
}
}, delay, period);
}
setcolor(int)
{
....
}
}

i think, you can do this using a Timer and a TimerTask inside your activity. The TimerTask runs with the delay you specify and when run all you what to do is yourDrawShapeInstance.postInvalidate();
the mechanism is this, because you arent on the ui thread you call postInvalidate() to add an invalidate on the ui queue, when the ui engine pick the delayed invalidate that you invoke before, then calls automatically the onDraw method of your DrawShape view and the view will be redrawed.
(i don´t test this, i write here)
TimerTask task = new TimerTask(){
public void run(){
myDrawShapeInstance.postInvalidate();
}
}

When drawing, always use a thread away from the main thread and always invalidate after thread has finished (for the most part -- to display current results from drawing). You will probably call your drawing functions from some user-related event, so make sure you're making another thread for that drawing process. Follow those rules and you will be fine.
void drawCircleToCanvas(int color)
{
final Handler handler = new Handler() {
public void handleMessage(Message msg) {
myDrawShapeInstance.postInvalidate();
}
};
Thread updateUI = new Thread() {
public void run() {
//************draw something here***************
handler.sendEmptyMessage(0);
}
};
updateUI.start();
}

android assign a drawable dynamicaly to a imageview

I have an array of drawables, that I would like to change by my own timer to a imageview.
(i tried the other option with xml and setBackgroundResource, but does not work for me as I have hundret of pics and always got memory problem as it looks android assign already the whole memory for all pics at once. (just in this demo i shorted it to 4 images)
Ok, so first i make my array
private static int[] draws = {
R.drawable.frankiearmevor_0001,
R.drawable.frankiearmevor_0002,
R.drawable.frankiearmevor_0003,
R.drawable.frankiearmevor_0002
};
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
imgView = (ImageView) findViewById(R.id.fredi);
// create timer
Timer updateProgressTimer = new Timer();
updateProgressTimer.scheduleAtFixedRate(new TimerTask() {
#Override
public void run() {
myloop();
}
}, 0, 150);
}
int mycounter;
public void myloop()
{
mycounter++;
if (mycounter > 4) mycounter = 1;
imgView.setImageResource(draws[mycounter-1]);
String hallo; hallo = "now: "+mycounter;
Log.d("1",hallo);
}
when I assign only a fixed image: imgView.setImageResource(draws[2]);
it shows that fine and I see also my thread is logged fine, but when I exchange the
fixed resource draws[2] into a dynamic draws[mycounter-1] .. i just get a black screen, no error, nothing.
what to do, so i will show the images :)
thx
chris
EDIT: 22. August:
I tried now with the comment I got, it compiles fine, but somehow there is an error i guess.. it crash:
imgView = (ImageView) findViewById(R.id.fredi);
Timer updateProgressTimer = new Timer();
updateProgressTimer.scheduleAtFixedRate(new TimerTask()
{
#Override
public void run()
{
//myloop();
imgView.post (new Runnable()
{
public void run()
{
mycounter++;
if (mycounter > 10) mycounter = 1;
imgView.setImageResource(draws[1]);
//imgView.invalidate();
String hallo; hallo = "now: "+mycounter;
Log.d("1",hallo);
}
});
}
}, 0, 150);

The ImageView update should happen on the UI Thread...
Refer this answer. The TimerTask runs on a different thread, so you've to use the imgView.post() to update the UI Component.
Are you sure you need to update the Component every 150ms? That's very expensive.
Good Luck.