Develop Reference

Android - onGlobalLayout is not called by ViewTreeObserver

I have a headache in current Android project. I want to detect the changing of the current page. For example, there is a TextView to display device time, which is updated per second. How to detect this change? I searched a lot on SO (thanks SO), but none works for me.
More information: I don't use standard Activity to create page. My way is:
All widgets are created into a View object which is then used to create a container object. After that, I just handle this container to draw on a canvas with a VSYNC callback Choreographer.FrameCallback periodically.
Indeed, it works to draw. All are ok. Except: I want to draw canvas only when the page's content changed. So back to my beginning question, how to detect this "changing" event? I am sure there is some kind of callback to handle this problem. I used the following solution, but onGlobalLayout is not called when textview's text changed.
CanvasAppViewContainer container;//CanvasAppViewContainer extends AbsoluteLayout
LayoutInflater li =(LayoutInflater)getService().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View view = li.inflate(resourceId, null);//passed a correct the layout id
container = new CanvasAppViewContainer(getService(), view, getWidth(), getHeight(), getSurface());
rootView = (LinearLayout) findViewById(R.id.rootView); //root element of layout
rootView.getViewTreeObserver().addOnGlobalLayoutListener(
new ViewTreeObserver.OnGlobalLayoutListener() {
#SuppressLint("NewApi")
#Override
public void onGlobalLayout() {
Log.d("test", "onGlobalLayout");
}
});
BTW: Even if I register the view tree observer for the textview, onGlobalLayout is still not called.
Thanks

onGlobalLayout() is only called when the layout changes. When you want to detect a change in the text use TextView.addTextChangedListener()

Show views currently focused (Even without layout selectors)

I'm trying to inspect a code for a very big Android (Amazon Fire TV) activity but i keep loosing the focus in the running app and i don't know what element is being focused.
I'm looking for a way (Wether it's an App, a developer setting - Show Layout Limits gets near - or something i can code inside the activity) to see what view is being focused, without having to change the layout (Selectors) of every single view.
What do you suggest?

Activity has a method called getCurrentFocus().
Maybe you could call hasFocus() on all the Views if the above doesn't work. I imagine the method would look something like this:
public View getFocusedView(View layout)
{
View focusedView = null;
// Note: I'm not sure if FOCUS_DOWN is the right one to use here
// so you may want to see the other constants offered
ArrayList<View> views = layout.getFocusables(View.FOCUS_DOWN)
for(View v: views)
{
if(v.hasFocus())
{
focusedView = v;
}
}
return focusedView;
}

Posting a runnable to a View that invalidates the View sometimes doesn't work

I been fighting an odd issue these last few days. I have a custom ExpandableListAdapter where each row contains an ImageView, among other things. I have a class that handles the asynchronous loading of images from the multitude of places they may reside (disk cache, app data, remote server, etc). In my adapter's getView method I delegate the responsibility of returning a View to the list Item itself (I have multiple row types for my group list). I request the image load as follows:
final ImageView thumb = holder.thumb;
holder.token = mFetcher.fetchThumb(mImage.id, new BitmapFetcher.Callback() {
#Override
public void onBitmap(final Bitmap b) {
thumb.post(new Runnable() {
#Override
public void run() {
thumb.setImageBitmap(b);
}
});
}
#Override
public void onFailure() {
}
});
Yeah, it's ugly, but I decided against some contract where you have the BitmapFetcher.Callback execute its methods on the UI thread by default.
Anyway, when I load the Activity that contains the ExpandableListView there will often be thumb images missing from different rows in the list. Reloading the Activity may cause some of the missing thumbs to show but others that were previously showing may not be anymore. The behavior is pretty random as far as I can tell. Scrolling the ListView such that the rows with missing images get recycled causes the new thumb images (when the recycled row gets displayed again) to load fine. Scrolling back to rows that previously contained missing images causes the missing images to appear. I can confirm that all the images are loading correctly from my BitmapFetcher (mFetcher) class. I should also mention that I load other images in other places. Every once in awhile they don't appear either.
After pulling most of my hair out, I discovered that changing:
thumb.post(new Runnable() {
to:
mExpListView.post(new Runnable() {
fixes the issue. I originally thought that the issue might be happening because I was using a final reference to a View, but the other locations in the app use non-final references to a view to post messages, and, as I mentioned, sometimes those did not work. I eventually changed everything to use an Activity's runOnUiThread() method (and my own getUiThreadRunner().execute method when inside Fragments) and that seems to fix the issue all around.
So my question remains, in what cases can View.post() to fail to deliver the runnable to the associated ViewRoot's message queue in the proper order? Or, perhaps the invalidate() is happening before the View is returned from getView and thus before it's placed in a ViewGroup that can be reached from the root View. Those are really the only cases I can think of that would prevent the image from showing up. I can guarantee that none of these calls are happening until at least onStart has finished executing. Further, it looks like it's fine to post to a View even if it hasn't been attached to a Window yet:
// Execute enqueued actions on every traversal in case a detached view enqueued an action
getRunQueue().executeActions(attachInfo.mHandler);
(in performTraversal). The only difference between the runOnUiThread and post seems to be that an Activity has a different Handler than the ViewRootImpl.
Activity:
final Handler mHandler = new Handler();
whereas in ViewRootImpl:
final ViewRootHandler handler = new ViewRootHandler();
But, this should not be a problem provided both Handlers were constructed in the same Thread (or using the same Looper). That leaves me wondering if it is, indeed, a problem to invalidate() a View that has not yet been added to the hierarchy. For this to be the case invalidate should either 1. not do anything if it's not visible, or 2. only be valid for the next performTraversal() that happens.
View.invalidate() checks a nice private method that's not documented called skipInvalidate():
/**
* Do not invalidate views which are not visible and which are not running an animation. They
* will not get drawn and they should not set dirty flags as if they will be drawn
*/
private boolean skipInvalidate() {
return (mViewFlags & VISIBILITY_MASK) != VISIBLE && mCurrentAnimation == null &&
(!(mParent instanceof ViewGroup) ||
!((ViewGroup) mParent).isViewTransitioning(this));
}
It looks like number 1 is more accurate! However, I would think this only pertains to a View's VISIBILITY property. So, is it accurate to assume that a View is considered not VISIBLE if it cannot be reached from the ViewRoot? Or is the VISIBILITY property unaffected by the View's container? If the former is the case (which I suspect it is) it raises a concern. My use of Activity.runOnUiThread is not a solution to the problem. It only happens to work because the invalidate() calls are being sent to a different Handler and being executed later (after getView returns and after the row has been added and made visible on the screen). Has anybody else run into this issue? Is there a good solution?

Hey David I ran into a similar issue long time back. The basic requirement for view.post(Runnable r) is that the view should be attached to the window for Runnable to be executed. However, since you are loading images asynchronously in your first case, therefore there is a probability that imageView aren't attached to window when post request is made and hence, some images fail to load.
Quoting earlier version of docs on the same:
View.post() : Causes the Runnable to be added to the message queue. The runnable will be run on the user interface thread. This method can
be invoked from outside of the UI thread only when this View is
attached to a window.
Switching to you next question, what is the best solution to handle this situation ?
Can't comment on the best solution. However, I think both handler.post() and activity.runOnUIThread() are good to go. Since, they basically post runnable in main thread queue irrespective of anything and in general, the request to display list rows would be enqueued prior to our thumb.post(). So, they might work flawlessly for most cases. (Atleast I've never faced a problem with them !). However. if you find a better solution, do share it with me.

Try this : setBitmap() like this :
runOnUiThread(new Runnable() {
#Override
public void run() {
thumb.setImageBitmap(b);
}
});

After loading an activity, it sometimes works, sometimes not, why?

I have a bit of a problem I cannot solve, since it might a bug or something like that. I would like to make a chart with androidplot, and it works really good, but of course it needs some time to draw it (using hundreds of data), so I use a progress dialog to indicate the loading. But what happens is really weird.
I can define the appearance of the activity when it's loading and when it's loaded. When its loading I define a textview in the background setting its text to "loading" and if it is loaded, that textview contains lots of datas, text etc.
onCreate
{
Thread thread = new Thread(new Runnable() {
public void run() {
-------what needs to be appeared after its loaded ----
Textview -> 12,3245,456,78,789
}
----what is on the screen while the progressbar is on---
TextView -> loading..
}
But most of the time after the progress dialog disappears, nothing happens, the textview still says "loading" and rarely it loads the datas and makes the data appear and changes the textview. What I noticed that the more data I would like to appear the rarelier it stays at the loading phase. Of course everytime the loading progessbar appeers then disappears.
Any Suggestion? It is really weird because I use it in a tablayout and other tabs never do this, always make the data appear.
Thanks in advance!
UP: Okay, its always the first tab, whatever it contains, so the first tab is somehow wrong...

The Andoid UI toolkit is not thread-safe. So, you must not manipulate your UI
from a worker thread—you must do all manipulation to your user interface from
the UI thread. Thus, there are simply two rules to Android's single thread model:
1. Do not block the UI thread
2. Do not access the Android UI toolkit from outside the UI thread
read this for more information on how to access UI elements from outside.
edit::
use AsyncTask ::
onCreate
{
new myLoading().execute();
}
class myLoading extends AsyncTask<Void, Void, Void>
{
protected Void doInBackground(Void ... ) {
.......... do all the loading here .........
}
protected void onPostExecute(Void ) {
Textview -> 12,3245,456,78,789
}
}

I figured out some workaround. I dont have any clue about the solution, my only guess is the loading screen somehow overtake the arrival of all the data and so the chart cannot be drawn. or whatever...
I put a thread.sleep(1000) and now it works.

Weird updateViewLayout behaviour

I have a view (custom drawn) added with getWindowManager().addView() and later I'm modifiying the LayoutParameters of it (changing x & width) and call getWindowManager().updateViewLayout(). This works but I am getting two screen refreshes, first one only moves the whole thing according to the new x and later one scales it according to the new width. Any ideas about why is this happening even though I only call updateViewLayout just one time with the new layout parameters?
FYI: onDraw method of the custom drawn view mentioned here is also called only one time by the system during this process.

Try:
runOnUiThread(new Runnable() {
public void run() {
view.updateViewLayout();
}
});
http://developer.android.com/reference/android/app/Activity.html#runOnUiThread(java.lang.Runnable)
If it doesn't work, check this:
How to move a view in Android?
Are you doing this?

try to do :
view.post(new Runnable() {
public void run() {
view.updateViewLayout();
}
});

updateViewLayout is an a method that can be overriden by your custom ViewGroup and in this overrided method you can implement all what your want to change.
Maybe you do something wrong in it?
Or also maybe you have to implement this code in UiThread like in other questions. - In this case when you change your parameters asynchronously with first call of drawing function by system you method maybe can change only one parameter and on second call the second parameter will be also changed.