Develop Reference

Is there an event that triggers when the app is closed?

As the title says.
Specifically, I am writing an app that prints data to files over the course of runtime. I want to know when I can tell my PrintWriters to save the files. I understand that I can probably do autosave every X minutes, but I am wondering if Android Studio will let me save on close instead. I tried using onDestroy but the code block never executed. (To be precise, I started the app, did a few things, closed the app, clicked Recents, and swiped the app away. The debugger showed that the app never got to that code.)
My current solution attempts to catch the surrounding circumstances by checking for key presses but this only works for the back and volume buttons and not the home, recent, or power buttons.
#Override public boolean onKeyDown(int key, KeyEvent event) {
close();
return false;
}

There's a built in hook to the Activity lifecycle to save your state- onSaveInstanceState. There's even a bundle passed into you to save your state into for it to be restored (the matching function is onResumeInstanceState). And as a free bonus, if you call super.onSaveInstanceState and super.onRestoreInstanceState, it will automatically save the UI state of your app for all views with an id.

Please check the activity lifecycle:
https://developer.android.com/guide/components/activities/activity-lifecycle
Or if you're using a fragment:
https://developer.android.com/guide/fragments/lifecycle
Consider using one of these two:
#Override public void onStart() {
super.onStart();
close();
}
#Override public void onPause() {
super.onPause();
close();
}

Is there any way to track what fragment/s are visible right now?

I work on a very large project. It has a lot of modules and views - activities and fragments. I need to understand what fragment and what activity are running at the moment. Then I need to move to this class of activity and fragment in the project. Is there any way to find the class name? maybe by logs or smth else?

You can use Android Profiler for this. You will also get a lot of details from this tool. Just hover the mouse over the graph, it will show the fragment currently showing.

You can try Layout Inspector, a feature of android studio. When the app is running on a device that is connected to Android Studio, you can click on any item to see the view id, you can use these ids to find out which activity/fragment they belong to (through xml file)

Use UserVisibleHint for that:
boolean isVisible;
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
isVisible = isVisibleToUser;
}
When you want to check the visibility of the fragment, simply check it.
if (isVisible) {
//Fragment is visible
} else {
//Fragment is not visible
}

How to show Online of a user?

I'm trying to get an app to show all the users online... I'm using the following way to achieve it
#Override
public void onStart(){
super.onStart();
mDatabaseReference.child("Online").setValue(true);
}
#Override
public void onStop(){
super.onStop();
mDatabaseReference.child("Online").setValue(false);
}
I'm not using ondisconnect because it shows offline only if the app is completely closed(not running in the background). SO i used this method on each activity... But the problem is that whenever i open an activity it shows online and the next second turns offline... I'm guessing that its because the prev activity closes after opening the new activity so the presents activity's on start is executed before the next activity's on stop. So since the activity's onstop is executed last it shows offline. How do i solve this problem

Your guess is completely correct.
Starting a new Activity will cause the onPause() and onStop() methods to be called for the first Activity.
Based on your description, I'm assuming that you want the Online status to remain true for as long as the app remains in the foreground and you are putting it in every Activity because your app doesn't only open from a single main Activity.
Your current code will work without a problem if you switched to using a Single-Activity Architecture, which is simply to use a single Activity and have it display different Fragments instead of new Activities. This solution will work with your existing code because onStop() and onStart() will only be called when your app enters the background.
If you look at the Navigation section in the official Android Developers Blog, you'll see that Google wants to encourage developers to switch to using the Single-Activity Architecture.
However, if you still wish to use multiple Activities, then you might want to consider an alternative way to keep track of Online status to take into account of multiple Activities.
For example, rather than using a simple boolean value, you can use an int value.
#Override
public void onStart(){
super.onStart();
mDatabaseReference.child("Online").addValue();
}
#Override
public void onStop(){
super.onStop();
mDatabaseReference.child("Online").removeValue();
}
With the addValue() and removeValue() being:
private void addValue(){
activityCount++;
onlineStatus = true;
}
private void removeValue(){
activityCount--;
if(activityCount <= 0)
onlineStatus = false;
}
Please keep in mind that this is only an example and doesn't take into account of how your app is designed. Bottom line is, you'll have to think of a solution that takes into account of multiple Activities that are displayed.
I do heavily suggest the Single-Activity approach.

Android AccessibilityDelegate force reading of ViewGroup not children

I'm using a viewpager which is made up of some number of relative layout siblings which are quite complex.
If I click on the relative layout, it will highlight the entire page and read the title and a few textviews one after the other as expected.
If I scroll the viewpager I'd like talkback to read the next page in the same way it reads the first if I click. Secondly, if I scroll to the second, third, etc. pages and click on those layouts, talkback will read as expected.
I am trying to achieve the click behavior after the scroll event has completed.
Here is what I have for the accessibilityDelegate.
viewPager.setAccessibilityDelegate(new AccessibilityDelegate () {
#Override
public boolean onRequestSendAccessibilityEvent(ViewGroup host, View child, AccessibilityEvent event) {
if (event.getEventType() == AccessibilityEvent.TYPE_VIEW_SCROLLED) {
View page = viewPager.getCurrentPageView();
performAccessibilityAction(page, AccessibilityNodeInfo.ACTION_CLICK, Bundle.EMPTY);
}
return super.onRequestSendAccessibilityEvent(host, child, event);
}
});
I've verified that 'page' is the RelativeLayout parent that I think it is. I've also confirmed that the onRequestSendAccessibilityEvent is being fired, but it doesn't read the contents of its children. Am I missing something?
Updated
I've also tried using
viewpager.getCurrentPageView().sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_FOCUSED);
The above worked for another example when I needed to force talkback to reread a single item but does not have any affect if I try it on the page.
Thanks

Some background -- When you tap on the relative layout, TalkBack generates speech based on the layout's contents. On ICS, this is triggered by a HOVER_ENTER event. On Jelly Bean, it's triggered by an ACCESSIBILITY_FOCUS event. These events are sent automatically by the framework and should, generally speaking, never be sent manually from an app. The same goes for FOCUS events, except in the special case of custom views (see Accessibility talk from Google I/O 2013 for more details).
So, back on topic.
You can control the speech for SCROLLED events by populating the outgoing event with the text you want read. The down side of this is that you'll need to manually generate the text you want read, and it's very likely that this text will differ from what TalkBack will read if the user touches the layout.
viewPager.setAccessibilityDelegate(new AccessibilityDelegate () {
#Override
public void onPopulateAccessibilityEvent(View host, AccessibilityEvent event) {
super.onPopulateAccessibilityEvent(host, event);
if (event.getEventType() == AccessibilityEvent.TYPE_VIEW_SCROLLED) {
event.setContentDescription(/** your text */);
}
}
});
Another option is to do nothing and let the user explore the view on their own. This is the preferred interaction model for Android accessibility.
Edit: Video URL is broken, Changed.

This issue was reported on google check
where ViewPager does not set AccessibilityEvent parameters properly
when scrolling.
But after releas of Android Support Library, revision 23.2.1 (March 2016) This issue has been resolved.
update Support Library to Android Support Library to 23.2.1

I had the same issue before. And now I add android:focusable="true" to the ViewGroup, the TalkBalk will read the ViewGroup, instead of its children

Remove Recent Apps Button From Navigation Bar

I am currently developing an app and I would like to have a little more control over it then usual without having to root the device.
I would like to remove the capability of the recent apps button in the navigation bar, or at least make it do something else from the default actions. Is there a way to do this? I'm sure there is since SureLock does the same thing.
Thanks
I have found a workaround for this on this website:http://www.juliencavandoli.com/how-to-disable-recent-apps-dialog-on-long-press-home-button/
you need to add this permission: android.permission.REORDER_TASKS
And add this code:
public void onWindowFocusChanged(boolean hasFocus)
{
super.onWindowFocusChanged(hasFocus);
if( !hasFocus)
{
ActivityManager am = (ActivityManager)getSystemService(Context.ACTIVITY_SERVICE);
am.moveTaskToFront(getTaskId(), ActivityManager.MOVE_TASK_WITH_HOME );
sendBroadcast( new Intent(Intent.ACTION_CLOSE_SYSTEM_DIALOGS) );
}
}

It is not possible to override the recent apps button.
There is no KeyEvent like there is for the Back Button, and as such this feature is not available.
See documentation here: http://developer.android.com/reference/android/view/KeyEvent.html

You may not be able to disable a button, but you can disable the app that is associated with it. I don't know how it is done, but I have seen kiosk app (for non-rooted devices) that disallow other apps from loading.