I have made an app.
When I launch that app in the normal way, then it works fine. When I press the home button, the app is paused and is still there as it should be.
Now I want to start my app by an intent...so e.g. when a NFC tag is detected the app should launch. This also works, but when I am pressing the home button then the app disappears, but I would like that it stays open (in pause mode) like when I launch it in the "normal wayy". Does anyone know why this can happen? My observation is that the onStop() function is called but not the onDestroy() function. Therefore it is very strange that the app just "disappears".
Thanks a lot in advance.
Please see Android Activity Lifecycle. onDestroy() is not always called when application goes to background and generally here are no guarantee that onDestory() will be called before app/activity is killed.
Could you please explain what you mean 'pause mode'? You mean that app saves the state?
Related
I was trying to implement splash screen in android by adding time for which the splash screen is to be shown.
Whenever I close the app by pressing the back button it destroys the activity. If one open the app again from the recent screen it shows the splash screen, but it leads to bad user experience(as they are annoyed by seeing the splash screen again and again, it should only be shown when the user swip of the app from recent screen).
So I thought of adding onPause() and onStop() method inside onBackPressed() method but then the app is never destroyed(i.e. onDestroy isnever called).
How to solve this issue?
Here is the chunk of surprise:
None of the Activity Life-cycle Methods will be called when the app is swiped off
Swiping the app means killing the process of the app and hence it's dead. That's it.
Only onStop() will be called when we press the Recent App button near the Home button.
To implement SplashScreen to appear only for the first time, you can use Shared Preferences and maintain a data as this data will be in your app until the app is uninstalled.
Any other doubts regarding this, please post in comment. We will be happy to help.
I am starting a service in my app. On click of service I am launching an activity. The service click event works fine when we go to any app and press back button and exit the app.
But if we are in any app and then press home button and click on the service the activity is not launched. If I click it more then 2 times,it opens the activity and sometimes it opens the app also.
So i am unable to understand the difference between pressing back button and home button.
After you start an activity, if HOME key is pressed, then the current activity is stopped and its task goes into the background. The system retains the state of the activity - i.e. onSaveInstanceState will be called. If the user later resumes the task by selecting the launcher icon that began the task again, the task comes to the foreground and resumes the activity at the top of the stack.
However, if BACK key is pressed, the current activity is popped from the stack and destroyed. The assmuption is the activity is done and will not be used again. So the system does not retain the activity's state - i.e. onSaveInstanceState will not be called.
Home Task :
Pressing the Home switches you from the app to the home screen, whilst leaving your app running in the background. This is a bit like switching between windows on a Windows PC.
Except that when your phone is running low on resources like memory it will start to close apps that are running in the background, so that your phone has enough resources for what you're trying to do now. Games are often amongst the first apps the phone will "kill" to save resources as they often use a lot more memory and CPU than other apps. This is why sometimes your game is still running paused, and sometimes Android has closed it for you.
The Back button is the way to close apps so that they are actually closed.
onPause() is called in Activity A when it launches Activity B. After the back button is called in Activity B, onResume() is called in Activity A.
In case of activities their default implementation is LIFO based in stack and works like:
On Back button Pressed: finish the current activity by calling stop method.
On Home button pressed: activity is being paused and then it may either resume if come back to it, otherwise system will call stop() method of activity to save unused resources and utilize memory.
but these functions can be edited by overriding if required.
What exactly happens when I press home button in Android?
Because when I open it again after home button pressed, it has series of bugs.
I need to know it to track down the point that causes that bugs.
UPDATE:
when pressing home button, application goes to background and onPause() is called and saves the state of UI, however it does not save state of application, like variables, custom views. And you have to save them manually, as Oren explained.
When you press Home Button your Application/Activity goes in background and when you open it again it resume from the same position as it was until it was being killed/closed by the OS.
Activity Life Cycle will give you a clear idea about it.
Technichally? Anything can happen, from just onPause being called, to the device killing the app to free up memory, to the user shutting down and restarting the device. Your app should handle all of these possibilities.
Further reading : android activity lifecycle
I have a puzzling problem. If I deploy my application from Eclipse on any device/emulator, I can use the Back and Home buttons to minimize it and then I can click the launcher icon to resume it.
If I take the apk, put it on the phone and install it (using the Astro file manager), then press Back or Home, when I click the launcher icon again, my application will be recreated instead of resumed: the activity is not destroyed.
This goes against everything written about on the android developer website regarding activities and their lifecycle.
For instance, this is what I do when the user uses the Back button:
#Override
public void onBackPressed() {
moveTaskToBack(true);
}
Yet my application is recreated when I click its launcher icon. Any ideas?
This goes exactly with everything written about the activity life cycle.
If an activity is paused or stopped, the system can drop the activity
from memory by either asking it to finish, or simply killing its
process. When it is displayed again to the user, it must be completely
restarted and restored to its previous state.
http://developer.android.com/reference/android/app/Activity.html
You application is not "minimised". There is not such thing as minimised in Android. It's not Linux or Windows or OSX.
It's true, pressing Back will kill your Activity. However, why is that a problem? Android provides a mechanism to save your Activity's state and be able to resume.
View the Activity lifecycle: http://developer.android.com/reference/android/app/Activity.html#ActivityLifecycle
This is a must read on saving Activity state: http://developer.android.com/reference/android/app/Activity.html#SavingPersistentState
Using my mom's phone with my app if i hit the home button and then navigate back to the app, it is calling onCreate again. If I understand correctly this should not be the case right?
I know this is happening because my webview loads and it should just open up the page that was already open. Especially since I have the launch mode set to singleInstance...
What are some reasons to why it would be called twice on my mom's phone, but on my phone it works exactly how it should?
According to the Android documentation, your Activity can be killed at any time when it's not active which is the case when you switch back to the home screen.
If an activity is paused or stopped, the system can drop the activity
from memory by either asking it to finish, or simply killing its
process. When it is displayed again to the user, it must be completely
restarted and restored to its previous state.