Can anyone give me an example that uses onResume() in Android?
Also, if I want to restart the activity at the end of the execution of another, which method is executed—onCreate() or onResume()?
And if I want to update data, how do I put it in onResume()?
Any Activity that restarts has its onResume() method executed first.
To use this method, do this:
#Override
public void onResume(){
super.onResume();
// put your code here...
}
Restarting the app will call OnCreate().
Continuing the app when it is paused will call OnResume(). From the official docs at https://developer.android.com/reference/android/app/Activity.html#ActivityLifecycle here's a diagram of the activity lifecycle.
The best way to understand would be to have all the LifeCycle methods overridden in your activity and placing a breakpoint(if checking in emulator) or a Log in each one of them. You'll get to know which one gets called when.
Just as an spoiler, onCreate() gets called first, then if you paused the activity by either going to home screen or by launching another activity, onPause() gets called. If the OS destroys the activity in the meantime, onDestroy() gets called. If you resume the app and the app already got destroyed, onCreate() will get called, or else onResume() will get called.
Edit: I forgot about onStop(), it gets called before onDestroy().
Do the exercise I mentioned and you'll be having a better understanding.
When you open the app it will go through below states:
onCreate() –> onStart() –> onResume()
When you press the back button and exit the app
onPaused() — > onStop() –> onDestory()
When you press the home button
onPaused() –> onStop()
After pressing the home button, again when you open the app from a recent task list
onRestart() –> onStart() –> onResume()
After dismissing the dialog or back button from the dialog
onResume()
If a phone is ringing and user is using the app
onPause() –> onResume()
After the call ends
onResume()
When your phone screen is off
onPaused() –> onStop()
When your phone screen is turned back on
onRestart() –> onStart() –> onResume()
Happy Coding...#Ambilpura
Most of the previous answers do a good job explaining how, why, and when to use onResume() but I would like to add something about re-creating your Activity.
I want to know if I want to restart the activity at the end of exectuion of an other what method is executed onCreate() or onResume()
The answer is onCreate() However, when deciding to actually re-create it, you should ask yourself how much of the Activity needs to be re-created. If it is data in an adapter, say for a list, then you can call notifyDataChanged() on the adapter to repopulate the adapter and not have to redraw everything.
Also, if you just need to update certain views but not all then it may be more efficient to call invalidate() on the view(s) that need updated. This will only redraw those views and possibly allow your application to run more smoothly. I hope this can help you.
onResume() is one of the methods called throughout the activity lifecycle. onResume() is the counterpart to onPause() which is called anytime an activity is hidden from view, e.g. if you start a new activity that hides it. onResume() is called when the activity that was hidden comes back to view on the screen.
You're question asks abou what method is used to restart an activity. onCreate() is called when the activity is first created. In practice, most activities persist in the background through a series of onPause() and onResume() calls. An activity is only really "restarted" by onRestart() if it is first fully stopped by calling onStop() and then brought back to life. Thus if you are not actually stopping activities with onStop() it is most likley you will be using onResume().
Read the android doc in the above link to get a better understanding of the relationship between the different lifestyle methods. Regardless of which lifecycle method you end up using the general format is the same. You must override the standard method and include your code, i.e. what you want the activity to do at that point, in the commented section.
#Override
public void onResume(){
//will be executed onResume
}
KOTLIN
Any Activity that restarts has its onResume() method executed first.
To use this method, do this:
override fun onResume() {
super.onResume()
// your code here
}
Re-review the Android Activity Lifecycle reference. There is a nice picture, and the table showing what methods get called. reference Link google
https://developer.android.com/reference/android/app/Activity.html
After an activity started, restarted (onRestart() happens before onStart()), or paused (onPause()), onResume() called. When the activity is in the state of onResume(), the activity is ready to be used by the app user.
I have studied the activity lifecycle a little bit, and here's my understanding of this topic:
If you want to restart the activity (A) at the end of the execution of another, there could be a few different cases.
The other activity (B) has been paused and/or stopped or destroyed, and the activity A possibly had been paused (onPause()), in this case, activity A will call onResume()
The activity B has been paused and/or stopped or destroyed, the activity A possibly had been stopped (onStop()) due to memory thing, in this case, activity A will call onRestart() first, onStart() second, then onResume()
The activity B has been paused and/or stopped or destroyed, the activity A has been destroyed, the programmer can call onStart() manually to start the activity first, then onResume() because when an activity is in the destroyed status the activity has not started, and this happens before the activity being completely removed. If the activity is removed, the activity needs to be created again.
Manually calling onStart() I think it's because if the activity not started and it is created, onStart() will be called after onCreate().
If you want to update data, make a data update function and put the function inside the onResume(). Or put a loadData function inside onResume()
It's better to understand the lifecycle with the help of the Activity lifecycle diagram.
Related
While we are having onStart method, what is the purpose of onRestart method?
#Override
protected void onStart() {
super.onStart();
}
#Override
protected void onRestart() {
super.onRestart();
}
Here is the activity lifecycle there is your onStart() and onRestart() methods with explanations
more info here
One case of onRestart() being called is when user presses home button and comes to launcher screen. In this case, activity is not destroyed and pause/stop events are fired. When user opens your app again, onRestart() for that activity is called before onStart(). You can find example here.
The onRestart() method will be called whenever the Activity comes back from the invisible state. Suppose, we pressed the home button of the device and coming back, this onRestart() will be invoked. For more info about this, please go through the documentation
You can read all about the Activity's lifecycle on Android developers: http://developer.android.com/reference/android/app/Activity.html#onRestart()
Taken directly from there:
Called after onStop() when the current activity is being re-displayed
to the user (the user has navigated back to it). It will be followed
by onStart() and then onResume().
For activities that are using raw Cursor objects (instead of creating
them through managedQuery(android.net.Uri, String[], String, String[],
String), this is usually the place where the cursor should be
requeried (because you had deactivated it in onStop().
Derived classes must call through to the super class's implementation
of this method. If they do not, an exception will be thrown.
Only 100% sure that onRestart is called is when you navigate away and then navigate back to the activity.
On the other hand, when you press home button and the app moved to background, there is no way we can know whether the app is destroyed by OS to claim back resources or it is still reside on memory. If the app is destroyed then onCreate will be called. Otherwise if the app is still available in memory then onRestart will be called.
According to this
Note: Because the system retains your Activity instance in system memory when it is stopped, it's possible that you don't need to implement the onStop() and onRestart() (or even onStart() methods at all. For most activities that are relatively simple, the activity will stop and restart just fine and you might only need to use onPause() to pause ongoing actions and disconnect from system resources.
Called after onStop() when the current activity is being re-displayed to the user (the user has navigated back to it). It will be followed by onStart() and then onResume().
For activities that are using raw Cursor objects (instead of creating them through managedQuery(android.net.Uri, String[], String, String[], String), this is usually the place where the cursor should be requeried (because you had deactivated it in onStop().
onRestart() is called after onStop() when the current activity is being re-displayed to the user.
e.g. The user has navigated back to it.
Adding to NightFury's answer. The onRestart() method is a callback method in the Android Activity lifecycle that is called when the activity is restarting after having been stopped.
Some use cases:
If an activity is paused or stopped and the user returns to it, the onRestart() method can be used to resume the activity from its paused or stopped state.
In some cases, the onRestart() method can be used to refresh the data displayed in the activity. For example, if the activity displays a list of items that are fetched from a server, the onRestart() method can be used to refresh the list after the user returns to the activity.
When the configuration of the device changes (such as screen rotation), the onRestart() method is called. This can be used to update the activity's layout or other resources to accommodate the new configuration.
Error handling: If an activity has encountered an error and was stopped, the onRestart() method can be used to reset the activity and handle the error.
Please, help me understand activity lyfecycle more deeply. http://developer.android.com/guide/components/activities.html#ImplementingLifecycleCallbacks
They say:
The foreground lifetime of an activity happens between the call to
onResume() and the call to onPause().
Does this mean, that activity becomes resumed in some moment after onResume() is called, or after onResume() completely finished it's work?
Similar question about visible state and onStart.
And if the second is right (method completely finished it's work), then super.method() or overriden by me in activity class?
#Override
protected void onResume() {
super.onResume();
// is it now "resumed" after super.onResume()?
}
"The foreground lifetime of an activity" referes to the time it is directly being shown to the user. It also implies at the moment its process has maximun priority on the Android process priority ladder. You should read this http://developer.android.com/guide/components/processes-and-threads.html
Furthermore, onResume(), onPause()... are just hooks where you should insert code that needs to be executed on that specific moment of the activity lifcycle.
The foreground lifetime of an activity happens between the call to onResume() and the call to onPause().
Does this mean, that activity becomes resumed in some moment after onResume() is called, or after onResume() completely finished it's work?
Technically speaking, the Activity is in a state of being resumed before onResume() is called but the option for you to override the onResume() method allows you to fine-tune what needs to be done before the Activity enters the 'running' state. In other words, from the point of view of the OS, the Activity is resumed, then onResume() is called and, finally, from the point of view of your own individual app, resuming the Activity is complete when onResume() is complete and the Activity is running.
Similar question about visible state and onStart. And if the second is right (method completely finished it's work), then super.method() or overriden by me in activity class?
Again, the same logic applies - the OS goes through what it needs to do to start the Activity then calls onStart() for you to customise the starting stage of your Activity. The OS considers the Activity to have started before it calls onStart() but from your app's perspective, it hasn't completely become started until any code you have in your overridden onStart() method.
I have read documentation on onResume() and onStart() but one thing I'm still not cleared is under what scenario does onResume() get called without onStart() being called before it?
Please Refer to the Android Activity Lifecycle Documentation.
onStart is called when your application first starts.
If the user click the home button, or another app takes focus, onPause will be called.
If the activity regains focus, while stil running on the device, onResume will be called, and onCreate will NOT be called again.
If the user uses the activity manager to close the application, and then relaunches it, onCreate will be called again.
Note, every time onCreate is called, onResume is also called.
Check below chart:
In case your activity is visible but not active - onPause will be called, and then when you return to this Activity - onResume
One such scenario where onResume() is called without onStart() being called is change of Focus. Think about a dialog popping up on the screen while you're using the application. This is the case when onPause() is called, followed by onResume() after dismissal of dialog.
onStart() gets called once each time the app is launched and is actually called after oncreate()
onResume() gets called instead if the app is already running, just in the background.
if you use onPause(), on Resume will likely get called when you bring your app up again, basically onResume() is a reusable onStart() for when the app is already started.
onResume can sometimes be called when switching activities, onStart only gets called when creating one.
onResume() is called without onStart() when the activity resumes from the background.
This is a text I have copied and pasted from this training tutorial.
"Because the system retains your Activity instance in system memory when it is stopped, it's possible that you don't need to implement the onStop() and onRestart() (or even onStart() methods at all. For most activities that are relatively simple, the activity will stop and restart just fine and you might only need to use onPause() to pause ongoing actions and disconnect from system resources."
I don't understand it. Because to the best of my knowledge, an activity is only stopped by calling onStop() and is only started by calling onStart(). How can an activity start at all without an onStart method.
Do you people understand what they mean in this paragraph?
I think they are confusing you with the word "stop" which appears to have multiple meanings in the paragraph.
I would rephrase it as
Because the system retains your Activity instance in system memory
when it is not in the foreground, it's possible that you don't need
to implement the onStop() and onRestart() (or even onStart() methods
at all. For most activities that are relatively simple, the activity
will suspend and restart just fine and you might only need to use
onPause() to pause ongoing actions and disconnect from system
resources.
The point being is that the App can appear to be stopped, when in actual fact, the system has simply paused it and hidden it from the screen. When the user launches it again, the App doesn't need to start (because it technically hasn't stopped), so it is simply resumed.
When you make an Activity and extend the base class Activity, there is already code in the onStop(), onStart(), and onRestart() methods in the base class.
Your activity simply extends these methods, meaning that you could add more code to them by Overriding them.
So, even though Activities are only started and stopped through those methods, you do not have to explicitly override them in your application. In most cases you won't even have to worry about them: They will be called by the base class from which you are extending.
Please make sure, An Activity starts from onCreate method , then onStart is called by system. If you override onStart method then your overridden method will be also called after onCreate method. If you don't override , then default version of onStart is called.
onStop is called after onPause.
Please check this link , and take a look at Activity life cycle . Your concept will be clear.
Difference between onCreate() and onStart()?
you can use an Activity just fine without - if you need to do something special in onPause() you can override the method:
#Override
public void onPause(){
super.onPause();
// Your magic here!
}
Same goes for onStart(), onStop() etc. You don't need to override the methods but you can if you need to do something specific.
Is it possible that onPause() is called, and then immediately after that, onResume() is called? In other words, does the activity always has to go through onStop(), onStart() and then onResume() after its onPause() is called?
The activity lifecycle document says it is possible, but what would be the user actions to trigger that? Can anyone create an activity JUnit test to demonstrate that?
If Activity hasn't been fully obscured by another Activity then onStop won't be called
Yes, it is common for onPause() -> onResume() -> onPause() -> onResume() cycle to occur.
See the Activity lifecycle docs.
If an Activity is totally obscured (by another Activity for example) it will likely be stopped but if it is only partly obscured by another Activity (set with a dialog theme, for example), then it will simply be paused and then resumed when the 'popup' Activity is closed.
image here tell every thing nicely
Activity can go to onResume directly after onPause.