I have an application with basically a list of items and a detail screen for each items.
When initially started, we show the list of items. If the user switches to another app when viewing a details screen, when he comes back to the app, the details screen is shown.
All that is the standard, and working well. However, my client needs the user to come back to the list screen instead of the details screen each time the app is resumed.
My first idea would be to remember the time at which the details activity got paused, and when started, if the time is greater than X seconds, finish and launch list activity instead of resuming.
Any more reliable way to do that?
PS: I know we should not do that, I already explained that to my client, decision is not mine.
Use SharedPreference to save the time of your paused detail activity in onPause and when it resume check the saved time with current time whether it has passed your threshold if it is passed then close it otherwise remain it opened.
Implement this solution and it definitely helps.
Basically, the app is not actually restarting completely, but your launch Activity is being started and added to the top of the Activity stack when the app is being resumed by the launcher. You can confirm this is the case by clicking the back button when you resume the app and are shown the launch Activity. You should then be brought to the Activity that you expected to be shown when you resumed the app.
The workaround I chose to implement to resolve this issue is to check for the Intent.CATEGORY_LAUNCHER category and Intent.ACTION_MAIN action in the intent that starts the initial Activity. If those two flags are present and the Activity is not at the root of the task (meaning the app was already running), then I call finish() on the initial Activity. That exact solution may not work for you, but something similar should.
Here is what I do in onCreate() of the initial/launch Activity:
if (!isTaskRoot()
&& getIntent().hasCategory(Intent.CATEGORY_LAUNCHER)
&& getIntent().getAction() != null
&& getIntent().getAction().equals(Intent.ACTION_MAIN)) {
finish();
return;
}
for more details on isTaskRoot()method reference.
You have to provide the following onPause() method to all the activity classes except your list_item activity(Initial Activity).
#Override
protected void onPause() {
super.onPause();
Intent i = new Intent(getApplicationContext(), list_item_activity.class);
startActivity(i);
}
I might understand your problem incorrectly but why you do all the timing stuff? I mean, assuming you've fragments for your list and detail views, just put a a flag to monitor your activity has stopped and listen to catch your activity resume ( via onResume or onWindowFocusChanged ). If it's stopped and resumed then transition to list fragment if it's not already visible.
You can you a broadcast receiver here.
And on activity OnResume method use a call to broadcast receiver and perform whatever you need like this.
#Override
protected void onResume() {
super.onResume();
sendBroadcast(new Intent("YourActionHere"));
}
Related
This is harder than it sounds, which is why I'm asking for solutions.
Basically I only want the disclaimer Toast shown once per run of the app.
The app is in two parts, all are Activities.
It's shown when it starts in the first part, but you can hit a menu button
taking you to the second part of the app, which has another menu button
to take you back to the first.
The problem is that whatever initial settings you try to make in the first
part, when it starts up, are run again when returning from the second
part of the app, so it'll show again.
My last idea was that in the first part's onDestroy(), when the app exits, but is not the case in this situation, you set a boolean in settings,
to reset that the disclaimer can be shown, but apparently, onDestroy() is called on the first part before it goes to the second part.
Or, if you can get it to not show the first run, but behave properly
every time after that, that would be okay.
And there doesn't seem to be any method to be called when the app truly
is "killed", if there was that would be the way to do it, you could reset it there. Or if there was a method that was only called when the app first started..
Thanks!
You just need a boolean flag. Say we call it disclaimerShown. In onCreate() of Activity A, we check both the Intent Bundle and the savedInstanceState Bundle for this flag.
You can add the boolean to a Bundle when launching the Intent to start Activity A from Activity B.
If the user is in Activity B and presses the Back button to return to Activity A, you can override onBackPressed() in Activity B and include your flag there as well (though you'll have to catch this flag on onActivityResult() in Activity A).
If system initiated process death occurs in Activity A, the system will call onSaveInstanceState(Bundle bundle). So you add your flag to this bundle as well.
And if system initiated process death occurs in Activity B, you have nothing to worry.
And that handles all possible cases.
An elegant solution for this problem would be the ProcessLifecycleOwner.
This class provides callbacks to the lifecycle of your whole app (not individual activities) and you could use the Lifecycle.Event.ON_CREATE callback to show your toast once. Look at this stackoverflow question for a usage example of the ProcessLifecycleOwner.
It turns out that I already had an Activity that started before
my "Activity A", and I moved my disclaimer Toast there
and it works fine. You can't beat that simplicity lol.
Thanks for your answers!
I have 2 activities, a 4 digit pin style login Activity (MainActivity) and a content Activity.
This app stores private information and such that should not be able to be seen when resuming an activity, therefore i want the app to completely restart on the login activity each time it's launched, rather than picking up where it left off.
I've tried messing around within the content activity's onStop() and onResume methods, but these seem to be highly unreliable as sometimes when i have the onRestart setup to relaunch the login activity, it won't launch it at all, and calling for the login screen to be activated in the onStop() will prevent me from being able to finish up tasks in the background, such as saving data.
Is there anything i can add to the manifest file that will tell the app to restart from the login activity no matter what? One of the worst things that can happen when working on an app like this is that the information is accessible to someone other than the owner that wasn't forced to login..
What you need is to focus on two calls in your Content Activity:
onPause(): This is where you kill Content activity and remove it from the stack. You can do this easily:
#Override
public void onPause() {
super.onPause();
//Save your data here
finish(); //Kill Contect Activity.
}
onRestart(): This is where you redirect the user to the Main Activity.
#Override
public void onRestart() {
super.onRestart();
Intent i = new Intent(this, MainActivity.class);
startActivity(i);
finish(); //Kill Contect Activity.
}
This graph might help you in understanding the Activity lifecycle:
What you need is setting the flag android:clearTaskOnLaunch and android:excludeFromRecents for your activities in the Manifest.
I have two activities; let's say A and B. In activity A there is a broadcast receiver registered that listens for a particular event which will finish activity A. I am registering the broadcast receiver in onCreate(), and destroying it in onDestroy() of activity A.
For simplicity, there is one button in activity B named "Destroy Activity A". When a user clicks on button, activity A should be destroyed.
Normally all of this is running smoothly without any issues,but the problem occurs in following scenarios:
1) Suppose I am in activity B and i press the Home key to move the application to the background then if i use other resource-heavy applications, Android system will kill my application to free memory. Then If I open my application from recent tasks, activity B will be resumed, and it's onCreate(), onResume() etc method will be called. Now I press button to destroy activity A, but activity A has already been destroyed, so activity A's onCreate(), onResume() etc methods will not be called until and unless i go to activity A by pressing the back button. Thus broadcast receiver is not registered to listen for the event.
2) The same problem will arise when user has selected "Don't keep activities" from Developer options in the device's settings.
I have been looking to solve this issue for a long time, but i am unable to find a proper answer. What is the best way to handle this scenario? Is this an Android bug? There should be some solution for this issue.
Please help me.
If your Activity A has destroyed by Android OS itself then there are
no way to track.
Some people has suggested to track that Activity A by listning event in onDestroy method BUT if your Activity killed by system OS then note here it wont call those method .
This cannot be fixed while keeping your current broadcast logic.
Killing activities from the backstack, imo, is not a correct approach. You should strongly consider changing the logic of your navigation.
But if your project is big and time is a problem, and refactoring is out of the question, A.J. 's approach works, but you mentioned that you have lots of activities that needs to be killed, his solution becomes very tricky to implement.
What I suggest is the following. This might not be the best idea, but I cannot think of another. So maybe that could help.
You should have the following:
A Base Activity for all your activities.
A ArrayList<String> activitiesToKill object at the application level. (If you did not extend Application you can have it as static variable
First we have to make sure that the activitiesToKill is not lost when the OS kills the app in low memory. In the BaseActivity we save the list during onSaveInstanceState and restore it in the onRestoreInstanceState
#Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putSerializable("activitiesToKill", activitiesToKill);
}
private void onRestoreInstanceState(Bundle state) {
if (state != null) {
activitiesToKill = (ArrayList<String>) state.getSerializable("activitiesToKill");
super.onRestoreInstanceState(state);
}
}
The idea here is to save which activities should be killed in the list, by using their name.
The logic is as follow:
Let's say you have Activities A, B, C, D and E
From Activity E, you press the button and you want to kill B and D
When you press the Button in E, you add the names of B and D to the activitiesToKill object.
activitiesToKill.add(B.class.getSimpleName()
activitiesToKill.add(D.class.getSimpleName()
In the onCreate method of the BaseActivity, we have to check if the
if(savedInstanceState != null)
{
//The activity is being restored. We check if the it is in the lest to Kill and we finish it
if(activitiesToKill.contains(this.getClass().getSimpleName()))
{
activitiesToKill.remove(this.getClass().getSimpleName())
finish();
}
}
Make sure to remove the name of the activity if it is killed through the broadcast.
So basically this is what happens in every scenario.
If the app is running normally, and you click the button, the broadcast gets sent and B and D will get killed. Make sure to remove B and D from the activitiesToKill
If the app was killed and restored, you press the button, the broadcast will have no effect, but you have added B and D to the activitiesToKill object. So when you click back, the activity is created and the savedInstanceState is not null, the activity is finished.
This approach consider that activity E knows which activities it has to kill.
In case you DON'T know which activities to kill from E, you have to modify this logic slightly:
Instead of using an ArrayList use a HashMap<String, bool>
When Activity B is created, it will register it self to the hashmap:
activitiesToKill.put(this.class.getSimpleName(), false)
Then from Activity E, all you have to do is set all the entries to true
Then in the on create of the base activity you have to check if this activity is registered in the activitiesToKill (the hashmap contains the key) AND the boolean is true you kill it (don't forget to return it to false, or remove the key)
This ensure that each activity register itself to the HashMap and Activity E doesn't have top know all the activities to kill. And don't forget to remove them in case the broadcast kills them.
This approach also ensure that the activity is not killed when opened normally from an intent because in that case onSaveInstanceState would be null in the onCreate, so nothing will happen.
More advanced checks can be accomplished in case you have groups of activities that needs to be terminated through different conditions (not only a button click) so you can have a HashMap of a HashMap to divide them in categories.
Also note, that you can use getName instead of getSimpleName if you have multiple activities with same name but different bundles.
I hope my explanation is clear enough as I wrote it from my head, let me know if any area is not clear.
Best of luck
One of the main rules with Activities is you can't rely on any activity being alive except the foreground activity. The thing you're trying to do with broadcasts has nothing to do with back stack -- back stack doesn't guarantee all activities are alive at all times, but it will make sure they're recreated when it's time to go foreground.
In your example (if my understanding of what you're aiming to do) you need to navigate to something underneath A -- say, Activity Z, and the stack looks like this: Z-A-[B]. There's normal course of events where you hit back and it takes you to A, then after another hit -- to Z but in a certain case (say pressing a button) you want to move back to Z bypassing A -- this is a classic case to use FLAG_ACTIVITY_CLEAR_TOP and launch Z explicitly:
Intent intent = new Intent(this, ActivityZ.class);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
This will finish both B and A, and deliver the intent to Z. You will, probably also need the FLAG_ACTIVITY_SINGLE_TOP flag, pay close attention to the description of FLAG_ACTIVITY_CLEAR_TOP, there's some trickery you should consider.
I don't know if it's possible to handle this on a "proper" way.
What it comes to my mind, is to flag the A activity in some way. You can't use startActivityForResult() because you will receive the result before onResume() is called i.e. UI was already inflated.
If you using an Otto, you could try with a sticky event. Otherwise you will need a singleton to handle the flag or save it to shared preferences.
You will have to check that flag on your onCreate() method before calling setContentView(), if the flag is true just finish the activity.
With the information you have given, how about you register the broadcast in onCreate of Activity B after checking if its registered already or not. If onDestroy of Activity A has been called in either of the scenarios you have mentioned, then the deregister of the Broadcast would have been called. So in that case, you can register your Broadcast in onCreate of Activity B, so that you can listen to it, even if you have only the Activity B in your backstack.
Have you considered using Sticky Broadcast?
Also you can register your receiver on application level (in manifest) and listen to this event regardless of Activity A state.
But, like already said Youssef, killing activities from the backstack is not a correct approach. You should strongly consider changing the logic of your navigation.
Many solutions came to my mind but as you have not provided much information about your app, so I think this should work in general.
Instead of firing a broadcast to kill Activity A, just execute the following code when the "Kill Activity A" button is pressed in Activity B.
Intent intent = new Intent(getApplicationContext(),
ActivityA.class);
intent.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
intent.putExtra("EXIT", true);
startActivity(intent);
Add the following code in activity A
#Override
protected void onNewIntent(Intent intent) {
super.onNewIntent(intent);
if (intent.getBooleanExtra("EXIT", false)) {
finish();
}
}
protected void onCreate(Bundle savedInstanceState) {
//Ideally, there should not be anything before this
super.onCreate(savedInstanceState);
if(getIntent().getBooleanExtra("EXIT", false)){
finish();
return;
}
In the manifest set "singleTop" launch mode for activity A.
<activity
android:name=".ActivityA"
...
android:launchMode="singleTop" />
This will have the following consequences:
If Activity A is already running it will brought to the front of the activity stack and finished, thus removing it from the stack.
If Activity A has been destroyed but still present in the activity stack (to be launched when back button is pressed), it will be started, brought to front and finished, thus removing it from the activity stack.
If Activity A has already has already been destroyed and not present in the activity stack, and you still press the "Remove Activity A" button, it will be started, brought to front and finished.
Generally, you should not see any flicker.
Based on this idea, you may build a better performing solution for your particular app. For example, you may use the FLAG_ACTIVITY_CLEAR_TOP and finish the Activity A in onBackPressed() of Activity B.
The books I have are abysmal at explaining how to work with the lifecycle, there's a lot I'm missing that I'm hoping somebody can fill in.
My app structure is that when it's first started, it starts an activity full of legalbabble that the user has to accept. When he says 'ok', I start my main activity and then I call finish like this:
public void onClick(View view) { //as a result of "I accept"
Intent mainIntent = new Intent(mParent, EtMain.class);
startActivity(mainIntent); // Start the main program
finish();
}
Then in EtMain in the onCreate method, I've got some tabs and I instantiate some classes:
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mTabHost = (TabHost)findViewById(android.R.id.tabhost);
SetupTabs.setMyTabs(mTabHost, this);
mComData = new ComFields(this); // Create the objects
mDepWx = new WxFields(this, DepArr.Departure);
mArrWx = new WxFields(this, DepArr.Arrival);
mDepVs = new DepFields(this);
mArrVs = new ArrFields(this);
mTabHost.setOnTabChangedListener(new OnTabChangeListener(){
}
Questions:
The 'finish' in the first fragment should terminate the legalbabble activity so it'll never be restarted, right? And the EtMain one will remain forever (until killed externally), even if my app gets pushed to the background, right?
The way it is now, when EtMain gets pushed and later brought to the foreground (by tapping on the icon), it goes through the legalbabble screen as though it's a complete start - that's what I'd like to prevent - going thru the legalbabble screen again.
It would seem that I'd want to override onRestart in the second code fragment and put something in there to restart the app, right? That's the part I'm unclear about.
My question then is what needs to be done in onRestart. Do I have to recreate all the tabs and data in the tabs and all my object instantiations? Or is the memory state of the app saved someplace and then is restored back to the state that it was in before something else was brought to the foreground in which case not much needs to be done because all the objects and listeners will still be there?
Yes after the first activity has ended you shouldn't have to view that activity again. You could also write to the shared preferences that the user has previously seen legal info.
If you're UI object creation is in the onCreate method, this should only be called once. Pausing or resuming will not call the onCreate method again.
Unless you explicitly remove your objects and tabChangedListeners in the onPause method, you should not have to touch them in the onRestart method.
Correct, the state of the app is saved automatically. You shouldn't have to touch the onRestart method.
Hope this helps!
I think the problem is that the launch activity in your manifest is the legalbabble activity, so when you click on the icon, the system launches another one. A better architecture would be to launch the legalbabble activity it from your EtMain activity in the onCreate method of the latter, using startActivityForResult. From the docs:
As a special case, if you call startActivityForResult() with a requestCode >= 0 during the initial onCreate(Bundle savedInstanceState)/onResume() of your activity, then your window will not be displayed until a result is returned back from the started activity.
When you get the result in onActivityResult, you can call finish() if the legal stuff was declined; otherwise everything will proceed normally.
This avoids the problem that the launch activity defined in your manifest finishes when the legal stuff is accepted.
EtMain will not remain forever, if the user backs out (by pressing the BACK key) the Activity will be finished (onPause, then onStop, then onDestroy will be called).
In general you can ignore onRestore until you are doing something complicated.
Once the user has exited your application and re-enters (or presses the icon on the Homescreen), onCreate (followed by onStart and onResume) will be called for your first activity, so you do not need any logic in onRestart, your code in onCreate will do the setting up for you as it did the first time. Because of this your legal babble will appear again when the user starts the app after exiting unless you store a preference (in SharedPreferences or a database or file) to indicate you have already displayed it - in which case finish it straight away and start the main activity.
onRestart is only called when the application goes from the stopped state (onStop has been called but not onDestroy) to the started state (onStart is called but onResume has not yet).
For saving data - some components save their state automatically (e.g. EditTexts remember the text in them, TabHosts remember the currently selected tab etc). Some components will not. If you wish to save extra data then make use of onSaveInstanceState and onRestoreInstanceState. You should only use these methods to restore the state of your application or temporary data, not important things, e.g. the id of the resource what the user was looking at, what zoom level they were at etc. For things like contacts or actual data you should commit these changes to a database, SharedPreferences or other permanent storage (e.g. file) when onPause is called.
I recommend taking a look at the Android Activity lifecycle if you are confused. Or ask more questions!
My application starts with a welcome screen Activity, but that screen has an option to skip that screen altogether in future launches.
What's the proper Android way to do this? Initially, I just automatically detected the skipWelcome preference and switched to the 2nd activity from Welcome. But this had the effect of allowing the user to hit the back button to the welcome screen we promised never to show again.
Right now, in the Welcome activity, I read the preference and call finish() on the current activity:
SharedPreferences preferences = getPreferences(MODE_PRIVATE);
boolean skipWelcome = preferences.getBoolean("skipWelcome", false);
if (skipWelcome) {
this.finish();
}
And then I implement onDestroy to move on to the next Activity:
#Override
public void onDestroy() {
super.onDestroy();
startActivity(new Intent(Welcome.this, StartFoo.class));
}
But this makes for some weird visual transitions. I'm starting to think that I need a base Activity that pops open Welcome only if proper, and then goes to StartFoo.
I can't comment on Mayra's answer or I would (not enough rep), but that's the correct approach.
Hidden in the Android documentation is this important phrase for Activity.startActivityForResult(),
"As a special case, if you call
startActivityForResult() with a
requestCode >= 0 during the initial
onCreate(Bundle
savedInstanceState)/onResume() of your
activity, then your window will not be
displayed until a result is returned
back from the started activity. This
is to avoid visible flickering when
redirecting to another activity."
Another important note is that this call does not block and execution continues, so you need to stop execution of the onCreate by returning
if (skipWelcome) {
// Create intent
// Launch intent with startActivityForResult()
return;
}
The final piece is to call finish immediately in the welcome activity's onActivityResult as Mayra says.
There are a few solutions to this.
Did you try just launching the activity and finishing? I vauguely remember that working, but I could be wrong.
More correctly, in if(skipWelcome) you can start the new activity for result, then when onActivityResult is called, immidiately finish the welcome activity.
Or, you can have your launcher activity not have a view (don't set content), and launch either the welcome activity or StartFoo.