Android :: Previous Set Instance Variables Null When Activity Resumed

Apr 20, 2010

I am using an Application object to store app-wide instance data--data that I need to remain in existence for the entire lifetime of the app, so the Application class seems like the proper place to put it. I have just finished reading this thread http://groups.google.com/group/android-developers/browse_thread/threa... that goes into pretty good detail and receives confirmation from Googler hackbod as to how the Application class performs--and from that info it seems this strange behavior I am receiving should not be happening...

Basically, every once in a while when I resume my app in any of its Activities (it is still running in memory so onCreate is not called) I get NullPointerExceptions because instance variables in my Application class are returning null when I request them from my Activity (via a getter method in my custom Application class). It seems as if sometimes Android saves the states of my Activities but deletes all my instance variable data... This can't be an Android problem--there must be something wrong with my code.

Has anyone else ever ran into an issue of this kind? Any ideas as to what may be causing this? I'm not going to post my code here as that won't help anyone, but hopefully someone can point me in some helpful directions.

Android :: previous set instance variables null when Activity resumed


Android :: How To Tell A Thread From A Previous Instance Of Your Activity Has Finished

Oct 31, 2010

I'm writing a bitmap editor and I'm trying to write an autosave feature. When onPause is called, I write the application state to an autosave file. As this takes between 0.1s and 1.5s, I've been advised this IO operation be performed in a background thread.

In the onCreate method of my activity, I check to see if the autosave file exists and, if it does, I open it.

Are there any scenarios I have to consider where the user can somehow leave the activity, the autosave thread starts and the user can return to the activity before the thread has finished? If so, how can I detect this and wait for the thread to finish before I check the state of the autosave file?

I was going to make it that, when the user backs out of my activity, they're asked to wait a second while the data is saved. This seems OK, but I can't do this when my activity is interrupted by something like a phone call.

Also, I'm a bit confused about how multiple versions of the same activity can be started as this makes dealing with autosaving more complex. Is there a way to make sure only one instance of my activity is allowed to run at a time?

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Android :: Threads Cache Instance Variables?

Jul 3, 2010

I am starting to develop an Android App and have noticed the following behaviour in my test code (not yet designed the real app):

A thread that loops around doing Bluetooth IO accesses an instance variable that is declared in the enclosing class. That instance variable gets set to null by the GUI thread in the onBackPressed() method which also closes the Bluetooth socket which causes an exception in the IO thread (which is what I want).

The odd thing is that if I set the instance variable to null before I close the socket, the IO thread sees the null value, but if I close the socket first and then set the variable to null, the IO thread doesn't see the null value.

The instance variable is being used in a loop in the IO thread and it appears as if that variable is being cached while within the loop. So any changes to that variable by another thread are not visible. Is that possible? If so, is there a workaround to guarantee that the VM will read the value of the instance variable?

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Android :: Way To Detect Why Activity Was Resumed In Phone

Aug 24, 2010

I'm developing an Activity that does some of its own state management. I'm trying to differentiate the following onResume cases:

New launch
task switch (home button long-click)
resume after other activity in the same application
wake-up after sleep
orientation change

Is there something in the Activity's intent, or elsewhere, that can help me differentiate these?

For the curious and some context... I'd like to preserve my internal history stack on 4 & 5. On cases 2 & 3, I would preserve the same current page, but erase the history (allow the normal back button functionality to take over at that point). Case 1 would initialize to the activity's internal start page (and can be detected easily enough with some help from ocCreate).

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Android :: Activity - Sometimes - Throws Wrong State Class Exception When Being Resumed After Kill

Nov 24, 2009

I'm testing how my app behaves when killed by the OS due to low memory conditions. I always have three activities on the stack, like: A B C (then C launches maps or some other heavy process)

when my app is killed, and I return to it, C starts itself up again ok. When I hit the back button to go to B, I [sometimes] get an exception thrown which I can't trace. Output is below. I don't know where to go from here. I've only seen one other post mentioning this exception, but it was related to a reproducable error when rotating the device. This only happens sometimes.

CODE:....................

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Android :: Finish Any Previous Activity In Stack From Current Activity?

Apr 27, 2010

How to finish any previous activity in application stack (at any level , I mean not immediate parent) , from current activity like on some particular event I want to invalidate this previous activity?

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Android :: Current Activity Force Closes - Tries To Go To Previous Activity

Nov 5, 2010

The default behavior from my observation is if current activity force closes Android tries to go to previous activity on stack How can I control this behavior? I want force close to close all activities

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Android :: How To Get Calling Activity Instance From Called Activity?

Jul 9, 2010

I have a Contact Activity which is derived from ListActivity, which displays list of contacts, and on click of item, a new Activity Message Activity derived from ListActivity is initialized.Now I know, I can pack some information in Bundle and pass it before creating activity, but is there a way I can get instance of "ContactActivity" in onCreate method of "MessageActivity"?

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Android :: Data Of Previous Activity Gone When New Activity Starts

Dec 30, 2009

I am developing an application in which the user require to register first and than got the user page. For that i have made layout and the layout consist many fields, so, i have made part of layout and also made the separate activity for the each layout. The layout like address, phone, etc... After that i have wrote the code for calling an activity and it works fine. It means when i press the "Next" button the another page will come and it will also consist some textview ,edittext and previous and next button. Actually, i want something different like -- When the user fill the first form and he will proceed to next, the content written by the user should not gone when the user press "Next" button. The content should be there which was written by user. And same way i have have 6 pages like that way to complete the registration process. So, have you any idea to solve above problem? I really need your help because right now i stuck at this point. So, please any body help me out of this problem. I would appreciate your help. I am waiting for your reply.

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Android :: Activity Lifecycle And Static Variables

Jul 14, 2009

I just ran into a situation where it looks like a static variable reference is persisted across activity sessions. I didn't expect that because I thought that when an activity exits, it's de-referenced and garbage collected. I am wondering if anyone can shed some (more) light on when the VM eliminates object references for Activities and Services and in particular when static variables get reset to default values?

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How To Pass Variables From Service To Activity

Aug 30, 2012

how can I pass variables from service to activity and vice versa?

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Android :: Handle Existing Instance Root Activity Launching Root Activity From Intent Filter

Apr 3, 2010

I'm having difficulties handling multiple instances of my root (main) activity for my application. My app in question has an intent filter in place to launch my application when opening an email attatchment from the "Email" app. My problem is if I launch my application first through the the android applications screen and then launch my application via opening the Email attachment it creates two instances of my root activity. steps: Launch root activity A, press home Open email attachment, intent filter triggers launches root activity A Is it possible when opening the Email attachment that when the OS tries to launch my application it detects there is already an instance of it running and use that or remove/clear that instance?

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Android :: Get Instance Of The Activity?

Jul 9, 2010

Is there a way to get an instance of the activity that has called the currently running activity from the intent object that has been passed to it? eg. if A has called B, I would like to retrieve A's instance from the intent in B's onCreate method. As Activity is not Serializable i am not able to pass the instance in the extras bundle.

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Android :: Recover An Instance Of An Activity

May 9, 2010

I have a bunch of tab activities (which I implemented myself, didn't want to use the tabviews with activities inside them), so It's basically 5 activities calling each other every time the user clicks on the tabs displayed as a row of LinearLayouts at the bottom of the screen.

The thing is that the way I do it now, everytime the user jumps from one activity to another, a new activity is created and launched. Of course, I can see I'm wasting resources this way. So what I would like to do is to create every activity only once; and then if the user wants to go back to the previous (or any one that was already created and is probably paused) just check on some kind of list or array to see if the activity can be recovered and only in the case it can't; to lauch a new one.

My question is, how can I check this? should I save the intents? and how to recover the activities afterwards? I'm kind of new with java.

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Android :: Get Instance Of The Launched Activity

Jul 19, 2010

Is there any way to get the instance of a launched activity(or any view in that activity )of a application in another application.

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Android :: How Finish An Activity In This Instance

Aug 16, 2010

We all know that hitting the back button on the device doesn't kill the application, it merely finishes (destroys) the activity running on the foreground.

Well I have come across some code which helps me capture the back button signal so that I cannot exit the application. The only way to exit it in such cases is to press the home key.

Now this situation presents me with a unique disadvantage! The inability to kill finish the application on a time of my own choosing allows the application to keep running in the background like nothing has changed.

So in such cases is the task manager my only friend or is there a way for me to otherwise kill this application?

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Android :: Push New Instance Of Main Activity?

Sep 2, 2010

Is it possible to create/push-onto-stack a new Activity of the same main Activity in an Android application with an argument passed to the Activities constructor? Specifically from a Dialog object...

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Android :: PendingIntent Always Creates New Activity Instance?

May 21, 2010

My app consists of an Activity and a service that runs in the background. The service periodically checks a website for an alarm condition. When the service detects the alarm, it should put a user notification into the status bar. If the user clicks the notification, it should display the app's activity. If the activity is already running, that activity should become visible. If the activity is not currently running, it should be created.

However the notification created by my service *always* creates a new instance of the activity, whether the activity is currently running or not. How do I get the desirable behavior?

Here is my service pseudo-code:

CODE:...............

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Android :: App Opens Previous Activity / Only Intermittently

Jul 24, 2009

This is an intermittent bug in one of my apps. I don't expect anyone to solve it immediately, but I'd appreciate any thoughts on how to start debugging!So, my app lets users edit an item (in the EditPage activity). When they press the Back key, the desired behaviour is that it saves their edits and returns them to the home page (the HomeList activity). The code for this is below. It works fine. Except.The bug is this. Some users report that sometimes when they reopen the application after a pause, they are seeing *not* the home page, where they left the application - but the previous edit activity. Crucially, they are also seeing the edit activity without their saved edits - effectively losing their most recent edits.I've been able to reproduce this myself. It only happens after the application hasn't been opened for a while. If I save something, minimize the application and reopen it straight away, it shows the HomeList activity just fine, and the edits have all been saved. But if I save something, leave it for a couple of hours and then reopen it, it shows the previous EditPage activity, without the saved edits (i.e. in the state that the EditPage activity was previously launched).

Any ideas, anyone? I had wondered whether it was due to the Back button being used to return the user to the HomeList activity - maybe Android thinks that the Back button means that the HomeList is not the most "recent" activity, instead the EditPage is. I'd like to carry on using the Back button if possible, though. And in particular, I'm puzzled why it only happens after the app has been idle for an hour or so, and not immediately? Is it something to do with Android's memory management?

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Android :: Previous App Launches Not Starting Activity

Jun 2, 2010

I need a way to detect if this is the first time the user is ever opening the application, if so, start an activity. Then all previous application launches wouldn't start that activity. I've read in a few places about using preferences to accomplish this. Anyone got any ideas?

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Android :: Stop Mediaplayer From Previous Activity

Feb 16, 2010

Can anyone tell me how to stop media player that was started in a previous activity?For ex. In activity-1 button pressed that did - mp.start(); then activity-2 starts for different layout with new buttons, then when button pressed, mp.stop is called, but does not stop the media from the first activity.

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Android :: How To Store Previous Activity Value In Droid

Dec 16, 2009

How to store previous activity value in android

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Android : Pass Values From One Activity To Previous?

Jul 14, 2009

Can any one tell me how to pass the value from one screen to its previous screen. Consider the case.i m having two screen first screen with one Textview and button and the second activity have one edittext and button. If i click the first button then it has to move to second activity and here user has to type something in the textbox. If he press the button from the second screen then the values from the textbox should move to the first activity and that should be displayed in the first activity textview.

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Android :: Correctly Manage Activity Stack In This Instance?

May 28, 2009

I'm working to finish a small application, but I'm having problems seeing what combination of activity attributes and intent flags I need to achieve my intended application design. Trying my best not to describe the app in minute detail, here's the basic operation (I've supplied screenshots in the hope it makes sense easily): Users have a garden which contains flowers (GardenActivity).

http://www.tomgibara.com/images/daisy/garden/hut_screen.jpg

They can tap on a garden to see details of flowers (FlowerActivity)

http://www.tomgibara.com/images/daisy/garden/flower_screen.jpg

When flowers are fully grown a notification provided, tapping on the notification displays the garden containing the flower.

http://www.tomgibara.com/images/daisy/garden/notify_screen.jpg

Users can also use the GardenActivity as a picker to choose flowers to "exhibit" (ConfigureActivity)

http://www.tomgibara.com/images/daisy/garden/planting_screen.jpg

I want the app to operate so that if the user already has a GardenActivity somewhere in the stack (whether it's at the top, or underneath a FlowerActivity) the notification will alert the user by bringing that activity to the front (clearing any FlowerActivity that may be above it). I've tried using the FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TOP combination (without changing any activity launch modes) on the notification's pending intent, but it still launches a new GardenActivity, even if one is already available.

I've also tried using android:launchMode="singleTask" on GardenActivity. The notifications then seem to work correctly, but it prevents GardenActivity from returning any result back to ConfigureActivity.

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Android :: Prevent New Activity Instance After Clicking On Notification

Jun 24, 2010

Application (non-wanted) behavior - application is started, some text is put into text-box and notification is created through button action. user "clicks" the home button, application is "minimized", notification is available in bar user selects the notification and the application is "maximized"

BUT - instead of the original instance, new instance is started (e.g. in the newest instance is missing the original text; when the latest instance is closed there is still the original instance with original text ) .

The code of the notification method

CODE:.....

I have also in the manifest xml file following tag android:launchMode="singleTask"

But it is still the same...The main problem is double/triple initialization of the application, i know that there are other means to preserve the values in resumed applications. Also it is needed that the applications stays running in background as the main functionality is the streaming of internet radio.

What is missing in the code ? What kind of information from my side is missing for to troubleshoot the issue ?

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Android :: Saving Cursor State With Activity Instance?

Apr 27, 2010

I've got an android app that pulls a random 20 questions (rows) as a cursor from a SQLite DB and loops through all the questions to ask the user all 20 questions.

Is there some way to save the cursor's state/location when the activity is paused or stopped so that when the activity resumes the cursor is restored and in the same position as it was when the activity was paused/stopped?

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Android :: AllowTaskReparenting - True Will There Be A Single Instance Of The Activity

Oct 4, 2009

Before asking my doubt, let me clarify my understanding of allowTaskReparenting...

Suppose there exists a Task (say Task 1) and this task has an activity (say Activity 1) which wants to call my Activity (say Activity 2). Let my activity (activity 2) set the attribute allowTaskReparenting to true and let my activity have a specific taskAffinity(affinity1). When Activity1 calls my activity (activity2), my activity becomes part of the task1. But suppose another task (task2) is already present/created with the same taskAffinity as mine (affinity1) and an activity in that task (say activity3) tries to start my activity, my activity gets re- parented to task2.

Not sure if i was clear enough. If i were to rephrase my words...

If my activity has allowTaskReparenting set to true and an instance of my activity is already present in task1. If task2 with the same task affinity as my activity tries to start my activity, the EXISTING activity gets re-parented from task1 to task2.

My quesions:

(1) Is my understanding correct ?

(2) If I am correct then a single instance of my activity gets shifted from task1 to task2. So 2 activity objects of my activity are NOT created.

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Android :: New Activity Instance Created For Every Intent-filter?

Feb 6, 2010

I'm using an intent-filter on URLs for my activity:

CODE:...............

the launchMode attribute is set to "singleTop", but it looks like a new activity is created every time I click a matching url. I thought that if the activity is already alive somewhere, it would simply be brought to the front of my activity stack?

I tried this on the emulator/device, same behavior, a new activity instance is always created.

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Android : Single Instance Theme Of An Activity In Phone

Sep 7, 2010

I have two activities. A and B. A starts B. Both are running in the screen and both are visible. Say now B is visible.

On a special key press, I want to bring the A to the front and make it active. The problem I am facing is when the special key is pressed, another instance of A is launched and the new instance is brought to the front.

But I want the original A to come to the front. I want to make this change in the framework layer rather than application specific by using the singleInstance theme in the launchMode in AndroidManifest file.

Please help me in this regard as this is really urgent for me. Any inputs will be really valuable for me.

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Android : Inside TabActivity / How To Get Instance Of Current Tab Activity?

Apr 23, 2010

I have attached a menu to my TabActivity, and when a menu item is selected, I would like to do something different based on which view is being currently displayed in the TabHost.

int getCurrentTab() returns me the id of the current tab... but from that int how can I get the instance of the activity running?

I also tried getCurrentView(), getCurrentTabView(), but these return things I can't seem to cast to the class of the current activity.

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