Android :: Singleton Objects To Save State Or Share Data Between Activities?
Nov 24, 2010
It would be nice if StackOverflow had a section where we could post tutorials like mine so that I can answer literally hundreds of questions that have been asked here with a single blow. See... every day I read questions about how to pass complex objects between activities, how to save state so that your app can resume after orientation change, how to update listviews when the data changes, etc, etc. Here is the second part of a tutorial series I posted on my blog... I hope that you actually read it... because I haven't seen any examples like it anywhere... and it has changed how I think about developing for Android across the board. The question is... is there a downside or negative affect of developing like this?
Beyond Smart Lists - How Observable Singletons change the game. Please read through both of these tutorials carefully... I will answer any questions about it here that I can... I really want to know what you think about this and if it might solve issues for you. NOTE TO MODERATORS: there are no advertisements of any kind on my blog.. so don't just close this because you think I am spamming somehow... I am not going to duplicate my post here.
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Jul 29, 2010
What is proper way to exchange data or objects between different Android Activities?
Welcome screen <-> Main Screen <-> Startup routines <-> Processing data <-> Settings
Is it normal/recommended to have more than one activity in Android app? in my opinion, it's somehow strange to have this model of data exchange inside application
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Nov 16, 2009
I am trying to pass a custom object to one activity from another. What I would like to use is the HashMap of WeakReferences, but the description isn't clear, at least to me. From above URL: "A HashMap of WeakReferences to Objects. You can also use a HashMap of WeakReferences to Objects with Long keys. When an activity wants to pass an object to another activity, it simply puts the object in the map and sends the key (which is a unique Long based on a counter or time stamp) to the recipient activity via intent extras. The recipient activity retrieves the object using this key."
MyObject object = new MyObject(); HashMap map = new HashMap(); WeakReference reference = new WeakReference(object); map.put(reference.hashCode(), reference);
Intent i = new Intent(myIntent); i.putExtra(map);
I know this is probably way off but I can't figure out how this is intended to be implemented based on the description. Are the keys hashcodes, user defined, or what? It sounds like all that is passed is a HashMap containing the key values but how is the object retrieved with just the key? I couldn't find any code examples or useful documentation on this method of passing objects
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Oct 26, 2010
The FAQ mentions a method of passing objects around activities. (It is not clear to me): "A HashMap of WeakReferences to Objects. You can also use a HashMap of WeakReferences to Objects with Long keys. When an activity wants to pass an object to another activity, it simply puts the object in the map and sends the key (which is a unique Long based on a counter or time stamp) to the recipient activity via intent extras. The recipient activity retrieves the object using this key.".................
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Mar 25, 2009
I have two services, both of them lies in separate apk, which run in same process. The two service share same jar file by <uses-library> method. The jar file implement a class, say "test", is a singleton. But I found that two instance of test is created under this case, could anybody give me some tips? I want to ensure it's singleton. Code...
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May 4, 2012
Is there a better way then using titanium backup and manually doing this? Seems like a crazy tedious thing to do. I jump back and fourth between the two devices even on an hourly basis. one is my phone and the other is a tab.
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Aug 30, 2010
I want to pass an object from Activity B to Activity A. Scenario:
- Activity A calls Activity B
- User selects item in Activity B
- Activity B passes an object to Activity A
How do I accomplish this? And in which method do I read in the passed object in Activity A?
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Aug 12, 2010
I have a member variable in my Activity which is an ArrayList. The objects populating this Array List are objects I have defined called Rating Item. Rating Item has several member vars like rating, comment, ID, etc. I would like to save this Array List in onSaveInstanceState so it can be repopulated from onRestoreInstanceState. What is the best way to do this? I've never saved the state of an object of this complexity.
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Oct 18, 2009
I am trying to pass a user defined object to another activity Bundle bundle = new Bundle(); bund.putSerializable("myData", myData); intent.putExtra("bundle", bundle); where myData class implements Serializable interface. I am getting following error: java.lang.RuntimeException: Parcelable encountered IOException writing serializable object how to pass complex objects between activities?
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Jan 11, 2010
I have written my application logic in domain objects (to enable multiple user interfaces and porting to other platforms), and am now lookng at implementing Activities for the user interface.
Considering that each activity needs to serialise its state, what is the best way to ensure my domain objects are only serialised once?
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Jun 29, 2010
How to pass socket, inputstream, outputstream objects between activities
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Aug 27, 2010
Android: i want to create service by extending a Service class which i start when application get started and all activities can share its state and when i want stop it from other activity and when i want start it again from any activity ?
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Feb 14, 2009
I have two activities in two different packages: com.foo.a and com.foo.b. Is it possible to create an PreferenceActivity (with the exact same XML file) so that the preference is shared across the two activies?
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Jul 1, 2010
Is there any way to share the same object of the View across various activities? For example myApp has 4 activities, and every activity shows a Logo at the top of the screen. Now each activity will initiate 4 copies of the same Logo. So is there any way to get around this? And if 3 out of 4 share the same logo?
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Jun 30, 2010
how to call BarCodeScanner, and return the value to a field.so now, i have a toast that says "successful scan" and then i want to pass the result to a new activity. when i comment out my intent, everything works (minus the passing of data/switching of screen, obviously) but when i run my project as is, it FC's no errors reported by eclipse in code or xml. any insights?
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Dec 31, 2009
Is there any reason not to use the Application class to share variables across Activities? For instance a handle to the DB or a single HttpClient.
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Jul 20, 2010
I am developing an app which requires me to write to an SQLiteDatabase in one activity and access it from another activity . I am facing a problem implementing this. Any suggestions/ideas as to how we can share the database across multiple activities?
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Mar 16, 2010
I would like to share a cache file across activities, which are running in different processes but in a same application.So, is there any way to make it thread safe (probably not "thread safe", should we call it "activities safe" or "process safe" ?
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Aug 31, 2009
We have an Activity which has a form on it and we launch an Intent to take a picture.We've overridden onSaveInstanceState and onRestoreInstanceState to push the data from the view fields But, on the return from the CameraActivity, the onRestoreInstanceState method is never called. Should this behavior work when calling another Intent?
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Sep 1, 2010
can someone helpme out with how to save state of the app when the screen orientation is changed i read the development guide at http://developer.android.com/guide/topics/resources/runtime-changes.html#HandlingTheChange
But i dont know how to define the method collectMyLoadedData();
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Aug 30, 2010
I am writing an app where I get all the data from the rest call and display all the data in a custom component list(based on Linear Layout) which is added to a LinearLayout. I write this code in onCreate of the activity. The problem is when I switch activity using startActivity, and come back to the calling activity (using startActivity) then onCreate is called again. I see onPause, onStop called when I call other activity. Is there any way that I can save the application's state?
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Jul 16, 2010
I am developing an android application in which,the first activity is that for Login. After successful authentication, user can see an activity with 4 Tabs. My problem is that when user taps on the home button,the application should terminate and when the user again starts my application, he should be able to see the Login screen again and after successful Login, user should be able to see the tab on which he was working before application terminated(i.e., save state for all the tabs).
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Aug 9, 2010
I've encountered a problem wile using my own subclass of android.app.Application. I have numerous activities in my application and I'm running a custom ROM which consumes quite a lot of memory. What happens is when I launch a third party activity (Camera) my Application is killed. My Application subclass stores vital data for the whole app so it can't work without it. android.app.Application doesn't have any methods for saving or restoring application state. Activity does have them but they are not suitable.
How to perform save/restore state on Application subclass?
UPDATE I've managed to do so by filling a Bundle obtained from onSaveInstanceState and restoring values in onCreate. But is there any better way?
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Sep 4, 2010
In a previous question I asked how I could display two different layouts for portrait and landscape orientations:
Problem switching to landscape orientation
Now I would like to know how I can save the state of my application before it goes into another orientation? I seem to lose this data any time orientation changes.
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Oct 12, 2010
I was looking at the way Android handles orientation change for my application (I discovered that it restarts the mainactivity on orientation change :| ). I've seen that you can ovveride the method protected void onSaveInstanceState(Bundle outState)to save stuff, then have the in onStart. The problem is that I've my view with custom objects and a listview using a custom adapter... Everything is in a ArrayList of these objects, but I've noticed that you can't put arbitrary objects in the bundle! So how do I save the state?
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Sep 24, 2009
I wonder what is the right way to implement this? Could anybody advice whether my solution is correct?
So:
Activity is created
User clicks on button and dialog is launched (Dialog, not dialog styled activity)
User opens keyboard
we have onSaveInstanceState called where we save that our dialog was opened and all respective dialog input
we have onRestoreInstanceState and here we check whether dialog was shown, recreate the dialog with respective input.
Is it the right approach? or there is smth. that is done by Android and I am doing some redundant actions.
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Jan 22, 2009
In an ActivityUnitTestCase I'm trying to do:
CODE:...............
But on the save state call I get this trace:
CODE:.................................
Going through the ApplicationContext source code I've found this (http://tinyurl.com/d8qsyc):
CODE:...................
It seems the problem is that the activity token is not set. But here I'm puzzled, I don't know where to go next. Any ideas on how to fix it or workaround it are appreciated. I want to test that my application is saving its state correctly.
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Jul 1, 2010
I have an Activity, which contains a bunch of check boxes and a submit button.
When the submit button is clicked, the activity will exit (finish() will be called). Before the activity exits, I want to save the states of the check boxes in the activity, so when the activity starts again, the check boxes can stay in their previous states. What's the correct way to save these states? Should I use SharedPreference.
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Jan 11, 2010
As a follow on from my question on sharing state between Activities, how can I save the instance state of my Application? Since Application does not extend Activity, there is no onSaveInstanceState method to override.
NB: In advance, this is not a duplicate. Despite its name, How do I save an Android application's state? relates to Activity state
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Apr 30, 2010
This is a bit complicated to explain (and my first post), so bear with me please: I am currently trying to figure out the best way of saving my application's state in a bundle on the onSaveInstanceState event (working on a game). My application's state is based on a "world" class which contains various objects. Among these objects there is a creature object which contains bitmaps (Bitmap object)(allowing me to draw the various sprites of the creature when it's walking with more flexibility and accessibility).
Bit of creature constructor Java:
CODE:.................
After looking around for a few hours I found that serializing the world object (and all its sub-objects) was an acceptable way of saving it in the bundle. Unfortunately it appears that we can't serialize bitmaps and considering they're a part of my "creature" I can't seem to see a workaround.
Here come my questions: 1- Am I doing something fundamentally wrong? (not supposed to save bitmaps in objects? supposed to handle bitmaps in a separate class which I don't pass on the bundle and reload my bitmaps when restoring the application? ...) 2- Is there another way of passing my "world" object into my bundle (would using Parcelable work?)
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