I have an array adapter which is used in my listview. The adapter is periodically updated by fetching or removing contents from a server. I have used a scheduledthreadpoolexecutor to periodically update the adapter and then use adapter.notifydatasetchange();
The list view gets refreshed and removes any items etc, but for example if two items where removed from the list when I scroll the listview on android and get close to the end of the listview the application crashes. I guess something does not get updated in the listview and it things that the size of the list is the initial size.
Do you have something to recommend?
Regards,
Aris
Hi all,
I actually found a solution to my problem and forgot to check here for any replies.
Thank you all for your suggestions.
Basically scheduledthreadpoolexecutor called a runnable (lets call it updateRunnable) to do the updates.
What I did was the following:
In the updateRunnable, when it gets the new data and stores them in the array adapter, it then calls another runnable (lets call it updateListView) using runOnUiThread and in updateListView I set the adapter of the listview.
This solved my problem
If your data is at all database-like, which I assume, given your use of a ListView, then you'll want to refactor your background service into a model that uses a ContentProvider and SyncAdapter to stay in sync with the server, and then automatically notify the ListView through binding it with a CursorAdapter which uses its implementation of ContentObserver to automatically update the list when the underlying DB changes.
Why does ContentResolver.requestSync not trigger a sync? tells you how to set up the ContentProvider.
How to handle REST calls, data persistence, syncing and observing ContentProvider tells you a little more about how list update notification operates once the ContentProvider is syncing.
It's a lot of infrastructure work to get set up, but once you do, there's so much that's wonderfully automatic about the SyncAdapter model.
I had a similar problem once. Since the ListView keeps updating you can
1) display the Listview just as the activity starts in OnCreate, and
2) call this SAME activity so as to display refreshed data in the listview.
but after calling the same activity again, finish() the current instance first immediately since you can get multiple instances of it one over the other.
Related
I have an activity that in onCreate calls an API and populates a RecyclerView with product names, current stock, and an EditText to insert a value for each product.
You can then hit an add or subtract button at the top of the activity and all products with an inserted value will have their stock updated in the database by the given values via the API.
I do not pass the on screen stock values to the API (as another user may have changed it in the meantime), simply the inserted values, product ids and whether to increment/decrement the database value.
Currently, after I send the update request and it is successful, I call finish() and just reload the activity to get the updated data.
I'm wondering if it would be better to make an API call for the data after the update request and then just update the RecyclerView, it would almost be duplicate code of the onCreate but would prevent reloading the activity.
Does anyone have any insight as to the efficiency of this vs reloading the activity? It seems like reloading would be the more inefficient option but i'm not too sure.
Assume in your onCreate method you have something like this:
onCreate() {
setContentView(xx);
callApiGetDataAndSetDataToRecyclerView();
}
If so, pls try to change the code like below after I send the update request and it is successful:
doAfterUpdateRequestSuccessful() {
List<Object> latestData = callApiGetData() // this should not be in the ui thread, I believe you are clear about it but just want to repeat
recyclerViewAdapter.setData(latestData);
recyclerViewAdapter.notifyDataSetChanged();
}
Then your recycler view will be updated with latest data.
And like #ADM's comment, finish and recreate the activity is never a solution for updating recycler view, the ux will be very very bad.
Reload the activity is not so efficient. You should instead move your fetch data and render logic to an independent method and invoke this method from onCreate and every time you want to refresh the rendered data.
I have question regarding my previous ListView activity.
I have my ListView which is continue updating using socket connection, now when I click on any of the list row i can go to my next screen now when i come back to my previous ListView screen my ListView is start updating again but i want to keep updating my ListView in a background when i am on my nextscreen.
Something like i want to keep my previous screen alive when i am on my nextscreen.
Sounds to me like your the code you are using to load the data for your ListView is tied to your Activity.
For instance you have an AsyncTask or Thread in your Activity that cointains your ListView and you use it to download data, or do whatever is needed to get the data to populate the list. I also assume you start it in one of the Activity lifecycle methods e.g. onCreate().
If that is the case then you should consider seperating the code used for getting the data for the list from your activity code.
One way to do this is to use a Service which will be able to run independantly of the rest of your application and do all the heavy lifting involed with fetching the data for your list. You can communicate with the service from anywhere in your application. The Service can save the data to a database. Then all you have to do in your Activity is query the database and populate the adapter to get the latest data without much delay.
You can read more about services here:
http://developer.android.com/reference/android/app/Service.html
You could (and probably should) do what Paul suggested or you could change to way you switch your screens by using Fragments or a ViewFlipper. This way you still run your AsyncTask or Thread while doing something else on a different page.
I will start with what I am trying to accomplish.
I have a ListFragment, with LoaderCallbacks associated to retrieve data from a DB. The data is downloaded using an AsyncTask, and inserted into the DB. When the user gets to the bottom of the list, using the CWAC-Endless widget the AsyncTask is kicked off and downloads more data.
I am facing a couple of issues here, and I have tried to sort this out over many a night, and I have decided to come here to ask for help.
The first issue is configChanges. When the user rotates the device, the Activity is destroyed, and then recreates all of the Fragments. I know I can use setRetainInstance to true, but this does not help as the AsyncTask is still running when the Activity gets torn down!
The second issue is to do with the Loader. If data is downloaded, and the AsyncTask completes fine, then the items appears in the List fine. Lets say there are 20 items in the DB. When the user rotates the device, and the Fragment is recreated, the Loader needs to be associated again. When this happens, the data is not loaded into the list straight away, and instead the AsyncTask for the download is kicked off because the CWAC-Endless adapter thinks its at the last item in the list!
Both of these issues have exhausted me. I need a fresh look on this, as im getting no where.
Any suggestions will do, and I can post up source code if needed.
EDIT
Ok here are a few more details to help with some suggestions.
I am downloading data from the internet, which will only return a set number of items at a time. I then have to request more data when I want it (pagination).
I decided to use a database, as the new Loader functionality makes it so simple to make sure the data is loaded efficiently and consistant, without any threading issues.
If it would make sense to ditch the Loader approach, and use a standard Adapter to render the data, I am more than happy to ditch this approach and use that. I just wanted to see if someone could offer an insight into why this solution is so difficult.
Thanks,
Adam
When the user gets to the bottom of the list, using the CWAC-Endless widget the AsyncTask is kicked off and downloads more data.
FWIW, I have not tried EndlessAdapter with this combination of stuff (cursors, loaders, and AsyncTask). In particular, quoting the docs:
Note that this has been tested with ArrayAdapter extensively but may not work with other adapter types
I am not even quite certain what the use case would be for an EndlessAdapter applied to a local database. If you have a crazy long list (e.g., thousands of rows), the answer isn't "load it progressively" but "provide a different UX to avoid the long list". For shorter lists, just load the whole thing and be done with it. EndlessAdapter is for cases where the loading is expensive (e.g., Internet access).
That being said, I will add "play with EndlessAdapter and Loader" to my to-do list.
I know I can use setRetainInstance to true, but this does not help as the AsyncTask is still running when the Activity gets torn down!
So? onPostExecute() will not be invoked until the new activity has gotten through onCreate(). Moreover, in a fragment-based model, your task should be talking to the fragment, and if that fragment is retained via setRetainInstance(true), it's the same fragment instance in both the old and the new activity.
When this happens, the data is not loaded into the list straight away
It should be loaded in fairly quickly, though asynchronously. Moreover, I don't see why this is any different from when the activity is created in the first place.
and instead the AsyncTask for the download is kicked off because the CWAC-Endless adapter thinks its at the last item in the list
You should not be creating the EndlessAdapter until after you have data.
I am looking to refresh a ListView without reloading the page. More precisely I have a service that is sending data for a ListView in an Activity, however the Activity loads long before the Service can get the data. So I need to be able to load/reload the ListView after the Activity has already loaded.
I found that notifyDataSetChanged only works if you use the add, insert, remove, and clear functions on the Adapter, so I ended up doing it the following way in a similar implementation:
An AsyncTask fetches all the data in doInBackground. Then, when finished I set the list adapter for the first time in onPostExecute. To let the user know that something is loading, I just put a TextView on top of the Listview and set its text to "Loading.." in onPreExecute and then make it invisible in onPostExecute when the data is ready.
If you need to refresh the data, you just execute the AsyncTask again.
I like this way because you are only setting the ArrayAdapter once (i.e. when you finally have all the data). Here is more on AsyncTask in case you need it. The docs have some nice example code.
Call notifyDataSetChanged() on the ListView's Adapter whenever you want to refresh it.
I would say to use IntentService instead of Service. By, using IntentService you will be able to send data to the background Service and also receive the updated data while firing a BroadCastReceiver to update your UI. Here is a complete example how you can achieve your task using an IntentService.
I have a simple personal application I'm working on that queries some records in an SQL Database and populates an adapter for a listview and is basically working fine... but I've began to wonder if I'm doing certain things at the right point of the framework.
Currently I'm loading everything up during onCreate(). In theory, I could be loading up quite a bit of data, so I wanted to possibly throw up a ProgressDialog while the information is being added to the adapter, but I ran into some odd threading issues with the Cursor. Ultimately, I launched a Progress Dialog near the end of onCreate(), followed by sleeping on another thread and calling a method to load my data with runOnUiThread() following the short sleep time, having the end of that method dismiss the Progress Dialog.
This works, but it's brought me to whether or not I should be loading database data during onCreate... or whether it should be moved to onStart() or onResume(), adding in code to clear the close and open the database, clear and repopulate the adapter as necessary as other Activity's are started and finished. Or would all that be unnecessary and I should just keep the adapter populated during onCreate()?
Reto Meier's suggestion to use an Application may suit your needs. Take a look at Activity restart on rotation Android
Move it to onResume, as if you stop the activity you can destroy the adapter and fill it back when to resume the activity.
It helps to save memory and also helps to update the adapter if data has changed.