I have a Fragment that contains a ListView that uses a custom adapter that extends ArrayAdapter. Each item in this list view, contains another ListView that also extends ArrayAdapter. Think of it as a list of news stories and each news story having multiple images.
I now want to add a new image to a news story. What I do is:
ImageAdapter imageAdapter =
newsAdapter.getImageAdapterForNewsItem(id);
imageAdapter.add(imageId);
imageAdapter.notifyDataSetChanged();
This all happens in SelectImagesFragment, where as the news items are listed in the NewsItemsFragment. However, the SelectImagesFragment contains a reference to the NewsItemsFragment. The above code executes in an AsyncTask, and before it executes, I move the user back to the NewsItemsFragment.
I was expecting the news list to get updated, once the AsyncTask completes and the UI to get refreshed. However, this is not happening. Since the ImageAdapter is inside the NewsAdapter, do I need to somehow tell the NewsAdapter that there has been a data change as well? If so, how do I do this? Calling 'notifyDataSetChanged()' won't work, since I didn't modify the underlying list data in NewsAdapter using add().
Related
I have viewPager() which have 3 pages, it have a recyclerView and each page have three different adapters and i want something like when user clicks on adapter item in first page it adds in a database and second adapter gets its array list from the same database, but it shows in second page's adapter after app restarts, so the question is how to update the second page's adapter without restart.
A regular ListView can use a CursorAdapter which provides some of the functions you need. Alas, there is no existing CursorAdapter class that extends RecyclerView.Adapter.
The quickest solution would be to use RecyclerViewCursorAdapter on GitHub.
Then it would work something like this:
Update your database
Get a reference to your second page fragment. You can store this reference when you create the fragment in getItem(). Note that your fragment could be null depending on what pages the ViewPager has/hasn't created.
Call a method on your fragment that will create a new Cursor to be used by the adapter (with the same query as before). When the adapter receives the new Cursor it will update the RecyclerView.
I am trying to display a list fragment in the middle of my activity. The list fragment adapter is a custom adapter (extended from BaseAdapter) with the typical ViewHolder pattern. It is implemented correctly.
I have the adapter set up with greenrobot Eventbus to receive a new List object from an asynctask which does the query in the background (as not to slow down the UI Main Thread).
The problem is the list fragment doesn't have the results of the database query initially so it defaults to empty (and displays the textview in my xml for the main activity which has the id 'empty').
In the end, my adapter, and listviewfragment don't get instaniated at all because it defaults to empty.
Is there a better method to doing this?
How can I get my listview fragment to wait for the data recieved from the asyncTask?
I am going to just do a fragment with a listview in it, instead of a listview fragment, and I'll see if that will help.
As I understood correctly, you did everything okay so far. What you have to do is to add an "update" method to your adapter, and call this whenever your asynctask finished it's job and got the results for you.
This update method should look something like
public void updateAdapterData(List<String> newList) {
mItems.clear(); // say mItems is the global list you have in the adpater
mItems.addAll(newList);
notifyDataSetChanged(); // This will cause the adpater to re-draw it's rows, so now data should be visible in your list
}
And in your fragment you do somehting like:
adpater.updateAdapterData(newList);
Does this help?
I have a fragment class extending ListFragment and I'm having trouble populating the list.
I run an asynctask to retreive and parse data from a webservice which is all working ok but now I'm stuck on where I should set the list adapter to populate my list.
I am currently executing my asynctask in the onCreate() method and trying to populate the list in onActivity created which gives a NullPointerException. If i remove the setListAdapter everything runs fine.
According to the android developer docs, a fragment extending ListFragment returns a ListView from onCreateView() by default so I should have access to it.
Where is the correct place to set my list adapter to populate the list?
Thanks for your help.
You are going to want to set the list adapter in the onPostExecute() in the AsyncTask. You can pass a reference to the ListFragment into the constructor for AsyncTask and call setListAdapter() on that reference.
I have the following situation:
I have a singleton controller which contains a List<Foo>
when my activity starts I load the items to my BaseExpandableListAdapter
the problem: When I now delete a item form the singleton List it gets net deletet in the view. Only when I start the whole activity again. How to solve this without starting the whole activity again?
public void notifyDataSetChanged ()
Added in API level 1
Notifies the attached observers that the underlying data has been changed and any View reflecting the data set should refresh itself.
http://developer.android.com/reference/android/widget/ArrayAdapter.html#notifyDataSetChanged%28%29
When you change the database that is used by the adapter, you should call notifyDataSetChanged() on the adapter.
In the document for the method notifyDataSetChanged of class BaseAdapter noted that "Notifies the attached observers that the underlying data has been changed and any View reflecting the data set should refresh itself."
Supposed I changed the 3rd element in my string array (array data for the ListView), what "any View reflecting the data set should refresh itself" means ? Does the 3rd view item in my list view be notified ?
Also, how is notifyDataSetChanged() and getView() concerned ?
Supposed I changed the 3rd element in my string array (array data for
the listview), what "any View reflecting the data set should refresh
itself" means ?
It means that any view which shows/is based on/uses that data(the string array in your case) should be invalidated(remeasured, redrawn) in order to show the user the new set of data.
Does the 3rd view item in my list view be notified?
No, the parent ListView will be notified. When you set the adapter on a ListView, an observer(from the ListView) will be set for that adapter. Calling notifyDataSetChanged on the adapter will announce that observer from the ListView that something has happen to the data. At this moment the ListView will recreate the rows to show the new data.
Also, how is notifyDataSetChanged() and getView() concerned ?
I'm not sure I understand what you ask. The getView method of an adapter is used by the ListView to obtain a new row each time this is required. When you call notifyDataSetChanged on the adapter this will trigger the observer in the ListView. As it's time to recreate the list, the ListView will call the getView method of the adapter to show the necessary number of rows(the ones visible on the screen). So each time you call notifyDataSetChanged the getView method will be called for the visible rows.