Enabling and Disabling ListView Item Constantly

Question

In my android application, I have an activity that creates a ListView. The ListView contains several items. Every item is associated with a specific condition. If the condition is met, the item should be enabled and clickable. Otherwise, the item should be disabled and non-clickable. To check the conditions constantly, I have a separate thread that keeps checking the condition for every item and updates the item view accordingly. My code is running with no errors, but the behavior of the item does not achieve my need. Sometimes, the item remains non-clickable even though its condition is met. Sometimes, the items are clickable even thought the condition is NOT met. Sometimes, the items behave correctly. Therefore, I believe I am implementing it improperly, which causes such non-deterministic behavior.

Below is part of my Activity:

menu = new ArrayList<String>();

//menu
//Critical Features
menu.add("View Patient Records");
menu.add("Search in File");
menu.add("Search Medicine");
menu.add("Search by Date");
menu.add("Search by Illness");
menu.add("Report");

//Important Features
menu.add("Identify Nearest Emergency");
menu.add("Identify District Emergency");

menu.add("Planning Intervention");
menu.add("Real-time Assistance");

//Useful Features 
listView = (ListView) findViewById(R.id.listView1);
listView.setClickable(true);



  ArrayAdapter<String> arrayAdapter =      
             new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, menu);
             listView.setAdapter(arrayAdapter); 


             listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {


                 public void onItemClick(AdapterView <? > arg0, View view, int position, long id) {
                     // When clicked, show a toast with the TextView text

Below is the part of the thread checking for conditions and updating the view:

            if(! condition)

              {             
                mainActivity.getListView().post(new Runnable()
                     {       
                         public void run()
                         {
                                View v = mainActivity.getListView().getChildAt(2);
                                v.setEnabled(false);
                                v.setOnClickListener(null);              
                         }
                     });

                  }


            if( condition)
            {


        mainActivity.getListView().post(new Runnable()
                     {       
                         public void run()
                         {
                                View v = mainActivity.getListView().getChildAt(2);
                                v.setEnabled(true);

                         }
                     });

        }

NOTE: The condition associated with the item depends on battery, network speed, network type.....etc. So the condition changes indeterminately, and the view can change constantly.

Answer 1

This sounds like its to do with the view recycling in android list views.

If your conditions are being updated periodically then you will need to create a custom adapter and have an up to date reference to check against each time getView is called from within your adapter.

Answer 2

Try to use scrolllistener.

listview.setOnScrollListener(new OnScrollListener(){
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
      // TODO Auto-generated method stub
    }
    public void onScrollStateChanged(AbsListView view, int scrollState) {
      // TODO Auto-generated method stub
if(! condition)

              {             
                mainActivity.getListView().post(new Runnable()
                     {       
                         public void run()
                         {
                                View v = mainActivity.getListView().getChildAt(2);
                                v.setEnabled(false);
                                v.setOnClickListener(null);              
                         }
                     });

                  }


            if( condition)
            {


        mainActivity.getListView().post(new Runnable()
                     {       
                         public void run()
                         {
                                View v = mainActivity.getListView().getChildAt(2);
                                v.setEnabled(true);

                         }
                     });

        }
}
}