Question

Let say I have my view that I use it as a toggle button. When user clicks it, I change the background via setBackgroundResource(). The number of list is around 15 items and ListView can show only around 7 items on screen.

At first, I try to use ListView.getChildAt(position) but when position is more than 7 it returns NullPointer. eventhough ListView.getCount() returns 15. But that’s make sense because it show only visible child.

Then I solve it by loop through all Data that binds to this Adapter, change the boolean value, and call notifyDataSetChange()

So the number of loop will be 15 for update data + 7 show visible view.

The best way should be 15 and that’s done.
Is there anyway to achieve this?

Thank

Answer 1

Forget your child index. You should just toggle some type of flag in your adapter.

Then when your getView method is called again it will redraw your list.

i.e.:

public class YourAdapter extends BaseAdapter {

   private boolean useBackgroundTwo = false;

   .. constructor ..

   @Override
   public View getView (int position, View convertView, ViewGroup parent) {

       ...


       ...


       View background = findViewById(...);

       int backgroundResource = R.drawable.one;
       if(useBackgroundTwo){
            backgroundResource = R.drawable.two;
       }
       background.setBackgroundResource(backgroundResource);



       ....
   }

    public void useNewBackground(){
       this.useBackgroundTwo = true;
       notifyDataSetChanged();
    }

    public void useOldBackground(){
       this.useBackgroundTwo = false;
       notifyDataSetChanged();
    }

}

Then in your activity code:

((YourAdapter) listview.getAdapter()).useNewBackground();

Taking it further, you could use an enum instead of a boolean and have multiple methods setBackgroundGreen(), setBackgroundRed() or you could pass in the drawable you want to use setItemBackground(R.drawable.one); The choice is yours.

Api: Adapter