从活动中更新viewpager中片段中的列表视图

Question

I understand that this is quite a common issue, and I have referred to many different other questions but I still can't get this to work.

My activity implements a view pager with two tabs and in each tab is a listview. I have a adapter for my view pager which links the two fragments and in each fragment, a adapter to link the data to the listview.

In my activity menu, I have a menu which creates an edittext in an alertdialog for me to input new fields into one of the listview in one of the fragment.

My activity (contains a viewpager)

protected void onCreate(Bundle savedInstanceState)
{
    ...
    subAdapter = new SubAdapter(getSupportFragmentManager(), data);
    ((ViewPager) findViewById(R.id.viewPager)).setAdapter(subGroupAdapter);
}

My viewpager adapter

public class SubAdapter extends FragmentPagerAdapter
{
    public SubGroupAdapter(FragmentManager fm, data data)
    {
        super(fm);
    }

@Override
public Fragment getItem(int position)
{
    Bundle bundle = new Bundle();
    bundle.putString("data", data);

    switch (position)
    {
        case 0:
            Fragment1 frag1 = new Fragment1();
            frag1.setArguments(bundle);
            return frag1;

        case 1:
            Fragment2 frag2 = new Fragment2();
            frag2.setArguments(bundle);
            return frag2;
    }

    return null;
}//some other methods below

Fragment1 / Fragment2 (both fragments have a listview)

public void onActivityCreated(Bundle savedInstanceState)
{
    super.onActivityCreated(savedInstanceState);

    frag1Adapter = new frag1Adapter(this, data);
    ((ListView) getView().findViewById(R.id.listView)).setAdapter(frag1Adapter);
}

Custom listview adapter for both listviews in both fragments

public class ExpenseAdapter extends BaseAdapter implements OnClickListener
{ ... }

As I mentioned earlier, I can input a new entry into either listview from the activity action bar button. However, the listview does not get updated and I can't reference the listview adapter to call notifydatasetchanged() from the activity.

What is the best way I can proceed from here onwards? thank you so much!

I have tried exploring using interfaces, tags but can't get it to work currently.

Answer 1

What you should do is create a public method for your Fragment1 and Fragment2 like so:

define in your Activity:

Fragment1 frag1; Fragment2 frag2;

then your ViewPager :

public class SubAdapter extends FragmentPagerAdapter
 {
    public SubGroupAdapter(FragmentManager fm, data data)
   {
      super(fm);
   }

 @Override
 public Fragment getItem(int position)
 {
    Bundle bundle = new Bundle();
    bundle.putString("data", data);

    switch (position)
    {
       case 0:
           frag1 = new Fragment1();
           frag1.setArguments(bundle);
           return frag1;

       case 1:
           frag2 = new Fragment2();
           frag2.setArguments(bundle);
           return frag2;
       }

     return null;
     }
}

Put this method in Fragment1.java :

public void updateFragment1ListView(){
   if(adapter != null){
       adapter.notifyDataSetChanged();
   }
}

and from your activity call:

  if(frag1 != null){
     frag1.updateFragment1ListView();
  }

obviously change the names for your adapter if its not called adapter...

Just do the same for Fragment2.java as well

Answer 2

I would recommend creating an interface. Here's an Example:

public interface UpdateListFragmentInterface {

    void updateList();
}

Then in the Activity, add the delegate as a property:

UpdateListFragmentInterface yourDelegate;

Wherever you create the Fragment within the Activity, assign the Fragment as the delegate:

// Set up and create your fragment.

(if yourFragment instanceof UpdateListFragmentInterface) {

    yourDelegate = yourFragment;
}

Then in the Fragment, implement the interface:

public class YourListFragment extends android.support.v4.app.ListFragment implements UpdateListFragmentInterface {

    // Constructors and other methods for the ListFragment up here.

    // Override the interface method
    public void updateList() {

        //Update the list here.
    }
}

Then finally, from within your Activity, when you need to update the list, simply call the delegate:

yourDelegate.updateList();

EDIT:

Sorry, I think you actually need to create a public method in your activity that is something like:

public void setUpdateListFragmentDelegate(UpdateListFragmentDelegate delegate) {

    this.delegate = delegate
}

Then in the on attach of the List Fragment you will assign it there:

if (context instance of YourActivity) {

    ((YourActivity)context.setUpdateListFragmentDelegate(this);
}