Updating a TextView in a ViewPager Fragment

Question

In my Android app, I'm having trouble setting a TextView that is located in a fragment from the parent activity. I am using a ViewPager as follows:

In my main activity's onCreate():

List<Fragment> fragments = new Vector<Fragment>();
fragments.add(Fragment.instantiate(this, MainPageProfileFragment.class.getName()));
fragments.add(Fragment.instantiate(this, MainPageOtherFragment.class.getName()));
mainPagerAdapter = new ViewPagerAdapter(this.getSupportFragmentManager(), fragments);
ViewPager pager = (ViewPager)findViewById(R.id.viewpager);
pager.setAdapter(mainPagerAdapter);

with the ViewPagerAdapter:

public class ViewPagerAdapter extends FragmentPagerAdapter{
    private List<Fragment> fragments;
    public ViewPagerAdapter(FragmentManager fm, List<Fragment> fragments) {
        super (fm);
        this.fragments = fragments;
    }
    @Override
    public Fragment getItem(int arg0) {
        return this.fragments.get(arg0);
    }
}

And the MainPageProfileFragment below. This fragment provides an interface to update a TextView at runtime (after the view is created).

public class MainPageProfileFragment extends Fragment
    implements View.OnClickListener {
    private TextView profileImageLabelTextView;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
        if(container == null) {
            return null;
        }
        ScrollView view = (ScrollView)inflater.inflate(R.layout.fragment_main_page_profile, container, false);
        labelTextView = (TextView) view.findViewById(R.id.profileLabel);
        return view;
    }
    public void setLabelText(String text) {
        labelTextView.setText(text);
    }
}

The setLabelTextView() I'd like to call from the main activity's onResume() handler, but I haven't yet been able to get a handle on the fragment that would allow me to access this method. I'm going a bit in circles now as I have found different approaches for accessing views in fragments where this seemed to be the most plausible but I haven't succeeded yet. How would I call the setLabelText() method from my activity?

@Override
protected void onResume() {
    super.onResume();
    // set the labelTextView here
}

Answer 1

The straitforward way would be to lookup ViewPager , then take ViewPagerAdapter and then try to get the fragment. If fragment is there, you can call setLabelText() method. Something like this.

@Override
protected void onResume() {
    super.onResume();

    ViewPager pager = (ViewPager)findViewById(R.id.viewpager);
    ViewPagerAdapter adapter = (ViewPagerAdapter) pager.getAdapter();
    Fragment fragment = adapter.getItem(0);
    if (fragment instanceof MainPageProfileFragment) {
        // if we are here, then fragment is not null and has correct type
        ((MainPageProfileFragment)fragment).setLabelText("my text");
    }
}

To add getItem() method to an Adapter , you should extend FragmentPagerAdapter and track list of Fragments by your own. Like this

public class PagerAdapter extends FragmentPagerAdapter {

    private List<Fragment> mFragments = new ArrayList<Fragment>();

    @Override
    public Fragment getItem(int position) {
        return mFragments.get(position);
    }

    @Override
    public int getCount() {
        return mFragments.size();
    }

    public void addFragment(Fragment fragment) {
        mFragments.add(fragment);
        notifyDataSetChanged();
    }
}

But a more elegant and flexible solution would be to use a event bus for Activity to Fragment communication. There are some event buses implementation out there. You can try TinyBus or EventBus .

Answer 2

我不认为这是最好的解决方案，但你可以尝试使用内部名称按标签名称检索片段：

"android:switcher:" + viewId + ":" + index;

Answer 3

Try this

viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                ViewPagerAdapter adapter = (ViewPagerAdapter) viewPager.getAdapter();
                Fragment fragment = adapter.getItem(position);
                if (fragment instanceof BiographyFragment) {
                    // if we are here, then fragment is not null and has correct type
                    if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.N) {
                        ((BiographyFragment) fragment).mTextViewBiography.setText(fromHtml(mBiography, Html.FROM_HTML_MODE_LEGACY));
                    } else {
                        ((BiographyFragment) fragment).mTextViewBiography.setText(fromHtml(mBiography));
                    }
                }
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });