Android中的片段和ViewPager

Question

I am having a ViewPager to allow the user to slide between 5 different views where each "view" extends Fragment.

I have my own adapter which extend FragmentPagerAdapter and which implement getItem() as

@Override public Fragment getItem(int position) {
   switch(position) {
      case 0: 
          return new TextDescriptionFragment();
      // Handle the 4 other cases the same way
   }
}

This works fine and the user can swipe between the 5 different views. But here comes the problem: Each of the first 4 views contains Views such as Button and EditText which the user can interact with.

And I then want the last page(Page number 5) to show all the user input values from all the views from the 4 previous pages(fragments). How do I do that?

I can't find any way to read the user input values from the previous fragments. The views may not even exist anymore(But will be recreated if the user goes back).

And I can't seem to get the existing fragments.

Answer 1

I would consider having a custom object that keeps the data each fragment fills. Something like:

public class FillerData implements Parcelable {
    private String page0$data0;
    private String page0$data1;
    private String page0$data2;

    // getters and setters if you wish

    // implement Parcelable interface as this object will be managed by host activity
}

You'll have only one such object managed by parent activity and the parent activity will implement an interface for exposing this object:

public static interface FillerDataExposer {
    public FillerData exposeFiller();
}

public class MyFragmentHostActivity extends FragmentActivity implements FillerDataExposer {
    private static final String FILLER_KEY = "FILLER_KEY";
    private FillerData myFillerData;

    protected void onCreate(Bundle savedInstance) {
        .......
        if(savedInstance != null) {
            myFillerData = (FillerData) savedInstance.getParcelable(FILLER_KEY);
        } else {
            myFillerData = new FillerData();
        }
    }

    protected void onSaveInstanceState(Bundle savedInstance) {
        super.onSaveInstanceState();
        savedInstance.putExtra(FILLER_KEY, myFillerData);
    }

    public FillerData exposeFiller() {
        return this.myFillerData;
    }
}

Now, each of your fragments will have access to that centralized data filler object through parent activity. To reduce the weight of your code, all your fragments could extend from a base fragment class that provides access to FillerDataExposer implementation (actually, the parent activity):

public abstract class AbstractFillerFragment extends Fragment {
    protected FillerDataExposer dataExposer;

    public void onAttach(Activity act) {
        super.onAttach(act);
        // make sure no ClassCastExceptions
        this.dataExposer = (FillerDataExposer) act;
    }
}

Fragments that should only record the data filled could look like this:

public class Page1Fragment extends AbstractFillerFragment {

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = // inflate XML resource ...
        yourEditText = (EditText) view.findViewById(...);
        // other relevant code ....
    }

    public void onViewCreated(View view, Bundle savedInstanceState) {
       yourEditText.setText(dataExposer.exposeFiller.setPageX$DataY());
       // some code for EditText.addTextChangedListener(new TextWatcher() could look like:
        yourEditText.addTextChangedListener(new TextWatcher() {

          public void afterTextChanged(Editable s) {

            dataExposer.exposeFiller().setPage1$Data0(s.toString());

          }

          public void beforeTextChanged(CharSequence s, int start, int count, int after) {}

          public void onTextChanged(CharSequence s, int start, int before, int count) {}
       });
    }
}

While the fragment that needs to have access to all data stored could look like this:

public class FinalFragment extends AbstractFillerFragment {
    public void collectAllData() {
        DataFiller allDataCollectedObject = dataExposer.exposeFiller();
        // by calling get...() you should have access to collected data.
    }
}

This only a sketch, but you'll get the picture. The idea is to keep a single object in your activity managed across activity restarts and to make it accessible through interfaces so you will respect the fragment to activity patterns.

Hope it makes sense ...

Answer 2

2 solutions come to my mind.

The first one is to save user input data when your first 4 fragment's onpause() methods are called. You may save the data to a preference and then retrieve it from your 5th fragment.

The second approach is to persist your fragments while swiping.This way the swiping will be faster and cleaner and they want be recreated everytime a swipe happens:

yourcustomviewpager.setOffscreenPageLimit(5);

About setOffscreenPageLimit from the android doc :

Set the number of pages that should be retained to either side of the current page in the view hierarchy in an idle state. Pages beyond this limit will be recreated from the adapter when needed. This is offered as an optimization. If you know in advance the number of pages you will need to support or have lazy-loading mechanisms in place on your pages, tweaking this setting can have benefits in perceived smoothness of paging animations and interaction. If you have a small number of pages (3-4) that you can keep active all at once, less time will be spent in layout for newly created view subtrees as the user pages back and forth. You should keep this limit low, especially if your pages have complex layouts. This setting defaults to 1.