从父活动访问选项卡式片段方法？

Question

Hi (I'm new to this so you'll have to forgive me)

I currently have a tabbed activity where MainActivity.java is the parent class and Absences.java and Notices.java are the fragments. I have a date picker fragment inside the MainActivity that is run when I tap on an options menu button.

When I've successfully selected my date I want to pass the information to a method in the Absences fragment. However, I'm really struggling with how to implement this part.

The research I've done seems to suggest this is the solution:

Absences fragment= (Absences) getSupportFragmentManager().findFragmentById(R.id.Absences);
        ((Absences)fragment).updateAbsences();

However, getSupportFragmentManager() can't be referenced from a static context and I can't seem to find the id of my Fragment.

After doing a little more research it seemed to reveal this method doesn't work for a tabbed activity so I'm at a loss at this point.

Would someone be able to point me in the right direction? - I've been working on this for quite some time now!

SectionsPageAdapter class

Fragment one, two;

public class SectionsPagerAdapter extends FragmentPagerAdapter {

    public SectionsPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        // getItem is called to instantiate the fragment for the given page.
        // Return a PlaceholderFragment (defined as a static inner class below).
        switch (position) {
            case 0:
                if(one==null){
                    one = new Absences();
                }
                return one;
            case 1:
                if(two==null){
                    two = new Notices();
                }
                return two;
        }
        return null;
    }

    @Override
    public int getCount() {
        // Show 3 total pages.
        return 2;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        switch (position) {
            case 0:
                return "ABSENCES";
            case 1:
                return "NOTICES";
        }
        return null;
    }

}

onOptionsItemSelected

 public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();
    if (id == R.id.calendar) {
        DialogFragment newFragment = new DatePickerFragment();
        newFragment.show(getSupportFragmentManager(), "datePicker");
    }
    return super.onOptionsItemSelected(item);
}

DatePickerFragment

public static class DatePickerFragment extends DialogFragment
        implements DatePickerDialog.OnDateSetListener {

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        final Calendar c = Calendar.getInstance();
        int year = c.get(Calendar.YEAR);
        int month = c.get(Calendar.MONTH);
        int day = c.get(Calendar.DAY_OF_MONTH);
        DatePickerDialog dialog = new DatePickerDialog(getActivity(), this, year, month, day);
        dialog.getDatePicker().setMaxDate(c.getTimeInMillis());
        dialog.setTitle("");
        return  dialog;
    }

    public void onDateSet(DatePicker view, int year, int month, int day) {
        Absences fragment= (Absences) getSupportFragmentManager().findFragmentById(R.id.Absences);
        ((Absences)fragment).updateAbsences();
    }
}

--EDIT--

Updated code as per suggestion below

Method inside MainActivity

public void onDatePicked() {
    Absences fragment = (Absences) getSupportFragmentManager().findFragmentById(R.id.absences);
    fragment.updateAbsences();
}

New DatePickerFragment Class

    package com.alexwoohouse.heartofengland;

import android.annotation.TargetApi;
import android.app.DatePickerDialog;
import android.app.Dialog;
import android.icu.util.Calendar;
import android.os.Build;
import android.os.Bundle;
import android.support.v4.app.DialogFragment;
import android.util.Log;
import android.widget.DatePicker;

import java.util.Date;

public class DatePickerFragment extends DialogFragment
        implements DatePickerDialog.OnDateSetListener {

    public interface OnDatePickedListener {
        void onDatePicked(); //This method seems to be greyed out!
    }

    @TargetApi(Build.VERSION_CODES.N)
    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        final Calendar c = Calendar.getInstance();
        int year = c.get(Calendar.YEAR);
        int month = c.get(Calendar.MONTH);
        int day = c.get(Calendar.DAY_OF_MONTH);
        DatePickerDialog dialog = new DatePickerDialog(getActivity(), this, year, month, day);
        dialog.getDatePicker().setMaxDate(c.getTimeInMillis());
        dialog.setTitle("");
        return  dialog;
    }

    @TargetApi(Build.VERSION_CODES.N)
    public void onDateSet(DatePicker view, int year, int month, int day) {
        Calendar cal = Calendar.getInstance();
        cal.set(Calendar.YEAR, year);
        cal.set(Calendar.MONTH, month);
        cal.set(Calendar.DAY_OF_MONTH, day);
    }
}

Answer 1

Here's my suggestion.

First, move DatePickerFragment out as its own top-level class. I don't know if you have a good reason for having it be a static inner class, but you likely don't need that.

Now then, generally the way you have fragments (dialog or otherwise) pass information is via interface callbacks. So instead of trying directly access the current activity's fragment manager as your are doing, you invoke a callback with the data you have to send. See the android documentation on this for details and sample code, but basically you'd define an interface in your DatePickerFragment that will be invoked when a date is picked:

public interface OnDatePickedListener {
    void onDatePicked(Date date);
}

When your fragment is attached to the activity, you save that as the fragment's current listener instance. When you pick a date in the dialog fragment, you invoke your listener's onDatePicked method.

Your activity then implements this interface to delegate down to the fragment you want to update:

public class MainActivity implements DatePickerFragment.OnDatePickedListner {
    @Override
    public void onDatePicked(Date date) {
        Absences fragment = (Absences) getSupportFragmentManager().findFragmentById(R.id.Absences);
        fragment.updateAbsences();
    }
}

The main benefit to this being separation of concerns. Your dialog fragment does not know anything about the Activity that owns it. It just knows that it has to report the selected date to whomever implements the interface. Then you can show this dialog fragment in any other Activity you need to pick a date in as long as they also implement the correct interface.

Hope that helps!