Calendar and PagerAdapter - Unlimited Views

问题

In my activity, I'm using ViewPager to swipe left/right and show month view accordingly. I'm passing the month and year values from onCreate to the PagerAdapter:

private static int NUM_AWESOME_VIEWS = 3;

viewPager = (ViewPager) v.findViewById(R.id.pager);
cAdapter = new CalendarPagerAdapter(this.getActivity().getApplicationContext(), date_value, fragmentManager, month, year);
viewPager.setAdapter(cAdapter);
viewPager.setOffscreenPageLimit(3);

The Calendar starts from November and then scrolls till January. I would like the Calendar to display unlimited views forward and backward.

PagerAdapter:

public CalendarPagerAdapter(Context context, int dv, FragmentManager fm, int month, int year){
    this.context = context;
    this.dv = dv;
    this.fm = fm;
    this.month = month;
    this.year = year;

}

public Object instantiateItem(View collection, int position) {
    Log.d("Object", "Instantiated");
    LayoutInflater inflater = (LayoutInflater) collection.getContext()
                     .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

    View v =  inflater.inflate(R.layout.simple_calendar_view, null);

    _calendar.set(Calendar.MONTH, month);
    _calendar.set(Calendar.YEAR, year);

    month = _calendar.get(Calendar.MONTH) + 1;
    year = _calendar.get(Calendar.YEAR);

    currentMonth = (Button) v.findViewById(R.id.currentMonth);
    currentMonth.setText(hijri.getMonthForInt(month-1).toUpperCase() + " " + year);

    calendarView = (GridView) v.findViewById(R.id.calendar);
    calendarWeek = (GridView) v.findViewById(R.id.calendarweek);

    calendarWeek.setAdapter(new CalendarWeekAdapter(context, firstDay));
    // Initialised
    adapter = new GridCellAdapter(calendarView, context, R.id.calendar_day_gridcell, month, year, 0, 0, 0);
    adapter.notifyDataSetChanged();
    calendarView.setAdapter(adapter);

    ((ViewPager) collection).addView(v, 0);

    return v;
}

Based on Jon Willis' code, this is what I have come up with, but when the position of the viewpager is 0 or 2, the page goes blank and then displays the next month + 1 (that is, after I scroll January, the page flickers and displays March). It does not scroll smoothly. I am not sure how else to do it.

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

    }

    @Override
    public void onPageScrollStateChanged(int state) {
            if (state == ViewPager.SCROLL_STATE_IDLE) 

                 Log.d("Calendar ViewPager", "Calendar ViewPager" + viewPager.getCurrentItem());

                    if (focusedPage == 0) {

                            _calendar.add(Calendar.MONTH, -1);
                            month = _calendar.get(Calendar.MONTH);
                            year = _calendar.get(Calendar.YEAR);

                            setGridCellAdapter(context, month, year);

                    } else if (focusedPage == 2) {

                           _calendar.add(Calendar.MONTH, +1);
                           month = _calendar.get(Calendar.MONTH);
                           year = _calendar.get(Calendar.YEAR);


                           setGridCellAdapter(context, month, year);

                    }

                    viewPager.setCurrentItem(1, false);
            }
    }

    @Override
    public void onPageSelected(int position) {
            focusedPage = position;
    }
});



public void setGridCellAdapter(Context ctx, int month, int year)
{
    cAdapter = new CalendarPagerAdapter(ctx, date_value, fragmentManager, month, year);
    Log.d("Object", "Re-instantiatted" + month + year);
    cAdapter.notifyDataSetChanged();
    viewPager.setAdapter(cAdapter);

}

回答1:

I have achieve to implement this but not perfectly by using each page as 3 fragments. When User swift right or left, It will set back to middle and update new data source for each fragment.

In Main

MonthViewContentFragment[] fragList = new MonthViewContentFragment[3];
fragList[0] = MonthViewContentFragment.newInstance(prevMonth);
fragList[1] = MonthViewContentFragment.newInstance(currentMonth);
fragList[2] = MonthViewContentFragment.newInstance(nextMonth);

ViewPager monthPage = (ViewPager) v.findViewById(R.id.monthview_content);
MonthPageAdapter monthPageAdapter = new MonthPageAdapter(getFragmentManager(), fragList);
monthPage.setAdapter(monthPageAdapter);
monthPage.setOnPageChangeListener(this);
monthPage.setCurrentItem(1, false);

in onPageScrollStateChanged

if (state == ViewPager.SCROLL_STATE_IDLE) {

    if (focusPage < PAGE_CENTER) {
        currentMonth.add(Calendar.MONTH, -1);
    } else if (focusPage > PAGE_CENTER) {
        currentMonth.add(Calendar.MONTH, 1);    
    }
    monthPageAdapter.setCalendar(currentMonth);
    monthPage.setCurrentItem(1, false);
    updateTitle();
}

in onPageSelected

public void onPageSelected(int position) {
        // TODO Auto-generated method stub
        focusPage = position;
}

In MonthPageAdapter

    MonthViewContentFragment[] fragList;    
    MonthViewContentFragment temp; 
    int fragNumber = 3;

    public MonthPageAdapter(FragmentManager fm, MonthViewContentFragment[] fragList) {
        super(fm);
        this.fragList = fragList;
    }

    @Override
    public int getItemPosition(Object object) {
        // TODO Auto-generated method stub
        return POSITION_NONE;
    }
    @Override
    public Fragment getItem(int position) {
        return fragList[position];      
    }

    @Override
    public int getCount() {
        return 3;
    }
    public void setCalendar(Calendar currentMonth) {

        Calendar prevMonth = Calendar.getInstance();
        prevMonth.setTime(currentMonth.getTime());
        prevMonth.add(Calendar.MONTH, -1);

        Calendar nextMonth = Calendar.getInstance();
        nextMonth.setTime(currentMonth.getTime());
        nextMonth.add(Calendar.MONTH, 1);
            //update all 3 fragments
        fragList[0].updateUI(prevMonth);
        fragList[1].updateUI(currentMonth);
        fragList[2].updateUI(nextMonth);
    }

In MonthViewContentFragment

    @Override
    public void updateUI(Calendar monthYear) {

        View v = getView();
        if (v == null)
            return;
        //setNewDataSource calcurate new List<String> date
        calendarViewAdapter.setNewDataSource(monthYear);
        calendarViewAdapter.notifyDataSetChanged();
    }

This is not perfect because when user swift too fast. The scroll is not change to idle yet then ViewPager reach its end.

回答2:

I'm not sure i understand this (never used this viewPager, have always used another HorizontalViewSlider instead), but for your onPageScrollStateChanged() why do you have a special case for focusedPage==0 and focusedPage==2 ?

if nothing is special about Jan and March, maybe remove everything inside onPageScrollStateChanged() ?

my guess is that the flickering is from when you call setGridCellAdapter() because that will refresh the page from calling notifyDataSetChanged.

来源：https://stackoverflow.com/questions/13218434/calendar-and-pageradapter-unlimited-views