I would like to keep a list of 3 views at all times. The app starts at position 1 (out of positions 0,1,2). When someone scrolls to position 0, I would like to remove view 2, and create a view before position 0. This way, it appears to the user, that there are unlimited views. In the same way, when someone scrolls to position 2, I would like to remove the view at position 0 and add one at the end.
However I'm having problems with both adding and removing views. When I get to position 0, nothing changes unless I try scrolling past position 0 (to position -1, i.e. the boundary is hit). At that point, I can see that it is the boundary of my views, but then setCurrentItem(1,false) is triggered and I'm brought back to the middle of the views. When I scroll to position 2 I see that position 2 has been updated. However position 0 and 1 remain the same.
When I scroll to position 2, nothing happens. However if I try and scroll to the boundary, for some reason, position 0 gets updated and setCurrentItem(1,false) is triggered.
I have no idea why its happening like this. Can anyone shed some light on this?
Here is my code:
public class MainActivity extends Activity {
ArrayList<Integer> showThree = new ArrayList<Integer>();
int focusedPage = 0;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
showThree.add(0,5); //adding integers 5,6,7 for positions 0,1,2
showThree.add(1,6);
showThree.add(2,7);
final MyPagerAdapter adapter = new MyPagerAdapter(getApplicationContext(),showThree);
final ViewPager myPager = (ViewPager) findViewById(R.id.mypanelpager);
myPager.setAdapter(adapter);
myPager.setCurrentItem(1);
myPager.setOnPageChangeListener(new OnPageChangeListener(){
@Override
public void onPageScrollStateChanged(int state) {
if (state == ViewPager.SCROLL_STATE_IDLE) {
//when position= 0, change the 3 views from 5,6,7 to 4,5,6.
if (focusedPage == 0) {
showThreeMonths.set(0,4);
showThreeMonths.set(1,5);
showThreeMonths.set(2,6);
adapter.notifyDataSetChanged();
adapter.startUpdate(myPager);
}
else if (focusedPage ==2){
//ignore, just testing focusPage=0 for now }
}
//set current page to the middle of the 3 new views, which would be
//the same view at position 0 of the old 3 views.
//Thus user doesn't experience the views changing despite being 3 new views.
myPager.setCurrentItem(1,false);
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
// TODO Auto-generated method stub
}
@Override
public void onPageSelected(int position) {
focusedPage = position;
}
});
}
PagerAdapter
public class MyPagerAdapter extends PagerAdapter {
private ArrayList<Integer> showThreeMonths;
private Context ctx;
public MyPagerAdapter (Context ctx, ArrayList<Integer> showThree){
this.ctx = ctx ;
this.showThree = showThree;
}
@Override
public int getCount() {
return showThree.size();
}
public Object instantiateItem(ViewGroup collection, int position ){
//NewCustomView is a class I made that takes parameters context and an integer and creates a view based on the integer
NewCustomView MyOwnView = new NewCustomView(ctx, showThree.get(position));
View customViewLayout = MyOwnView.newLayout; //part of the class object
collection.addView(customViewLayout);
return customViewLayout;
}
@Override
public void destroyItem(ViewGroup collection, int position, Object arg2) {
((ViewPager) collection).removeView((ViewGroup) arg2);}
@Override
public Parcelable saveState() {
return null;}
@Override
public boolean isViewFromObject(View view, Object arg1) {
return view==arg1;}
@Override
public void startUpdate(ViewGroup collection) {}
@Override
public void finishUpdate(ViewGroup collection) {}
}
