Smooth scroll does not work in ViewPager (support

问题:

I am writing application that uses ViewPager to host Fragments.

When I change fragment programmatically the smooth scroll function does not work. I use ViewPager.setCurrentItem(int item, boolean smoothScroll)` method.

Maybe anyone know a workaround this bug? Maybe with animations?

EDIT: I am using support package. And the issue is that whether I use ViewPager.setCurrentItem(2, true) or ViewPager.setCurrentItem(2, false) the result is the same. The view switches really fast (not smoothly).

回答1:

I've fixed this by creating a MyViewPager that overrides the ViewPager.mScroller using reflection.

public class MyViewPager extends ViewPager 
{
  public MyViewPager( Context context, AttributeSet attrs) 
  {
    super( context, attrs );
    setMyScroller();
  }
  private void setMyScroller() 
  {
    try 
    {
            Class<?> viewpager = ViewPager.class;
            Field scroller = viewpager.getDeclaredField("mScroller");
            scroller.setAccessible(true);
            scroller.set(this, new MyScroller(getContext()));
    } catch (Exception e) 
    {
        e.printStackTrace();
    }
  }

  public class MyScroller extends Scroller 
  {
    public MyScroller(Context context) 
    {
        super(context, new DecelerateInterpolator());
    }

    @Override
    public void startScroll(int startX, int startY, int dx, int dy, int duration) 
    {
        super.startScroll(startX, startY, dx, dy, 1000 /*1 secs*/);
    }
  }
} 

回答2:

What worked for me was to call mPager.setCurrentItem after the mPagerAdapter.notifyDataSetChanged(), and not as a posted runnable.

Here is an example (in MonoDroid):

    public void UpdateDetialsView(string type)
    {
        string typeName4 = Java.Lang.Class.FromType(typeof(ParcelRecordComplaintDetailsView)).Name;

        if (_fragments.Count > 3)
        {
            _fragments.RemoveAt(_fragments.Count - 1);

            ////////////////////////////////////////////////////////////
            // Called here it wasn't working for me (Posted or not)

            //_viewPager.Post(new Action(() => { _viewPager.SetCurrentItem(3, true); }));
        }

        _fragments.Add(Fragment.Instantiate(Activity, typeName4));

        _pagerAdapter.NotifyDataSetChanged();

        ////////////////////////////////////////////////////////////
        // Called here it works as expected

        _viewPager.SetCurrentItem(3, true);
    }

where

    protected MyAdapter _pagerAdapter;
    protected ViewPager _viewPager;
    private List<Android.App.Fragment> _fragments;

and

    public class MyAdapter : Android.Support.V13.App.FragmentStatePagerAdapter
    {
        private List<Fragment> _fragments;

        public override Java.Lang.Object InstantiateItem(View p0, int p1)
        {
            return base.InstantiateItem(p0, p1);
        }

        public MyAdapter(Android.App.FragmentManager fm) : base(fm)
        {

        }

        public MyAdapter(Android.App.FragmentManager fm, List<Android.App.Fragment> fragments) : base(fm)
        {
            _fragments = fragments;
        }

        public override int Count
        {
            //get { return FRAG_PAGES; }
            get { return _fragments.Count; }
        }

        public override Android.App.Fragment GetItem(int p0)
        {
            return _fragments[p0];
        }

        public override float GetPageWidth(int p0)
        {
            //return base.GetPageWidth(p0);

            return (float) (0.5f);
        }

        public override int GetItemPosition(Java.Lang.Object p0)
        {
            //return base.GetItemPosition(p0);
            return PagerAdapter.PositionNone;
        }
    }