android - PagerAdapter 类被多次调用

Question

我正在开发一个包含 ViewPager View 的应用程序， 我创建了一个 PagerAdapter，它具有 View ，PagerAdapter 的 instantiateItem() 方法在 create() 中被调用了两次 我不知道为什么，有人可以帮我解决这个问题吗？

这是我的代码，

         View PagerView;
        MyPagerAdapter adapter;
        ViewPager pager;

            adapter = new MyPagerAdapter();     
    pager.setAdapter(adapter);
    pager.setCurrentItem(0);

public class MyPagerAdapter extends PagerAdapter {

        @Override
        public Object instantiateItem(final View collection, final int position) {
            Log.d("Inside", "Pager");
            PagerView = new View(collection.getContext());
            LayoutInflater inflater = (LayoutInflater) collection.getContext()
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            PagerView = inflater.inflate(R.layout.tablemenu, null, false);
            tbMenuDetails = (TableLayout) PagerView
                    .findViewById(R.id.Menutable1);
            scrollview = (ScrollView) PagerView.findViewById(R.id.scrollView1);
            tbMenuDetails.removeAllViews();
            removeTableRows();
            createTableLayout(position);
            String str[][] = datasource.GetSubMenuDetailsFromMenuId(MenuIdlst
                    .get(position).trim());
            Log.d("Str", "" + str.length);
            for (int i = 0; i < str.length; i++) {
                addRows(str[i][1], str[i][2], str[i][0], str[i][3], position);
                Log.d("Message", "Pos   " + position + "    SubMenuName" + str[i][2]
                        + " SubMenuId" + " " + str[i][0] + " TypeID" + "    "
                        + str[i][3]);
            }

            // View view = inflater.inflate(resId, null);
            ((ViewPager) collection).addView(PagerView, 0);

            return PagerView;
        }

        @Override
        public void destroyItem(final View arg0, final int arg1,
                final Object arg2) {
            ((ViewPager) arg0).removeView((View) arg2);

        }

        @Override
        public boolean isViewFromObject(final View arg0, final Object arg1) {
            return arg0 == ((View) arg1);

        }

        @Override
        public void finishUpdate(View arg0) {
            // TODO Auto-generated method stub

        }

        @Override
        public void restoreState(Parcelable arg0, ClassLoader arg1) {
            // TODO Auto-generated method stub

        }

        @Override
        public Parcelable saveState() {
            // TODO Auto-generated method stub
            return null;
        }

        @Override
        public void startUpdate(View arg0) {
            // TODO Auto-generated method stub

        }

        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return MenuIdlst.size();
        }

    }

请帮忙

Answer 1

如果您决定使用 Fragment，请不要实现 PagerAdapter。相反，扩展 FragmentPagerAdapter 或 FragmentStatePagerAdapter:

private class MyPagerAdapter extends FragmentStatePagerAdapter {
    public MyPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public int getCount() {
        return NUMBER_OF_PAGES_IN_PAGER;
    }

    @Override
    public Fragment getItem(int position) {
        // Implement the static method newInstance in MyFragment.java yourself.
        // It should return you a brand new instance of MyFragment, basically using
        // the code you had in your original instantiateItem method.
        return MyFragment.newInstance(position, ... etc ...); 
    }
}

然后在您的 Activity 中:

myPagerAdapter = new MyPagerAdapter(getFragmentManager());
// or myPagerAdapter = new MyPagerAdapter(getSupportFragmentManager());
myViewPager.setAdapter(myPagerAdapter);

要获得有关如何使用 Fragments 和 ViewPagers 的更多信息: https://developer.android.com/reference/android/app/Fragment.html https://developer.android.com/reference/android/support/v4/view/ViewPager.html https://developer.android.com/reference/android/support/v4/app/FragmentStatePagerAdapter.html