如何使我的ViewPager一次只加载一个页面，即setOffscreenPageLimit(0)。

首先，复制SmartFragmentStatePagerAdapter.java，它在我们的ViewPager中提供了注册片段的智能缓存。它通过重写instantiateItem()方法和内部缓存任何创建的片段来实现。这解决了需要访问ViewPager中的当前项目的常见问题。

现在，在声明我们的适配器时，我们要从上面复制的SmartFragmentStatePagerAdapter扩展，这样我们就可以利用状态查询器的更好的内存管理。

public abstract class SmartFragmentStatePagerAdapter extends FragmentStatePagerAdapter {
    // Sparse array to keep track of registered fragments in memory
    private SparseArray<Fragment> registeredFragments = new SparseArray<Fragment>();
    public SmartFragmentStatePagerAdapter(FragmentManager fragmentManager) {
        super(fragmentManager);
    // Register the fragment when the item is instantiated
    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        Fragment fragment = (Fragment) super.instantiateItem(container, position);
        registeredFragments.put(position, fragment);
        return fragment;
    // Unregister when the item is inactive
    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        registeredFragments.remove(position);
        super.destroyItem(container, position, object);
    // Returns the fragment for the position (if instantiated)
    public Fragment getRegisteredFragment(int position) {
        return registeredFragments.get(position);
// Extend from SmartFragmentStatePagerAdapter now instead for more dynamic ViewPager items
    public static class MyPagerAdapter extends SmartFragmentStatePagerAdapter {
    private static int NUM_ITEMS = 3;
        public MyPagerAdapter(FragmentManager fragmentManager) {
            super(fragmentManager);
        // Returns total number of pages
        @Override
        public int getCount() {
            return NUM_ITEMS;
        // Returns the fragment to display for that page
        @Override
        public Fragment getItem(int position) {
            switch (position) {
            case 0: // Fragment # 0 - This will show FirstFragment
                return FirstFragment.newInstance(0, "Page # 1");
            case 1: // Fragment # 0 - This will show FirstFragment different title
                return FirstFragment.newInstance(1, "Page # 2");
            case 2: // Fragment # 1 - This will show SecondFragment
                return SecondFragment.newInstance(2, "Page # 3");
            default:
                return null;
        // Returns the page title for the top indicator
        @Override
        public CharSequence getPageTitle(int position) {
            return "Page " + position;