无法从 ViewPager Android Activity 动态添加或删除页面

Question

我已阅读有关此主题的所有 stackOverflow 答案，其中任何一个都对我有用，或者我自己无法做到。

正如您在下面的代码中看到的，我从 Android Studio 添加了默认的 ViewPager Activity，现在我需要从相应的按钮中添加新页面或删除现有页面。

因此，活动正确加载并获得正确数量的页面，并且我还可以成功更改每个页面中的信息。如您所见，该应用已连接到 Firebase，我从那里获得了我的活动应该拥有的页面（狗）总数，这运行良好。

现在，如何添加新页面、移动到该页面并更新适配器和页面总数？

删除也一样，如何删除当前页面，然后移动到另一个页面并更新适配器没有问题？

我对此感到非常疯狂，一整天都在使用我在 stackoverflow 中找到的不同解决方案，但无法做到。我现在对何时使用“notifyDataSetChanged()”感到困惑，是否覆盖“getItemPosition”是个好主意，等等。

如果有人最终可以帮助我将答案调整到我的项目，我将不胜感激，这是默认的 ViewPager 只是修改了小部分以尝试修复它，但不知道我还能做什么。

提前谢谢你，对不起我的英语。

注意：一些函数，如“updateIntValueFromCurrentUser()”在 MainActivity 中声明但可以工作，它们与 firebase 查询等有关，所以我不关注这个。

public class DummyViewPagerActivity extends MainActivity {

/**
 * The {@link android.support.v4.view.PagerAdapter} that will provide
 * fragments for each of the sections. We use a
 * {@link FragmentPagerAdapter} derivative, which will keep every
 * loaded fragment in memory. If this becomes too memory intensive, it
 * may be best to switch to a
 * {@link android.support.v4.app.FragmentStatePagerAdapter}.
 */
private SectionsPagerAdapter mSectionsPagerAdapter;

/**
 * The {@link ViewPager} that will host the section contents.
 */
private static ViewPager mViewPager;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_dummy_view_pager);

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    // Create the adapter that will return a fragment for each of the three
    // primary sections of the activity.
    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager) findViewById(R.id.container);
    mViewPager.setAdapter(mSectionsPagerAdapter);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });
}

//Creating menu bar
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_dummy_view_pager, menu);
    return true;
}
//Creating the two buttons to save and delete the images
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.

    switch (item.getItemId()) {
        case R.id.add:

            updateIntValueFromCurrentUser("dogs_number", person.getDogs_number()+1);
            return true;
        case R.id.edit:

            return true;
        case R.id.delete:

            updateIntValueFromCurrentUser("dogs_number", person.getDogs_number()-1);
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
}

/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {
    /**
     * The fragment argument representing the section number for this
     * fragment.
     */
    private static final String ARG_SECTION_NUMBER = "section_number";

    public PlaceholderFragment() {
    }

    /**
     * Returns a new instance of this fragment for the given section
     * number.
     */
    public static PlaceholderFragment newInstance(int sectionNumber) {
        PlaceholderFragment fragment = new PlaceholderFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, sectionNumber);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = null;
        try {
            rootView = inflater.inflate(R.layout.fragment_dummy_view_pager, container, false);
            TextView dogName = (TextView) rootView.findViewById(R.id.dog_name);
            dogName.setText(allDogs.get((getArguments().getInt(ARG_SECTION_NUMBER)) - 1).getName());
        } catch (Exception e) {
            Log.e("RaisedException()", e.getMessage());
        }
        return rootView;
    }
}

/**
 * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
 * one of the sections/tabs/pages.
 */
public class SectionsPagerAdapter extends FragmentStatePagerAdapter {

    public SectionsPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        // getItem is called to instantiate the fragment for the given page.
        // Return a PlaceholderFragment (defined as a static inner class below).
        return PlaceholderFragment.newInstance(position + 1);
    }

    @Override
    public int getItemPosition(Object object) {
    // POSITION_NONE makes it possible to reload the PagerAdapter
        return POSITION_NONE;
    }

    @Override
    public int getCount() {
        // Show x total pages.
            return person.getDogs_number();
    }

    @Override
    public CharSequence getPageTitle(int position) {
        switch (position) {
            case 0:
                return "SECTION 1";
            case 1:
                return "SECTION 2";
            case 2:
                return "SECTION 3";
        }
        return null;
    }
}

}

Answer 1

从 FragmentViewPager 添加/删除项目有点棘手：

尝试使用此适配器，让我知道它是否适合您。

public class CodebaseFragmentPagerAdapter extends FragmentStatePagerAdapter {

    private List<Fragment> mFragmentList = new ArrayList<Fragment>();

    public CodebaseFragmentPagerAdapter(FragmentManager manager) {
        super(manager);
    }

    @Override
    public Fragment getItem(int position) {
        return mFragmentList.get(position);
    }

    public void removeItem(int position){
        mFragmentList.remove(position == 0 ? 0 : position - 1);
        this.notifyDataSetChanged();
    }

    public void clearAllItems(){
        mFragmentList.clear();
        this.notifyDataSetChanged();
    }

    public void updateItem(int position, Fragment fragment){
        mFragmentList.set(position, fragment);
        notifyDataSetChanged();
    }

    @Override
    public int getItemPosition(Object object) {
        if (mFragmentList.contains(object)) return mFragmentList.indexOf(object);
        else return POSITION_NONE;
    }

    @Override
    public int getCount() {
        return mFragmentList.size();
    }

    public void addFrag(Fragment fragment) {
        mFragmentList.add(fragment);
        notifyDataSetChanged();
    }

}