Question

好吧，伙计们，我的App有问题。我用一些片段创建了viewpager。这是我的观看者在我父母的活动中

   private int current_posisition_page ;

         @Override
            protected v

oid onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);

    .....
          viewpager.setAdapter(new PagePagerAdapter(getSupportFragmentManager()));
            viewpager.setCurrentItem(999);


            viewpager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {

                // This method will be invoked when a new page becomes selected.
                @Override
                public void onPageSelected(int position) {
                     current_posisition_page = position;
                }

                // This method will be invoked when the current page is scrolled
                @Override
                public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

                }


                @Override
                public void onPageScrollStateChanged(int state) {

                }
            });

    .......

    }

     private class PagePagerAdapter extends FragmentPagerAdapter {

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

            @Override
            public Fragment getItem(int pos) {
                return PageFragment.newInstance(pos);

            }

            @Override
            public int getCount() {
                return 1000;
            }

        }
    }

这是我的片段

public class PageFragment extends Fragment {

public static PageFragment newInstance(int page_index) {
        PageFragment fragment = new PageFragment();
        Bundle args = new Bundle();
        args.putString(Variabel.page_index, String.valueOf(page_index));
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            page_index = getArguments().getString(Variabel.page_index);
        }

        activity=(MainActivity)getActivity();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View v = inflater.inflate(R.layout.item_page, container, false);
        ButterKnife.bind(this, v);

        return v;
    }

  public void setSelectedAyat(String aya_id, String sura_name) {
        surat.setText("Surat " + sura_name);
        ayat.setText("Ayat " + aya_id);
}

}

现在我从父活动调用方法当前选定的片段viewpager：

PageFragment page = (PageFragment) adapter.getItem(current_posisition_page);
        page.setSelectedAyat(aya_id, sura_name);

但我收到错误：

java.lang.ClassCastException：java.lang.Integer无法强制转换为 com.ad.alquran.kemendag.fragment.PageFragment

排成一行：PageFragment page = (PageFragment) adapter.getItem(current_posisition_page);

那么如何解决呢？感谢

Answer 1

这一行可能导致问题：

viewpager.setAdapter(new PagePagerAdapter(getSupportFragmentManager()));

因为adapter对象用于调用getItem方法但在ViewPager setAdapter方法中传递PagePagerAdapter类的不同对象：

adapter=new PagePagerAdapter(getSupportFragmentManager());
viewpager.setAdapter(adapter);

并确保在为ViewPager设置适配器后调用getItem方法。

修改

java.lang.NullPointerException：尝试调用虚方法'void android.widget.TextView.setText（java.lang.CharSequence）'为null 对象参考

因为没有初始化surat和ayat。这样做：

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { // Inflate the layout for this fragment View v = inflater.inflate(R.layout.item_page, container, false); //... surat=(TextView)v. findViewById(R.id.<surat_id_in_xml>); ayat=(TextView)v. findViewById(R.id.<ayat_id_in_xml>); return v; }

从父活动调用方法当前选择的片段viewpager？

1 个答案: