Question

我正在阅读有关片段的View Paging的Android开发人员指南，并坚持从我的主onCreate方法填充片段。我觉得我很困惑在填充片段时调用哪些方法，因为我得到空值。

My Fragment Class

public class CatalogFragment extends Fragment {
    private String filename;
    private String author;
    private String title;

    public CatalogFragment(String f, String t, String a){
        filename = f;
        author = a;
        title = t;
        Log.d("frag", f+" | "+t+" | "+a);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
        ViewGroup rootView = (ViewGroup) inflater.inflate(R.layout.catalog_fragment,  container, false);
        ImageView imgView = (ImageView) rootView.findViewById(R.id.imgFrag);
        Bitmap bmp = BitmapFactory.decodeFile(filename);
        imgView.setImageBitmap(bmp);
        TextView txtView = (TextView)rootView.findViewById(R.id.title_text);
        txtView.setText(author+": "+title);
        return rootView;
    }
}

我的onCreate

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

    //Instantiate a ViewPager and a PagerAdapter
    mPager = (ViewPager) findViewById(R.id.pager);
    mPagerAdapter = new ScreenSlidePagerAdapter(getSupportFragmentManager());
    mPager.setAdapter(mPagerAdapter);

    //populate the fragment
    //I was thinking I could pass the fragment class the necessary information to put an imageview and text view in place.

    List<Poster> posters = db.getAllPosters();
    for (Poster p : posters) {
        final String filename = p.getPosterFilename();

    //Create a new Fragment?
        new CatalogFragment(filename, p.getPosterTitle(), p.getPresenterFname()+" "+p.getPresenterLname());

    }

}

然而，似乎getItem实际上被调用来填充片段。我认为。如果我把null放入我得到的参数中。如果我试图省略这一行，eclipse开始抱怨。所以我被卡住了。

private class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter{

        public ScreenSlidePagerAdapter(FragmentManager fm) {
            super(fm);
            // TODO Auto-generated constructor stub
        }

        @Override
        public Fragment getItem(int position){
            return new CatalogFragment(null, null, null);
        }

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

    }

Answer 1

适配器是在视图寻呼机中创建片段的原因，您无需自己创建它们。

以下是Adapter和Activity＃onCreate可能为您提供正确结果的内容。

注意我们如何告诉适配器从哪里获取数据。

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

    //Instantiate a ViewPager and a PagerAdapter
    mPager = (ViewPager) findViewById(R.id.pager);

    mPagerAdapter = new ScreenSlidePagerAdapter(getSupportFragmentManager());
    mPagetAdapter.setData(db.getAllPosters()); // Provide Poster Data to Adapter
    mPager.setAdapter(mPagerAdapter);
}

在适配器中，我们告诉它如何构建它的片段：

private class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter {
    List<Poster> posterList = new ArrayList<Poster>(0);
    public ScreenSlidePagerAdapter(FragmentManager fm) {
        super(fm);
        // TODO Auto-generated constructor stub
    }

    public void setData(List<Poster> posters) {
        posterList.addAll(posters);
    }

    @Override
    public Fragment getItem(int position){
        Poster poster = posterList.get(position)
        // FRAGMENTS SHOULD NOT IMPLEMENT A CONTRUCTOR!!!
        // This will lead to other issue down the line.
        return new CatalogFragment(poster.getPosterFilename(), poster.getPosterTitle(), poster.getPresenterFname()+" "+poster.getPresenterLname());
    }

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

}

```

作为旁注，你不应该有一个带参数的片段构造函数。请参阅此其他SO问题以获得解释：Do fragments really need an empty constructor?

以编程方式创建和填充viewpager片段。结果为空

1 个答案: