Android在FragmentPagerAdapter中的Fragment中设置TextView文本

这个让我疯了.基本上,我想创建一个ViewPager并为其添加一些片段.然后,我想做的就是在Fragment的TextViews中设置一个值.我可以添加Fragments,并且它们会附加,但是当我在第一个Fragment中找到其中一个TextViews的findViewById()时,它会抛出一个NullPointerException.我,为了我的生活,无法弄清楚为什么.

到目前为止,这是我的代码,请告诉我是否需要更多代码.

public class SheetActivity extends FragmentActivity {

    // /////////////////////////////////////////////////////////////////////////
    // Variable Declaration
    // /////////////////////////////////////////////////////////////////////////
    private ViewPager               viewPager;
    private PagerTitleStrip         titleStrip;
    private String                  type;
    private FragmentPagerAdapter    fragmentPager;  //UPDATE

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

        viewPager = (ViewPager) findViewById(R.id.viewPager);
        titleStrip = (PagerTitleStrip) findViewById(R.id.viewPagerTitleStrip);

        // Determine which type of sheet to create
        Intent intent = getIntent();
        this.type = intent.getStringExtra("type");
        FragmentManager manager = getSupportFragmentManager();
        switch (type) {
            case "1":
                viewPager.setAdapter(new InstallAdapter(manager));
                break;
            case "2":
                viewPager.setAdapter(new InstallAdapter(manager));
                break;
        }
        fragmentPager = (FragmentPagerAdapter) viewPager.getAdapter();  //UPDATE
    }

    @Override
    public void onResume() {
        super.onResume();

        fragmentPager.getItem(0).setText("something"); //UPDATE
    }

    class MyAdapter extends FragmentPagerAdapter {

        private final String[]      TITLES      = { "Title1","Title2" };
        private final int           PAGE_COUNT  = TITLES.length;
        private ArrayList<Fragment> FRAGMENTS   = null;

        public MyAdapter(FragmentManager fm) {
            super(fm);
            FRAGMENTS = new ArrayList<Fragment>();
            FRAGMENTS.add(new FragmentA());
            FRAGMENTS.add(new FragmentB());
        }

        @Override
        public Fragment getItem(int pos) {
            return FRAGMENTS.get(pos);
        }

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

        @Override
        public CharSequence getPageTitle(int pos) {
            return TITLES[pos];
        }
    }
}

我创建的所有片段只覆盖了onCreateView()方法,因此我可以显示正确的XML布局.除此之外,他们是’股票’.为什么我不能与任何片段中的元素进行交互？

更新：

那么做这样的事情？

public class FragmentA extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle inState) {
        return inflater.inflate(R.layout.fragment_a,container,false);
    }

    public void setText(String text) {
        TextView t = (TextView) getView().findViewById(R.id.someTextView);  //UPDATE
        t.setText(text);
    }
}

分段的XML布局A.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/someTextView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:textSize="22sp" />

</LinearLayout>

public InstallAdapter(FragmentManager fm) {
            super(fm);
            FRAGMENTS = new ArrayList<Fragment>();
            FRAGMENTS.add(FragmentA.newInstance("<text to set to the TextView>"));
            FRAGMENTS.add(FragmentB.newInstance("<text to set to the TextView>"));
        }

//Declare your values for activity;
    ISetTextInFragment setText;
    ISetTextInFragment setText2;
...
//Add interface
public interface ISetTextInFragment{
    public abstract void showtext(String testToShow);
}
...
//your new InstallAdapter
public InstallAdapter(FragmentManager fm) {
        super(fm);

        FRAGMENTS = new ArrayList<Fragment>();

        Fragment fragA = new FragmentA();
        setText= (ISetTextInFragment)fragA;
        FRAGMENTS.add(fragA);

        Fragment fragB = new FragmentB();
        setText2= (ISetTextInFragment)fragB;
        FRAGMENTS.add(fragB);
}

//then,you can do this from your activity:
...
setText.showtext("text to show");
...

public class FragmentA extends Fragment implements ISetTextInFragment {

    TextView myTextView;

    @Override
    public View onCreateView(LayoutInflater inflater,Bundle inState) {
        View v = inflater.inflate(R.layout.fragment_a,false);
        myTextView = (TextView)v.findViewbyId(R.id.someTextView)
        return v;
    }

    @Override
    public void showtext(String text) {
        myTextView.setText(text);
    }
}