Question

我正在按照教程了解ViewPager的工作原理。当我运行应用程序时没有问题，但是当我滑动移动到Pager应用程序崩溃的第二页时，Logcat会生成以下错误。如果我错过了什么，请查看代码并告诉我。

ViewPager_Activity：

public class ViewPager00 extends FragmentActivity {

private MyAdapter mAdapter;
private ViewPager mPager;

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

    mAdapter = new MyAdapter(getSupportFragmentManager());

    mPager = (ViewPager) findViewById(R.id.pager);
    mPager.setAdapter(mAdapter);
}

public static class MyAdapter extends FragmentPagerAdapter {

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

    @Override
    public Fragment getItem(int position) {
        // TODO Auto-generated method stub
        switch (position) {

        case 0:
            return new DetailFragment();
        case 1:
            return new ImageFragment();
        default:
            return null;
        }
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return 3;
    }

}

}

Details_Fragment：

public class DetailFragment extends Fragment {


private static final String TAG = "DetailFragment";

@Override
public void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    Log.e(TAG, "@onCreate(): Hello");
}

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onActivityCreated(savedInstanceState);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    View view = inflater.inflate(R.layout.details,container, false);
    TextView textview = (TextView) view.findViewById(R.id.detailsText);
    textview.setText("Testing");
    return view;
}

}

Image_Fragment：

public class ImageFragment extends Fragment {


private static final String TAG = "ImageFragment";
//private final int imageResourceId;

//public ImageFragment() {}

/*public ImageFragment(int imageResourceId) {
    this.imageResourceId = imageResourceId;
}*/

@Override
public void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    Log.e(TAG, "@onCreate(): Hello");
}

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onActivityCreated(savedInstanceState);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    View view = inflater.inflate(R.layout.image,container, false);
    ImageView imageView = (ImageView) view.findViewById(R.id.imageView);
    //imageView.getResources().getDrawable(R.drawable.ic_launcher);

    return view;
}

}

logcat的：

06-23 12:45:32.995: E/AndroidRuntime(856): FATAL EXCEPTION: main
06-23 12:45:32.995: E/AndroidRuntime(856): Process: com.example.viewpager00, PID: 856
06-23 12:45:32.995: E/AndroidRuntime(856): java.lang.NullPointerException
06-23 12:45:32.995: E/AndroidRuntime(856):  at  
android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:394)
06-23 12:45:32.995: E/AndroidRuntime(856):  at 
android.support.v4.app.BackStackRecord.add(BackStackRecord.java:389)
06-23 12:45:32.995: E/AndroidRuntime(856):  at  


android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:99)
06-23 12:45:32.995: E/AndroidRuntime(856):  at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:832)
06-23 12:45:32.995: E/AndroidRuntime(856):  at android.support.v4.view.ViewPager.populate(ViewPager.java:1048)
06-23 12:45:32.995: E/AndroidRuntime(856):  at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
06-23 12:45:32.995: E/AndroidRuntime(856):  at android.support.v4.view.ViewPager$3.run(ViewPager.java:244)
06-23 12:45:32.995: E/AndroidRuntime(856):  at  android.view.Choreographer$CallbackRecord.run(Choreographer.java:803)

Answer 1

您的getCount()返回3，但getItem()仅为索引0和1返回非空值。将计数更改为2或使getItem()返回三项。

浏览ViewPager时的NPE

1 个答案: