Question

我在FragmentActivity中使用dispatchKeyEvent并调用我的一个片段方法。以下是我用于FragmentActivity的代码：

public class ViewPagerFragment extends FragmentActivity{
    MyAdapter mAdapter;
    ViewPager mPager;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.viewpager_layout);

        mAdapter = new MyAdapter(getSupportFragmentManager());
        mPager = (ViewPager) findViewById(R.id.pager);
        mPager.setAdapter(mAdapter);

        mPager.setCurrentItem(0);
    }

    public void onResume() {
        super.onResume();
    }

    public void onPause() {
        super.onPause();
    }

    public void onDestroy() {
        super.onDestroy();
    }

   @Override
    public boolean dispatchKeyEvent(KeyEvent event) {

        if(event.getKeyCode() == 66){
            FragmentPagerAdapter fragmentPagerAdapter = (FragmentPagerAdapter) mPager.getAdapter();
            ((SecondFragment)fragmentPagerAdapter.getItem(1)).myOnKeyDown(input_str);
        }

        return super.dispatchKeyEvent(event);
    }

    public void onNewIntent(Intent intent) {
        super.onNewIntent(getIntent());
    }

    public static class MyAdapter extends FragmentPagerAdapter {
        public MyAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public int getCount() {
            return 2;
        }

        @Override
        public Fragment getItem(int position) {
            switch (position) {
            case 0:
                return new FirstFragment();
            case 1:
                return new SecondFragment();

            default:
                return null;
            }
        }
    }
}

以下是我的SecondFragment的代码。

public class SecondFragment extends Fragment{
    ProgressBar spinner;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    public void onResume(){
        super.onResume();
    }    

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.secondfragment_layout, container, false);

        spinner = (ProgressBar) view.findViewById(R.id.spinner);

        return view;
    }

    public void myOnKeyDown(String barcode){
        // following line gives NullPointerException
        spinner.setVisibility(ProgressBar.VISIBLE);
    }
}

在我的SecondFragment的onCreateView中，我初始化了ProgressBar，它位于SecondFrament布局文件中。但是当我从FragmentActivity中的dispatchKeyEvent调用myOnKeyDown时，它总是变为null。为什么会如此，我该如何解决？提前谢谢。

Answer 1

你的SecondFragment的onCreateView（）方法需要返回视图。

 return view;

试试。

当我从FragmentActivity调用Fragment的方法时，为什么ProgressBar变为null？

1 个答案: