屏幕旋转后片段活动的引用问题

Question

我有一个带有两个“操作栏选项卡”的Activity，每个选项卡中都有一个片段。一切都正常工作，直到屏幕旋转。我在活动中有对片段的引用。如果我从我的Activity调用片段的方法，而该方法调用getActivity()，那么getActivity()会返回null。

我不知道是否应该将片段引用为Activity类的成员字段。如果我不能在activity类中保持该引用，如何获取片段布局中某些字段的值。

下面是我的活动类：

public class MyActivity extends ActionBarActivity implements ActionBar.TabListener {

    private ViewPager viewPager;
    private MyPagerAdapter pagerAdapter;
    private ActionBar actionBar;
    DetallesAvisoFragment fragment1;
    DetallesPiezaFragment fragment2;
    ActionMode actionMode;

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

        actionBar = getSupportActionBar();
        actionBar.setDisplayHomeAsUpEnabled(true);
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);


        viewPager = (ViewPager) findViewById(R.id.viewPager);
        Intent intent = getIntent();
        fragment1 = new Fragment1();
        fragment2 = new Fragment2();
        List<Fragment> fragmentList = new ArrayList<Fragment>();
        fragmentList.add(fragment1);
        fragmentList.add(fragment2);
        pagerAdapter = new MyPagerAdapter(getSupportFragmentManager(), fragmentList);
        viewPager.setAdapter(pagerAdapter);
        viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int i, float v, int i2) {

            }

            @Override
            public void onPageSelected(int i) {
                actionBar.setSelectedNavigationItem(i);
            }

            @Override
            public void onPageScrollStateChanged(int i) {

            }
        });
        actionBar.addTab(actionBar.newTab().setText("Frag1 Tab").setTabListener(this));
        actionBar.addTab(actionBar.newTab().setText("Frag2 Tab").setTabListener(this));
    }




    @Override
    public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
        viewPager.setCurrentItem(tab.getPosition());
    }

    @Override
    public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {

    }

    @Override
    public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {

    }

    /**
     * This method work properly until screen rotation
     */
    public void getValues() {
        String value1 = fragment1.getValueFromSomeField();
        String value2 = fragment2.getValueFromOtherField();
    }
}

FragmentPagerAdapter 类：

public class MyPagerAdapter extends FragmentPagerAdapter{

    List<Fragment> fragmentList;

    public MyPagerAdapter(FragmentManager fm, List<Fragment> fragments) {
        super(fm);
        fragmentList = fragments;
    }

    @Override
    public Fragment getItem(int index) {
        if (index >= fragmentList.size()) {
            return null;
        }
        return fragmentList.get(index);
    }

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

我的Fragment类：

public class Fragment1 extends Fragment {

    public Fragment1() {
    }



    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceBundle) {
        return inflater.inflate(R.layout.fragment1_layout, container, false);;
    }


    public String getValueFromSomeField() {
        TextView testView = (TextView) getActivity().findViewById(R.id.someField);
        return testView.getText().toString();
    }
}


public class Fragment2 extends Fragment {

    public Fragment2() {
    }



    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceBundle) {
        return inflater.inflate(R.layout.fragment2_layout, container, false);;
    }


    public String getValueFromSomeOtherField() {
        TextView testView = (TextView) getActivity().findViewById(R.id.someOtherField);
        return testView.getText().toString();
    }
}

注意：我需要支持SDK 8，因此必须使用SupportLibrary来使用Fragments。

- David SN

Answer 1

你需要声明。

static final String STORE_FRAGMENT1 = "fragment1";
static final String STORE_FRAGMENT2 = "fragment2";

你需要重写 onSaveInstanceState 方法来保存标签 fragment1 和 fragment2；

@Override
protected void onSaveInstanceState(Bundle savedInstanceState) {
    if (fragment1 != null) {
        savedInstanceState.putString(STORE_FRAGMENT1,
                fragment1.getTag());
    }
    if (fragment2 != null) {
        savedInstanceState.putString(STORE_FRAGMENT2,
                fragment2.getTag());
    }

    super.onSaveInstanceState(savedInstanceState);
}

当 OnCreated 时，您可以获取标签 fragment1 和 fragment2，以便在旋转之前保存 fragment1 和 fragment2。

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

        actionBar = getSupportActionBar();
        actionBar.setDisplayHomeAsUpEnabled(true);
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);


        viewPager = (ViewPager) findViewById(R.id.viewPager);
        Intent intent = getIntent();
        //----edit-------

        String TagFragment1;
        String TagFragment2;
        if (savedInstanceState != null) {
                    FragmentManager fm = getSupportFragmentManager();
            TagFragment1 = savedInstanceState.getString(STORE_FRAGMENT1);
            fragment1 = (SubjectFragment) fm
                    .findFragmentByTag(TagFragment1);
            TagFragment2 = savedInstanceState.getString(STORE_FRAGMENT2);
            fragment2 = (CircuitFragment) fm
                    .findFragmentByTag(TagFragment2);

        }
        else {
            fragment1 = new Fragment1();
            fragment2 = new Fragment2();
        }
        //---end--edit-----
        List<Fragment> fragmentList = new ArrayList<Fragment>();
        fragmentList.add(fragment1);
        fragmentList.add(fragment2);
        pagerAdapter = new MyPagerAdapter(getSupportFragmentManager(), fragmentList);
        viewPager.setAdapter(pagerAdapter);
        viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int i, float v, int i2) {

            }

            @Override
            public void onPageSelected(int i) {
                actionBar.setSelectedNavigationItem(i);
            }

            @Override
            public void onPageScrollStateChanged(int i) {

            }
        });
        actionBar.addTab(actionBar.newTab().setText("Frag1 Tab").setTabListener(this));
        actionBar.addTab(actionBar.newTab().setText("Frag2 Tab").setTabListener(this));
    }

- duc