java - 屏幕旋转后的 fragment Activity 引用

Question

我有一个 Activity，它有两个 Action bar tabs，每个选项卡中有一个 fragment 。一切正常，直到屏幕旋转。我引用了我 Activity 中的 fragment 。如果我从我的 Activity 中调用 fragmet 的方法并且该方法调用 getActivity()，则 getActivity() 返回 null。

我不知道我是否不应该将 fragment 引用作为我的 Activity 类的成员字段。如果我不能在 Activity 类中保留该引用，我如何才能在 fragment 的布局中获取某些字段的值。

这是我的 Activity 课:

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();
    }
}

还有我的 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:我需要对 SDK 8 的支持，所以我必须使用 SupportLibrary 来使用 fragment

Answer 1

你声明

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

您重写 onSaveInstanceState 方法以保存标签 fragment1 和 fragment 2；

@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 时你得到标签 fragment1 和 fragment 2 以在旋转之前保存 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));
    }