我在使用 FragmentNotification 接口向 ViewPager 中的片段触发命令的 Activity 时遇到问题。一切正常，直到应用程序长时间处于后台或方向发生变化。此时，Activity 似乎与 Fragment 失去了联系。
我的活动代码：
public class MyActivity extends FragmentActivity implements MyFragment3.FragmentNotification {
SectionsPagerAdapter mSectionsPagerAdapter;
ViewPager mViewPager;
MyFragment1 fragOne = new MyFragment1();
MyFragment2 fragTwo = new MyFragment2();
MyFragment3 fragThree = new MyFragment3();
boolean toggle = false;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
...
setContentView(R.layout.activity_main);
// Create the adapter that will return a fragment for each of the three primary sections
// of the app.
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setOffscreenPageLimit(2);
mViewPager.setAdapter(mSectionsPagerAdapter);
mViewPager.setClickable(true);
mViewPager.setCurrentItem(0);
}
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if ((keyCode == KeyEvent.KEYCODE_BACK)) {
if (fragThree != null) {
fragThree.doSomething();
toggle = false;
return false;
} else {
}
}
return super.onKeyDown(keyCode, event);
}
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int i) {
Fragment fragment;
if(i==0){
fragment = fragOne;
}else if(i==1){
fragment = fragTwo;
}else{
fragment = fragThree;
}
return fragment;
}
@Override
public int getCount() {
return 3;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0: return getString(R.string.title_section1).toUpperCase();
case 1: return getString(R.string.title_section2).toUpperCase();
case 2: return getString(R.string.title_section3).toUpperCase();
}
return null;
}
}
//Receive an event notification from a fragment
// @Override
public void fragmentAction(int actionType) {
if (actionType == MyFragment3.TOGGLE_ACT) {
toggle = true;
}
}
}
我的片段代码：
public class MyFragment3 extends Fragment {
View mView;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
...
mView = ....
return rootView;
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
mListener = (FragmentNotification) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString() + " must implement OnArticleSelectedListener");
}
}
public void doSomething(){
mView.setVisibility(View.GONE);
...
}
public interface FragmentNotification {
public void fragmentAction(int actionType);
}
}
如前所述，在某些状态发生变化之前一切正常，然后看起来活动失去了对 viewpager 中存在的片段的引用，即使在按下后退按钮之前它正在正确显示。
我相信我需要通过从我的 Fragment 的 onSaveInstanceState 提供一个包来恢复连接，但不知道如何开始。
任何帮助将不胜感激。
谢谢，乔什