我已经不止一次地看到这个问题,但是我无法弄明白如何解决我的问题.
我有一个用户执行此操作的应用：
1 – 打开navigationDrawer并选择一个选项(创建一个片段)(我在这里选择第二个选项);
public void selectItem(int position) {
Fragment fragment = null;
switch (position) {
case FRAGMENT_OPTION1:
...
break;
case FRAGMENT_OPTION2:
fragment = ControlPanelFragment.newInstance();
break;
...
case FRAGMENT_OPTIONN:
...
return;
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.fragment_container,fragment).commitAllowingStateLoss();
}
}
2 – 加载所选选项(ControlPanelFragment)：
2.1 – 控制面板有标签和iconpager.对于每个寻呼机页面和每个选项卡,都会创建一个新的片段.我有3个标签和3个页面,因此创建了9个片段;
@Override
public void onViewCreated(View view,@Nullable Bundle savedInstanceState) {
super.onViewCreated(view,savedInstanceState);
if (savedInstanceState != null) {
currentControlPanelOption = savedInstanceState.getInt("currentControlPanelOption",currentControlPanelOption);
currentControlPanelTab = savedInstanceState.getInt("currentControlPanelTab",currentControlPanelTab);
}
setControlPanelTabs();
setIconPager();
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt("currentControlPanelOption",pager.getCurrentItem());
outState.putInt("currentControlPanelTab",mTabHost.getCurrentTab());
}
3 – 在setIconPager()中;我有这个代码：
pager = (ViewPager) view.findViewById(R.id.pager); cPanelPagerAdapter = new ControlPanelPagerAdapter(getChildFragmentManager()); pager.setOffscreenPageLimit(2); pager.setAdapter(cPanelPagerAdapter);
其中ControlPanelPagerAdapter具有以下代码：
public Fragment getItem(int index) {
Fragment fragment;
switch (index) {
case 1:
fragment = FragmentA.newInstance();
break;
case 2:
fragment = FragmentB.newInstance();
break;
case 3:
fragment = FragmentC.newInstance();
break;
default:
fragment = null;
break;
}
...
return fragment;
}
4 – FragmentA,FragmentB和FragmentC具有几乎相同的代码：
public static FragmentA newInstance() {
return new FragmentA();
}
@Override
public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_placeholder,container,false);
return view;
}
@Override
public void onViewCreated(View view,Bundle savedInstanceState) {
super.onViewCreated(view,savedInstanceState);
if (savedInstanceState == null) {
fragmentA_Data = new FragmentADetail[3];
createTabInstance(0);
} else {
fragmentA_Data = (FragmentADetail[]) savedInstanceState.getSerializable("Data");
return;
}
}
private void createTabInstance(int tab) {
new FragmentADetail();
fragment = FragmentADetail.newInstance(tab);
Bundle args = new Bundle();
args.putInt("tab",tab);
fragment.setArguments(args);
fragmentA_Data[tab] = fragment;
FragmentTransaction fragmentTransaction = getChildFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_placeholder,fragmentA_Data[tab]);
fragmentTransaction.commitAllowingStateLoss();
}
public void getTabData(int tab) {
if (fragmentA_Data[tab] == null) {
createStoreTimePeriodInstance(tab);
} else {
if (fragmentA_Data[tab].getArguments() == null) {
Bundle args = new Bundle();
args.putInt("tab",tab);
fragmentA_Data[tab].setArguments(args);
}
FragmentTransaction fragmentTransaction = getChildFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_placeholder,fragmentA_Data[tab]);
fragmentTransaction.commitAllowingStateLoss();
}
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putSerializable("data",fragmentA_Data);
}
5 – 最后,FragmentADetail有这个代码：
public static FragmentADetail newInstance(int tab) {
selectedTab = tab;
return new FragmentADetail();
}
@Override
public View onCreateView(LayoutInflater inflater,Bundle savedInstanceState) {
view = inflater.inflate(R.layout.details_fragment,false);
...
if (savedInstanceState != null) {
selectedTab = savedInstanceState.getInt("selectedTab");
}
...
}
public void getTabData(int tab) {
//This is where I'm getting the data that populates the layout
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt("selectedTab",selectedTab);
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
Bundle args = getArguments();
if (args != null) {
getTabData(args.getInt("tab"));
}
}
现在,想象一下我在FragmentA上选择了第三个标签.如果我旋转屏幕,我会有以下事件序列：
> ControlPanelFragment onSaveInstanceState保存当前选项卡和当前片段
> FragmentA onSaveInstanceState保存寻呼机的选项卡片段
> navigationDrawer第二个选项再次被称为fragment = ControlPanelFragment.newInstance();
>调用onConCreated的ControlPanelFragment,我可以获取保存的数据信息,并创建新的寻呼机和标签
>调用FragmentA onViewCreated,我可以提取保存的数据
> FragmentADetail onActivityCreated获取保存的数据并正确加载数据(至少我认为)
从现在起第二次调用第二组方法,之前保存的数据被重置,因此它现在显示错误的数据
> ControlPanelFragment onSaveInstanceState但现在savedInstanceState为null
> ControlPanelPagerAdapter getItem被调用实例化3个片段
> FragmentA onSaveInstanceState现在调用它,但savedInstanceState为null
>调用FragmentADetail onActivityCreated但现在tab = 0
有人可以解释一下 – 我怎么能阻止步骤7到10发生？
解决方法
我弄清楚我的问题是什么.
当我这样做时：
case FRAGMENT_OPTION2:
fragment = ControlPanelFragment.newInstance();
break;
我正在创建一个片段,当我旋转屏幕时,再次调用selectItem(int position),因此创建了相同对象的新实例,因此执行了步骤7及其后续步骤.解决方案是检查片段是否已经创建并使用他而不是创建新片段.
我用标签保存了初始片段,然后他们查找了那个标签.如果标签存在,请使用该片段,否则创建一个新片段.
public void selectItem(int position) {
Fragment fragment = null;
switch (position) {
case FRAGMENT_OPTION1:
...
break;
case FRAGMENT_OPTION2:
fragment = getSupportFragmentManager().findFragmentByTag(String.valueOf(position));
if (fragment == null) {
fragment = ControlPanelFragment.newInstance();
}
break;
...
case FRAGMENT_OPTIONN:
...
return;
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.fragment_container,fragment,String.valueOf(position)).commitAllowingStateLoss();
}
}
