Question

目前，我希望在配置更改期间保留昂贵的数据结构。我选择不使用Bundle来处理它，因为昂贵的数据结构是不可分割的。

因此，我使用非UI片段（称为 RetainInstanceFragment ），其setRetainInstance(true)来保存数据结构。

public class RetainInstanceFragment extends Fragment {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Creating expensive data structure
        expensiveDataStructure = CreateExpensiveDataStructure();

        // Tell the framework to try to keep this fragment around
        // during a configuration change.
        setRetainInstance(true);
    }

    public ExpensiveDataStructure expensiveDataStructure = null;
}

UI片段（称为 UIFragment ）将从RetainInstanceFragment获取昂贵的数据结构。每当UIFragment上的配置发生变化时，UIFragment将始终尝试从RetainInstanceFragment获取“缓存”FragmentManager，然后才决定创建新的RetainInstanceFragment 。

示例代码如下。

public class UIFragment extends SherlockListFragment
    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        FragmentManager fm = getFragmentManager();

        // Check to see if we have retained the worker fragment.
        retainInstanceFragment = (RetainInstanceFragment)fm.findFragmentByTag("data");

        // If not retained (or first time running), we need to create it.
        if (retainInstanceFragment == null) {
            retainInstanceFragment = new RetainInstanceFragment();
            fm.beginTransaction().add(watchlistArrayFragment, "data").commit();
        } else {
            // We can re-use retainInstanceFragment.expensiveDataStructure even
            // after configuration change.
        }
    }
}

但是，有一个问题。每当我销毁旧的UIFragment，并将其替换为新的UIFragment时，我希望旧的RetainInstanceFragment也会被销毁。以下是我如何销毁和创建新UIFragment

public class MyFragmentActivity extends SlidingFragmentActivity    
    // Being triggered when there is different menu item in sliding menu being
    // selected.
    public void selectActiveContent(Country country) {
        Fragment fragment = new UIFragment(country);
        getSupportFragmentManager().beginTransaction().replace(R.id.content, fragment).commitAllowingStateLoss();
    }

但旧的RetainInstanceFragment永远不会被销毁。

我的猜测是，也许我忘了在UIFragment进行清理。因此，我添加以下代码

UIFragment

@Override
public void onDetach() {
    super.onDetach();
    // To differentiate whether this is a configuration changes, or we are
    // removing away this fragment?
    if (this.isRemoving()) {
        FragmentManager fm = getFragmentManager();
        fm.beginTransaction().remove(retainInstanceFragment).commit();
    }
}

然而，它并不是一直有效。我执行了几次滑动菜单点击。

1. selectActiveContent() -> Create new UIFragment and new RetainInstanceFragment
2. selectActiveContent() -> Create new UIFragment, but re-use previous RetainInstanceFragment. (Wrong behavior)
3. selectActiveContent() -> Create new UIFragment, and new RetainInstanceFragment.
4. selectActiveContent() -> Create new UIFragment, but re-use previous RetainInstanceFragment. (Wrong behavior)

知道如何正确删除保留的实例片段吗？

Answer 1

正如@Luksprog所建议的，以下方法有效。 但是，它仍然无法解释为什么通过onDetach完成的上一次清理工作不起作用。如果有人能解释为什么这个解决方案有效，而以前没有，我会非常感激。：）

UIFragment

@Override
public void onDetach() {
    super.onDetach();
}

public void cleanupRetainInstanceFragment() {
    FragmentManager fm = getFragmentManager();
    fm.beginTransaction().remove(this.retainInstanceFragment).commit();
}

MyFragmentActivity

public class MyFragmentActivity extends SlidingFragmentActivity    
    // Being triggered when there is different menu item in sliding menu being
    // selected.
    public void selectActiveContent(Country country) {

        // *******************************************
        // Solution suggested by @Luksprog. It works!
        // But I have no idea why it works and previous doesn't work...
        // *******************************************
        Fragment oldFragment = getSupportFragmentManager().findFragmentById(R.id.content);
        if (oldFragment instanceof UIFragment) {
            ((UIFragment)oldFragment).cleanupRetainInstanceFragment();
        }

        Fragment fragment = new UIFragment(country);
        getSupportFragmentManager().beginTransaction().replace(R.id.content, fragment).commitAllowingStateLoss();
    }

（已编辑）@Luksprog的有用评论

片段交易不是马上进行的。我的假设是在onDetach（）回调中执行该事务不会删除在UI片段替换之前保留片段实例事务已完成，因此您的新UI片段仍会看到保留片段实例仍然可用，因此不会创建新的一。您以前的方法不符合片段的精神片段不知道其他片段和片段活动管理所有这些，因为它更了解整体申请状态。

Answer 2

我认为你可以从片段事务中删除片段。

            if (mWorkFragment != null) {
              fm.beginTransaction().remove(mWorkFragment).commitAllowingStateLoss();
            }

如何正确删除保留的实例片段

UIFragment

2 个答案:

UIFragment

MyFragmentActivity

（已编辑）@Luksprog的有用评论