java - 在 Activity 中保存 fragment 状态

Question

当我尝试在主要 Activity 中保存 fragment 的状态时，出现以下错误:

java.lang.IllegalStateException: Fragment MarketviewFragment{c5e0f0d} is not currently in the FragmentManager
    at androidx.fragment.app.FragmentManagerImpl.putFragment(FragmentManager.java:923)
    at com.shoob.capstone.android.crypfolio.MainActivity.onSaveInstanceState(MainActivity.java:308)
    at android.app.Activity.performSaveInstanceState(Activity.java:1608)
    at android.app.Instrumentation.callActivityOnSaveInstanceState(Instrumentation.java:1443)
    at android.app.ActivityThread.callActivityOnSaveInstanceState(ActivityThread.java:5038)
    at android.app.ActivityThread.callActivityOnStop(ActivityThread.java:4372)
    at android.app.ActivityThread.handleRelaunchActivityInner(ActivityThread.java:4986)
    at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4922)
    at android.app.servertransaction.ActivityRelaunchItem.execute(ActivityRelaunchItem.java:69)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1926)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:214)
    at android.app.ActivityThread.main(ActivityThread.java:6986)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1445)

在我的主要 Activity 中，我有 4 个可能的 fragment ，一次仅显示一个。我在主要 Activity 中保留对 fragment 的引用并根据需要显示它们:

private MarketviewFragment marketviewFragment;
private WatchlistFragment watchlistFragment;
private PortfolioFragment portfolioFragment;
private DetailsFragment detailsFragment;

我使用以下代码设置当前显示的 fragment (一次仅显示一个 fragment ):

//fragment is an instance of one of the 4 types of fragments above
private void setFragment(Fragment fragment) {
    FragmentManager fm = getSupportFragmentManager();

    if (fm.findFragmentById(R.id.frag_main) != null) {
        fm.beginTransaction()
                .replace(R.id.frag_main, fragment)
                .commit();
    } else {
        fm.beginTransaction()
                .add(R.id.frag_main, fragment)
                .commit();
    }
}

这是我设置每个 fragment 的方式(一个示例，其他类型相同):

private void setPortfolioFragment() {
    if (portfolioFragment == null) {
        portfolioFragment = PortfolioFragment.newInstance();
    }
    setFragment(portfolioFragment);
}

现在回答我的问题。如何保存所有这些 fragment 的状态？我想将它们全部保存在一个 bundle 中，以便我可以在重新创建主要 Activity 时恢复它们(例如轮换)。

我现在的方法似乎不起作用，正确的方法是什么？

保存状态:

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);

    if (marketviewFragment != null) {
        getSupportFragmentManager().putFragment(outState, KEY_BUNDLE_MARKETVIEW_FRAGMENT, marketviewFragment);
    }
    if (watchlistFragment != null) {
        getSupportFragmentManager().putFragment(outState, KEY_BUNDLE_WATCHLIST_FRAGMENT, watchlistFragment);
    }
    if (portfolioFragment != null) {
        getSupportFragmentManager().putFragment(outState, KEY_BUNDLE_PORTFOLIO_FRAGMENT, portfolioFragment);
    }
    if (detailsFragment != null) {
        getSupportFragmentManager().putFragment(outState, KEY_BUNDLE_DETAILS_FRAGMENT, detailsFragment);
    }

}

恢复状态:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    if (savedInstanceState != null) {
        marketviewFragment = (MarketviewFragment)getSupportFragmentManager().getFragment(savedInstanceState, KEY_BUNDLE_MARKETVIEW_FRAGMENT);
        watchlistFragment = (WatchlistFragment)getSupportFragmentManager().getFragment(savedInstanceState, KEY_BUNDLE_WATCHLIST_FRAGMENT);
        portfolioFragment = (PortfolioFragment)getSupportFragmentManager().getFragment(savedInstanceState, KEY_BUNDLE_PORTFOLIO_FRAGMENT);
        detailsFragment = (DetailsFragment)getSupportFragmentManager().getFragment(savedInstanceState, KEY_BUNDLE_DETAILS_FRAGMENT);

    }
}

Answer 1

每次分离 fragment 时都应该保存它。 另外请在 fragmentManager

上使用 detach/attach 而不是 replace

另一件事是 FragmentManager 应该自行恢复 fragment 。就我个人而言，我会使用 FragmentPagerAdapter 来完成此操作，然后只切换可见的一个。

最好和最简单的方法是将所有 fragment 附加到 FragmentManager，并仅控制可见性。由于保存/恢复将自动完成