Question

我有一个名为MainActivity的活动，里面有一个名为'HomeFragment'的片段。我希望在屏幕旋转后恢复片段，但似乎缺少某些东西。我按照以下流程：

在getSupportFragmentManager().putFragment(...)

onSaveInstanceState

尝试在onCreate期间通过fragmentManager.findFragmentByTag恢复片段（在检查该捆绑包不为空之后）

但是findFragmentByTag返回null。

以下是MainActivity中的代码段：

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Set up the action bar to show a dropdown list.
        final ActionBar actionBar = getSupportActionBar();
        actionBar.setDisplayShowTitleEnabled(false);
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_LIST);
        setupNavigationSpinner(actionBar);
        FragmentManager fragmentManager = getSupportFragmentManager();

        if (savedInstanceState != null) {

            if (fragmentManager.findFragmentByTag("frag") != null) { 
                //  findFragmentByTag always return null
                homeFragment = (HomeFragment) fragmentManager
                        .findFragmentByTag(HomeFragment.ARG_ITEM_ID);
                contentFragment = homeFragment;
            }else{
                homeFragment = new HomeFragment();
                switchContent(homeFragment, HomeFragment.ARG_ITEM_ID);
            }
        } else {
            homeFragment = new HomeFragment();
            switchContent(homeFragment, HomeFragment.ARG_ITEM_ID);
        }

}


@Override
public void onSaveInstanceState(Bundle outState) {
    getSupportFragmentManager().putFragment(outState, "frag",homeFragment );
}

public void switchContent(Fragment fragment, String tag) {
    FragmentManager fragmentManager = getSupportFragmentManager();
    while (fragmentManager.popBackStackImmediate())
        ;

    if (fragment != null) {
        FragmentTransaction transaction = fragmentManager
                .beginTransaction();
        transaction.replace(R.id.content_frame, fragment, tag);
        // Only ArticlDetailFragment is added to the back stack.
        if (!(fragment instanceof Fragment)) {
            transaction.addToBackStack(tag);
        }
        transaction.commit();
        contentFragment = fragment;
    }
}

Answer 1

没有理由打电话

getSupportFragmentManager().putFragment(outState, "frag",homeFragment );

将自动恢复Fragment状态。问题是你没有打电话给onSaveInstanceState的超级。它应该看起来像这样：

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

此外，您将代码设置为HomeFragment.ARG_ITEM_ID，然后查找"frag"。是HomeFragment.ARG_ITEM_ID == "frag"吗？

Android轮换：为什么片段没有被TAG恢复？

1 个答案: