Question

对于我的应用程序，某些片段要求用户在显示之前在对话框中输入一个图钉。我有一个BaseFragment类，如果需要引脚，我所有其他片段都会扩展存储。我现在的问题是处理后退按钮，好像用户试图回到需要首先显示引脚对话框所需的引脚的片段。

目前我正在覆盖onBackPressed（），其中我想查看backstack以查看如果调用popBackstack（）将会恢复哪些片段，这样我就可以检查是否应该显示pin对话框。下面是我当前的代码，popFragment将返回null：

@Override
public void onBackPressed() {
    if(getSupportFragmentManager().findFragmentById(R.id.fragment_container) instanceof BaseFragment) {
        BaseFragment frag = (BaseFragment) getSupportFragmentManager().findFragmentById(R.id.fragment_container);

        if (getSupportFragmentManager().getBackStackEntryCount() > 0) {
            int index = getSupportFragmentManager().getBackStackEntryCount() - 1;
            Log.e("Back stack", Integer.toString(index));
            FragmentManager.BackStackEntry backEntry = (FragmentManager.BackStackEntry) getSupportFragmentManager().getBackStackEntryAt(index);

            BaseFragment popFragment = (BaseFragment) getSupportFragmentManager().findFragmentById(backEntry.getId());

            BaseFragment.checkAuth(this, frag, popFragment, new NavigationCallback((AppCompatActivity) this));
        } else {
            super.onBackPressed();
        }
    } else {
        super.onBackPressed();
    }
}

我已经检查过backEntry是否为null而不是。 backEntry.getId（）也返回值为1，因此我不确定为什么findFragmentById（）为null。我也不认为它与我如何显示片段有关，但这里也是我的代码：

FragmentManager fragManager = mActivity.getSupportFragmentManager();
FragmentTransaction transaction = fragManager.beginTransaction();
transaction.replace(R.id.fragment_container, mFragment);
transaction.addToBackStack(null);
transaction.commit();

Answer 1

BackStackEntry ID和Fragment ID与彼此无关。

我通过使用标签做了类似于你正在做的事情。同样，BackStackEntry代码和Fragment代码彼此无关;但是，通过对两个标签使用相同的值，您可以实现目标。

String tag = ...
FragmentManager fragManager = mActivity.getSupportFragmentManager();
FragmentTransaction transaction = fragManager.beginTransaction();
// tag is associated with fragment
transaction.replace(R.id.fragment_container, mFragment, tag);
// same tag is associated with back stack entry
transaction.addToBackStack(tag);
transaction.commit();

...

int count = fragmentManager.getBackStackEntryCount();
if (count > 0) {
    FragmentManager.BackStackEntry topBackStackEntry = 
            fragmentManager.getBackStackEntryAt(count - 1);
    String tag = topBackStackEntry.getName();

    if (tag != null) {
        Fragment fragment = fragmentManager.findFragmentByTag(tag);
        if (fragment != null) {
            // we found the fragment
            // you can also sanity-check here with fragment.isResumed()
        }
    }
}

Answer 2

您不见了Frag-A-> Frag-B-> Frag-C。现在，您想返回Frag-A而不为Frag-A创建新的Fragment视图吗？解决方法如下：

def split_into_batches(all_users, batch_size=BATCH_SIZE):
    """h/t: https://stackoverflow.com/questions/312443/how-do-you-split-a-list-into-evenly-sized-chunks"""
    for i in range(0, len(all_users), batch_size):
        yield all_users[i : i + batch_size]

def process_and_save_batch(user_rows, bq):
    print(generate_timestamp(), "|", current_thread().name, "|", "PROCESSING...")
    bq.append_user_friends([user_with_friends(user_row) for user_row in user_rows])
    print(generate_timestamp(), "|", current_thread().name, "|", "PROCESSED BATCH OF", len(user_rows))
    return True

service = BigQueryService() # a custom class defined elsewhere

users = service.fetch_remaining_users(min_id=MIN_ID, max_id=MAX_ID, limit=LIMIT)
print("FETCHED UNIVERSE OF", len(users), "USERS")

batches = list(split_into_batches(users))
print(f"ASSEMBLED {len(batches)} BATCHES OF {BATCH_SIZE}")

with ThreadPoolExecutor(max_workers=MAX_THREADS, thread_name_prefix="THREAD") as executor:

    for batch in batches:
        executor.submit(process_and_save_batch, batch, service)

还删除您的导航条目action_Frag_C_to_Frag_A。如果您不小心创建了导航图。

Android偷看后台堆栈没有弹出

2 个答案: