android - 使用 android 导航组件获取 Backstack 状态

Question

我想实现 backpress 行为，这样当你在 backstack 为空的情况下按下时它会提示确认弹出窗口，否则它会弹出堆栈中的下一个 fragment 。

我正在尝试获取 backstack 计数，但我总是从两个 fragment 管理器中得到 0

 getSupportFragmentManager().getBackStackEntryCount();
 getFragmentManager().getBackStackEntryCount();

我想它应该可以工作，因为我检查了 fragment 导航器的谷歌代码，它通过规范的 fragment 事务添加到后台:

fragment 导航器.java:

 if (initialNavigation || isClearTask) {
        backStackEffect = BACK_STACK_DESTINATION_ADDED;
    } else if (isSingleTopReplacement) {
        // Single Top means we only want one instance on the back stack
        if (mBackStack.size() > 1) {
            // If the Fragment to be replaced is on the FragmentManager's
            // back stack, a simple replace() isn't enough so we
            // remove it from the back stack and put our replacement
            // on the back stack in its place
            mFragmentManager.popBackStack();
            ft.addToBackStack(Integer.toString(destId));
            mIsPendingBackStackOperation = true;
        }
        backStackEffect = BACK_STACK_UNCHANGED;
    } else {
        ft.addToBackStack(Integer.toString(destId));
        mIsPendingBackStackOperation = true;
        backStackEffect = BACK_STACK_DESTINATION_ADDED;
    }
    ft.setReorderingAllowed(true);
    ft.commit();

我也没有找到任何 API 来通过 NavController 或 Navigator 检索此信息。

谢谢

Answer 1

也可能对某人有帮助:

<fragment
    android:id="@+id/YOUR_NAVIGATION_HOST_ID"
    android:name="androidx.navigation.fragment.NavHostFragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:defaultNavHost="true"
    app:navGraph="@navigation/YOUR_NAVIGATION_HOST" />

val navHostFragment = supportFragmentManager.findFragmentById(R.id.YOUR_NAVIGATION_HOST_ID)
val backStackEntryCount = navHostFragment?.childFragmentManager?.backStackEntryCount