我如何在NavHostFragment中检索当前片段？

Question

我试图在新的导航组件中找到一个方法,但我没有找到任何相关的方法.

我目前的目的地是:

mainHostFragment.findNavController().currentDestination

但我无法获得任何对显示片段的引用.

Answer 1

参考显示的片段（AndroidX）：

public Fragment getForegroundFragment(){
    Fragment navHostFragment = getSupportFragmentManager().findFragmentById(R.id.nav_host_fragment);
    return navHostFragment == null ? null : navHostFragment.getChildFragmentManager().getFragments().get(0);
}

这里nav_host_fragment是一个在的IDfragment在你的标签activity_main.xml与android:name="androidx.navigation.fragment.NavHostFragment"

Answer 2

导航不提供任何获取当前目的地的实现(即片段本身)的机制.

根据活动的创建事件回调,您应该与Fragment by进行通信

• 让Fragment在其onAttach方法中注册回调,将Activity转换为您提供的接口的实例
• 使用ViewModel您的活动和片段用于通信的共享.

Answer 3

你可以这样做:

  override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)

        val navHostFragment = supportFragmentManager.fragments.first() as? NavHostFragment
        if(navHostFragment != null) {
            val childFragments = navHostFragment.childFragmentManager.fragments
            childFragments.forEach { fragment ->
                fragment.onActivityResult(requestCode, resultCode, data)
            }
        }
    }

但是对于更高级的通信,在Fragment.onAttach()(Fragment -> Activity rather one direction communication)和SharedViewModel中注册了回调方法的监听器(bidirectional重要的是要有ViewModelProviders, and Lifecycle owner that is scoped to getActivity())

Answer 4

基于其他答案

Fragment navHostFragment = getSupportFragmentManager().getPrimaryNavigationFragment();
Fragment fragment = navHostFragment.getChildFragmentManager().getFragments().get(0);

((Your Fragment Class) fragment).(public method inside the fragment)

为我工作

Answer 5

使用 Michal 的回答，我编写了这个扩展函数用于测试：

@Suppress("UNCHECKED_CAST")
fun <F : Fragment> AppCompatActivity.getFragment(fragmentClass: Class<F>): F? {
    val navHostFragment = this.supportFragmentManager.fragments.first() as NavHostFragment

    navHostFragment.childFragmentManager.fragments.forEach {
        if (fragmentClass.isAssignableFrom(it.javaClass)) {
            return it as F
        }
    }

    return null
}

像这样使用：

val myFragment = activity.getFragment(MyFragment::class.java)

Answer 6

你可以这样做：

@Override
public void onBackPressed() {
    super.onBackPressed();
   
    NavController navController = Navigation.findNavController(this, R.id.fragment);
    int id=navController.getCurrentDestination().getId();
    if(id == R.id.startGameFragment ){
        selectedPosition(0);
    } else if(id == R.id.gameFragment ){
        selectedPosition(1);
    } else if(id == R.id.endGameFragment){
        selectedPosition(2);
    }
}

private void selectedPosition(int pos){
    for (int i = 0; i >=nav_view.getMenu().size(); i++) {
        nav_view.getMenu().getItem(pos).setChecked(false);

    }
    nav_view.getMenu().getItem(pos).setChecked(true);
}