我在Android中玩碎片。
我知道我可以通过使用以下代码更改一个片段:
FragmentManager fragMgr = getSupportFragmentManager();
FragmentTransaction fragTrans = fragMgr.beginTransaction();
MyFragment myFragment = new MyFragment(); //my custom fragment
fragTrans.replace(android.R.id.content, myFragment);
fragTrans.addToBackStack(null);
fragTrans.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
fragTrans.commit();
我的问题是，在Java文件中，如何获得当前显示的片段实例?
当前回答
如果你从父活动中获得Fragment的当前实例，你可以
findFragmentByID(R.id.container);
这实际上是视图中填充的fragment的当前实例。我也有同样的问题。我不得不加载相同的片段两次，保持一个备份。
下面的方法不起作用。它只是得到一个带有标签的片段。不要在这个方法上浪费时间。我相信它有它的用途，但获得同一片段的最新版本不是其中之一。
findFragmentByTag()
其他回答
In the main activity, the onAttachFragment(Fragment fragment) method is called when a new fragment is attached to the activity. In this method, you can get the instance of the current fragment. However, the onAttachFragment(Fragment fragment) method is not called when a fragment is popped off the back stack, ie, when the back button is pressed to get the top fragment on top of the stack. I am still looking for a callback method that is triggered in the main activity when a fragment becomes visible inside the activity.
简单的方法:
Fragment fr=getSupportFragmentManager().findFragmentById(R.id.fragment_container);
String fragmentName = fr.getClass().getSimpleName();
在滚动片段的情况下，当你使用ViewPager类的实例时，假设mVeiwPager，你可以调用mviewpage . getcurrentitem()来获取当前片段int数。
在MainLayout.xml
<?xml version="1.0" encoding="utf-8"?> <android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:fitsSystemWindows="true" android:orientation="vertical" tools:context="unidesign.photo360.MainActivity"> <android.support.design.widget.AppBarLayout android:id="@+id/appbar" android:layout_width="match_parent" android:layout_height="wrap_content" android:fitsSystemWindows="false" android:theme="@style/AppTheme.AppBarOverlay" app:expanded="false"> <android.support.v7.widget.Toolbar android:id="@+id/main_activity_toolbar" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_weight="1" app:popupTheme="@style/AppTheme.PopupOverlay" app:title="@string/app_name"> </android.support.v7.widget.Toolbar> </android.support.design.widget.AppBarLayout> <android.support.v4.view.ViewPager android:id="@+id/view_pager" android:layout_width="match_parent" android:layout_height="wrap_content"> </android.support.v4.view.ViewPager> </android.support.design.widget.CoordinatorLayout>
在MainActivity.kt
class MainActivity : AppCompatActivity() { lateinit var mViewPager: ViewPager lateinit var pageAdapter: PageAdapter // ... override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) pageAdapter = PageAdapter(supportFragmentManager) mViewPager = findViewById(R.id.view_pager) // ... } override fun onResume() { super.onResume() var currentFragment = pageAdapter.getItem(mViewPager.currentItem) // ... }
每次当你显示fragment时，你必须把它标签放入backstack:
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.setTransition(FragmentTransaction.TRANSIT_ENTER_MASK);
ft.add(R.id.primaryLayout, fragment, tag);
ft.addToBackStack(tag);
ft.commit();
然后当你需要获取当前片段时，你可以使用这个方法:
public BaseFragment getActiveFragment() {
if (getSupportFragmentManager().getBackStackEntryCount() == 0) {
return null;
}
String tag = getSupportFragmentManager().getBackStackEntryAt(getSupportFragmentManager().getBackStackEntryCount() - 1).getName();
return (BaseFragment) getSupportFragmentManager().findFragmentByTag(tag);
}
如果你正在使用AndroidX导航:
val currentFragment = findNavController(R.id.your_navhost)?.currentDestination
有关此导航组件的更多信息: https://developer.android.com/guide/navigation/navigation-getting-started
